The Manosphere Report

0:00The larger the number of older brothers that a male has, the higher the probability

0:05that he is gay. It's been seen over and over.

0:09I mean, it's really one of the rock -solid findings in human sexuality.

0:14So the way to emphasize the difference is if a baby boy is born today,

0:20if he has no older brothers, his odds of being gay when he grows up

0:25is about 2%, pretty low.

0:28But if he had one older brother, his odds go up by a third.

0:33Okay, 2 .6. And if he has two older brothers, they go up a third

0:36again. All right, now we're at 3 .5.

0:38It turns out you've got to have like a dozen older brothers just to have

0:41a 50 -50 chance. Welcome to the Huberman Lab podcast, where we discuss science and

0:46science -based tools for everyday life.

0:52I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of

0:57Medicine. My guest today is Dr.

0:59Mark Breedlove. Dr. Mark Breedlove is a professor of neuroscience at Michigan State University, and

1:05he is an expert in how hormones shape the developing brain, in particular, how they

1:10influence sexual orientation. As you'll learn today, the amount of testosterone that a fetus is

1:15exposed to while in the mother has a profound impact not only on the ratio

1:20of finger lengths, yes, you heard that right, but it also plays a meaningful role

1:24in sexual orientation. And in fact, there's a correlation there between finger length ratios and

1:30sexual orientation. Now, as wild as that may seem, that result has now been confirmed

1:35many times over in humans and in animals.

1:38And today, you'll understand why.

1:40You'll also learn that every time a woman is pregnant with a male, there's a

1:44biological trace of that, which biases the likelihood that her next male offspring will be

1:49either heterosexual or homosexual. Now, I know this sounds really out there, but these are

1:53extremely solid biological findings for which the mechanisms are now understood for both animals and

1:59humans. It turns out that the hormones we are exposed to while we are in

2:03the womb shape not only the preference for whether somebody is attracted to males or

2:07females, but also an aversion to the opposite, meaning there appears to be the formation

2:11of circuits for being attracted to one sex and not attracted to the other.

2:16Today, you'll also learn how hormones impact the amount of rough and tumble or social

2:20play that kids engage in, the interplay between nature and nurture in shaping male versus

2:24female differences, and sexual orientation.

2:27Dr. Breedlove is one of the longstanding pioneers in this field of how hormones shape

2:32brain development and psychology. We approach these questions through the lens of biology and statistics.

2:38So today's is not a political discussion.

2:41Instead, it's a discussion about what is known and what is still not known about

2:45this profound aspect of our species.

2:47Oh, and we also talk about gay rams.

2:50Yes, that's a real thing, and it has important implications for everything we've mentioned thus

2:54far. By the end of today's episode, you'll surely think differently about the relationship between

2:59hormones and brain development, nature and nurture, and romantic partner choice.

3:04Before we begin, I'd like to emphasize that this podcast is separate from my teaching

3:08and research roles at Stanford.

3:10It is, however, part of my desire and effort to bring zero cost to consumer

3:13information about science and science -related tools to the general public.

3:17In keeping with that theme, today's episode does include sponsors.

3:21And now for my discussion with Dr.

3:23Mark Breedlove. Dr. Mark Breedlove, welcome.

3:26Thank you. I'm delighted to be here.

3:28Very exciting. Been 25 years since we stood in the same physical space.

3:32I know. How can that be possible when I feel like, you know, just saw

3:37you a few days ago, but then...

3:38Well, you look great. Thank you.

3:40You look the same, so we can talk longevity protocols at the end, but...

3:43I'm trying to have a blonde look in my hair, apparently, so...

3:45Well, I've wanted to have you on this podcast since I launched it because you

3:50work on one of the most interesting things in the world, which is how and

3:55why people become who they are and how hormones play a role there, how genes

4:00play a role there. If you're willing, I'd like to jump from the high dive

4:04to the deep end first, right off.

4:06All right. Let's talk about this finger length ratios, sexual orientation study that you published

4:13and somehow I landed on that paper.

4:15That's not why I want to talk about it.

4:17I want to talk about it because it's an incredibly interesting set of findings.

4:20Other people have done the same -ish experiments, and there's a whole context there about

4:26how hormones influence sexual orientation independent of behavior.

4:31We need to step back a little bit for the context.

4:34One thing that your listeners might not know is, you know, in the year 2000,

4:38there was still a lot of people who regarded same -sex orientation as a choice,

4:45a lifestyle choice. That was the political combination of words that meant you could disapprove

4:52of people because they were attracted to the same sex.

4:55Of course, I'm at Berkeley.

4:57I didn't have any truck with such notions at all, and I've always been convinced

5:02that sexual orientation is not a choice, and there's an exercise they do in class

5:07where I ask, so I'm going to put you to it.

5:09So remember the first time you had a crush, right?

5:13It might have been someone on TV.

5:14It might have been someone on a playground, et cetera.

5:16So think about it, and I want you to tell me about how old you

5:19were at the time in a moment.

5:21My guess is it was before puberty.

5:23Yeah, I was sick. And I hit puberty somewhere starting around 14.

5:28So it had nothing to do with puberty, right?

5:31It was this thing that happened.

5:33And I'll share my experience.

5:35So I'm about six or seven.

5:36I couldn't have been more than seven.

5:38And Marilyn Monroe is on TV.

5:40I'm dating myself. And there's a close -up, you know, with that face and the

5:45mole, et cetera. And afterwards, I'm just so agitated.

5:50I don't, you know, I don't – and I know nothing about sex.

5:53I remember I had a hard time going to sleep.

5:55So it was like something about this was really agitating me.

5:59And I didn't choose to have that reaction.

6:03And my guess is that whatever sex you had your first crush on, that's the

6:07one you're going to be attracted to the rest of your life.

6:10Yeah, it's been constant. Yeah.

6:12So this idea that it was a choice, that always just seems so absurd to

6:16me. On the other hand, even though, you know, I've been doing animal research with

6:23giving hormones early in life and seeing what it did to the nervous system, et

6:26cetera, and every time I wrote an NIH grant, I said, well, you know, the

6:31effect of early hormones may be important for human behavior.

6:33But to tell you the truth, I never actually believed that, right?

6:37It was just – I just wanted to justify it because it seemed to me

6:41that we are so sensitive to social influences.

6:45And we have this long stretch of time where we're – you know, our brains

6:51are still growing at a fetal rate of growth until like nine or ten years

6:55of age. And we're taking in so much information.

6:57And think of what a heterosexual world it is, right?

7:01I've got all those Disney movies with Prince Charming and et cetera.

7:05And so it always seemed to me that social learning would be more than enough

7:12to explain why 95 percent of people are straight.

7:15But that doesn't mean that was a choice and it doesn't mean that they would

7:18even be aware of what the social influence was.

7:21So my example is I speak English.

7:24It's – you know, I'm hopelessly monolingual, only language I speak.

7:26Well, I don't remember learning English and I certainly didn't choose to learn English, but

7:32I'm sure that it's English because of social influences, right?

7:36So that was where I stood on the question of sexual orientation until 1998, 1999

7:43when this fellow at University of Texas, Dennis McFadden, came out with a paper where

7:51it really made me think that prenatal testosterone might have an effect after all, despite

7:58my expectations. And this was looking at otoacoustic emissions.

8:03Do you want to talk about those?

8:04These are people's ears making noise.

8:07Yeah. I mean right now in this studio, if I shut up for a moment,

8:12your ears will continue to make little popping sounds that you're not aware of because

8:17having grown up with it, the brain stops you from perceiving those long ago.

8:22Well, but if Dennis puts you in a soundproof room and puts a very sensitive

8:26microphone in your ear, he'll hear these pops.

8:30And I won't get into the acoustics of why that's a good thing, right?

8:34It helps you to focus on the sounds you want to hear.

8:38But what Dennis knew is there's a sex difference in how many of these otoacoustic

8:45emissions are being made. Girls make more, and it's present at birth.

8:50So Dennis comes out with a strange study.

8:53I mean, who would do such a thing where he proposes, well, since the sex

8:57difference is present at birth, it might reflect prenatal testosterone.

9:01And so he measured the otoacoustic emissions in straight men and gay men and straight

9:07women and lesbians. And he reports that compared to straight women, the lesbians have fewer

9:15of these otoacoustic emissions than straight women.

9:19It's like, well, what? How would that happen?

9:25I couldn't think of any way to explain that except that, well, the lesbians might

9:31have been exposed to more prenatal testosterone than straight women before birth.

9:36And I don't know how to explain that except to say, well, maybe prenatal testosterone,

9:40maybe if you're exposed to that before birth, you're more likely to be attracted to

9:43women when you grow up.

9:44Which, oh, well, that might explain why 95 % of men are attracted to women,

9:50right? Because they're all exposed to prenatal testosterone.

9:52So this oddball study really gets me to thinking that maybe there's, you know, something

9:57to that. But I'll forget it.

9:59You know, I'm still working with my rats and paromyscus and Siberian hamsters and stuff.

10:04I'm happily doing that. And then, and I remember it so well, in 1999, I'm

10:11in my office at Berkeley and I read this paper.

10:13It says there's a sex difference in the ratio of fingers that's present in nine

10:22-year -old children. What? I've studied sex differences my whole adult life.

10:27How do I not know about this?

10:28And it turns out that if you measure the length of the second digit, the

10:34pointer finger. The pointer finger.

10:36For those just listening, yeah.

10:37Right. And the length of the ring finger.

10:39And you can do a simple ratio.

10:41Divide the length of the second digit by the fourth digit, so -called 2D -4D

10:45ratio. And a guy named John Manning was reporting that there's a sex difference there.

10:52that it's, that that ratio tends to be smaller in men than in women and

10:57that it's present in children.

10:58It's like, well, wait a minute, a sex difference in the body that's present before

11:03puberty, I know enough about sexual differentiation in the body.

11:07It's almost certainly due to prenatal testosterone.

11:11Forgive me for interrupting you, but people are probably looking at their hands right now.

11:14And I just want to point out that these are averages, but it's, I think

11:19the 2D, 4D thing for people that aren't familiar, even though you explained it quite

11:22clearly, can be a little confusing.

11:23Basically in men, the finger lengths are more different than they are in women.

11:28And there are some differences in that statement, according to sexual orientation that we'll get

11:34into. But when you say the, in other words, the typical heterosexual male pattern is

11:41that the pointer finger, right, is shorter than the ring finger.

11:46Whereas in women, they tend to be more similar.

11:49Again, these are averages and not to give it away, but this is because people

11:54are looking at their fingers right now.

11:56Let me just say, don't panic.

11:59We're going to walk you through this.

12:01You're going to be fine.

12:01And the difference between men and women is more pronounced on the right hand, as

12:06I recall. That's true too.

12:08Did I earn my authorship on the paper?

12:10Well, that and the fact that you persuaded so many people to answer our weird

12:14questions and let us see rocks their hands.

12:16Okay. So please continue. But I know that the moment that came out, hopefully there

12:19were no car accidents that people were driving.

12:21But these are averages, but that's the pattern that was observed.

12:26That's the pattern. Well, I'd never worked with humans before, but I'm sitting in the

12:30Bay Area. We have loads of gay people around.

12:34So it's like, well, let's, I guess we could try to do this.

12:40And so we started going out to street fairs.

12:43You were, you were with us, uh, going out to street fairs and giving people,

12:48asking people questions, uh, asking them to fill out a questionnaire anonymously.

12:52And, um, and I remember it, it was one of the organizers of one of

12:57the street fair, but I said, well, what should we do as an incentive to

13:00get people in? And they said, well, offer them scratcher tickets.

13:04Lottery tickets. Lottery tickets. So, so we, we asked people, will you please answer these

13:08very personal questions about, about who you have sex with, who you want to have

13:12sex with, et cetera, and tell us everything about yourself anonymously.

13:17And we'll give you a $1 lottery scratcher people ticket.

13:20And people will do anything for a $1 lottery scratcher ticket.

13:25I mean, it was just a bit, which is weird because you do the math

13:28and the word, the word's like 27 cents, right?

13:30But, but, but people want them.

13:32Um, and oh, and by the way, can we Xerox your hands?

13:36And the last two questions we asked about handedness, just, but it was really just

13:39to, to keep them from panicking.

13:42Um, so, you know, uh, and it, by the way, it was, it was the

13:47least expensive experiment I'd ever done in my life because really, you know, compared to,

13:52to any experiment with rat where step one, buy a rat for 20 bucks, right?

13:57So it's, um, so, uh, and it was an odd experience going in the 7

14:02-Eleven that morning and saying, please, I'd like $750, $1 lottery scratcher tickets.

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16:49there are a lot of gay people in the Bay Area.

16:52But it was very clear, as I recall when doing this study, that if we

16:56wanted to get a large sample population of gay men, we would need to go

17:02to the Castro District in San Francisco.

17:04And if we needed to get a large cohort of gay women, we need to

17:07go to the Solano Street Fair in Berkeley.

17:10And in Oakland. So there was a brand new Oakland gay festival that got started.

17:16And yeah, Oakland is a wonderful place to find lesbians.

17:21So what are the charms of the place?

17:23I thought the whole idea was kind of crazy, actually.

17:26I mean, I didn't think we'd come up with anything.

17:28And I insisted on measuring all the digits myself, right?

17:32Which I did twice. Boring as hell.

17:35I recall when we were on what was like third floor of Tolman Hall and

17:39you came running in. I was talking to my advisor, our good friend Irv Zucker,

17:44one of the pioneers of circadian biology, discovered the suprachiasmatic nucleus with Bob Moore and

17:49others. And you came running in with a ruler and you said, give me your

17:55hands. And you grabbed my hands and you measured them and you go, well, that's

17:59weird because it's like different on one hand than the other.

18:02And then you go, okay.

18:03And you took the notes and he measured his hands and he left.

18:05And I thought, what in the world is he doing?

18:07It turns out that was the early origins of the study.

18:10Yeah. No, no. Anyway, so I measure these hands and I'm doing the math at

18:18the end of the day.

18:19And lo and behold, I mean, I don't see any difference in the digit ratios

18:23of gay and straight men, right?

18:25Okay. Between gay and straight men.

18:27Yeah. Yeah. I didn't see any difference there.

18:28Which itself is interesting. Absolutely.

18:30Because it implies more or less equivalent amounts of prenatal testosterone exposure.

18:35Which I think is the case.

18:36Yes. And right now, just forgive me, but some people might say, well, that's not

18:42surprising. But in the 80s and 90s, the Hollywood stereotype of gay men was that

18:47they were all very effeminate.

18:50Yep. Since then, there's been an evolution.

18:53In fact, I haven't seen it, but many people I know are very excited about

18:56this recent show about these two gay hockey players where, so the whole context is

19:00these guys that are very masculine, but are gay, right?

19:03So for people hearing this that are younger than 40, they're going to think, well,

19:08duh. But for people that grew up in my generation or your generation, it was

19:13a bit of a shocker to a lot of people because depending on their level

19:19of exposure to the gay community, they may or may not have realized that not

19:22all gay men are effeminate.

19:24Exactly. And you know, that idea that gay men might have been under androgenized, there

19:30was always a part of it that always seemed strange to me.

19:33So the big sex differences in human behavior are not in, you know, math skills

19:38and the verbal skills. Those are tiny, right?

19:40The really big sex differences in human behavior are in sexual attitudes.

19:45And the biggest sex difference is one sex is much more interested in multiple partners

19:52and younger partners than the other, right?

19:54Everyone knows which sex that is.

19:56One sex is much more interested in casual sex than the other.

20:00Everyone knows that. One sex is much more interested in visual pornography than the other

20:05sex. Those are huge sex differences compared to any, you know, cognitive things.

20:10And in all those ways, gay men are totally masculine.

20:15So how would that work that, you know, they were under androgenized and yet they

20:20have all these sex differences in sexual attitude.

20:23I think the difference between gay and straight men isn't in how much prenatal testosterone

20:27they got. I think it's in how their brains responded to the testosterone that they

20:33got. And we can talk about that some more later.

20:37But back to the digit ratios, the lesbians had more masculine digit ratios than the

20:41straight women on average. And as you say, that's been replicated by many different labs.

20:48Dave puts it at Penn State and Ashlyn Swift -Galant and I recently published like

20:56the third meta -analysis. And it's clear so many people have seen it.

21:00It's there. And as with Dennis's otoacoustic emissions, I don't know how to explain that.

21:06Why why would lesbians have a more masculine digit ratio than straight women unless on

21:13average they were exposed to more prenatal testosterone than straight women?

21:17And why would that matter unless being exposed to prenatal testosterone makes you more inclined

21:24to be attracted to women when you grow up?

21:26And what's really weird about it, think about the time lag.

21:29Your first crush, this sudden, this mysterious, for me, at least it was like a

21:35visitation, right? It's like, where'd this come from?

21:39That happened six years after you were out of the womb, right?

21:44And so it's really strange to think that something that happened to your book.

21:47before you were born would have an influence on who you're going to be attracted

21:52to six, ten years later when you have your first crush.

21:57So it was, and I can tell you that when we published that in 2000,

22:02it did cause quite an uproar.

22:06I heard from a lot of strangers that I'd never heard from before, and it

22:11was pretty interesting. Of course, there were several people wrote who had told me that

22:19they were gay, and they were very positive, very supportive.

22:22But I got lots of emails from people saying, I know you're lying.

22:26You're making this up to justify your gay lifestyle.

22:30It's like, well, okay, except I don't happen to be gay.

22:34I mean, we had a nice mix of orientations on the research team, but people

22:38were having a hard time with it.

22:41And to assure your listeners about, if they're looking at their hands, if they're a

22:46woman and they're looking at their hands and they see that the index finger is

22:50quite a bit shorter than the ring finger, and they're thinking, I thought I was

22:53straight, et cetera. So here's a joke that I tell, which is, if you want,

22:58I'm going to teach you right now.

23:00You gather a big sample of people, and I'm going to teach you how to

23:04look at their hands, look at the right hand, and guess their sexual orientation, and

23:07you're going to be right 95 % of the time.

23:11So look at the right hand, pay really careful attention to whether the index finger

23:16is shorter than the ring finger, and no matter what, you see, guess straight, and

23:22you will be right 95 % of the time if it was a random sample

23:25of people. So the important thing to get across is that while these average differences

23:32across group are theoretically important, because they do indeed indicate that lesbians are more likely

23:40to have been exposed to slightly more testosterone before birth, that doesn't mean you can

23:44predict how much testosterone one person was exposed to from their digital ratio, because other

23:50things influence the digital ratios.

23:52Fascinating study. I got made fun of quite a lot, but, you know, I thought

23:56it was a blast. I mean, some of the more outrageous things that people have

24:00asked me about the study over the years were, and by the way, they all

24:04came from men, were, if I cut off my index finger, you know, will that

24:11raise my testosterone? Someone actually asked that.

24:14Yep. No, it's not reverse causality.

24:16I would have said, well, let's try it and see.

24:19Again, now, most people, I realize there are differences across the country and the world

24:23on this stance, but I think most people would say, yeah, like, okay, there's a

24:28biological variable associated with sexual orientation.

24:32The fact that it's linked to prenatal testosterone is very interesting.

24:37And the question that then comes up is, is there anything about behaviors associated with

24:44gay or straight men, gay or straight women that change hormone levels independent of all

24:51this, right? Because put differently, I think for a number of years, people were interested

24:55in whether or not gay men, as you pointed out, would have higher or lower

24:59levels of testosterone. The hypothesis was lower based on the effeminate stereotype.

25:04Turned out probably the opposite outcome.

25:07If anything, you're right. Yeah.

25:08Right. Anyone that went to gyms in the 1980s and 90s would also realize that

25:15the low androgen argument was wrong, although steroids become a problem in gyms too, but,

25:21you know, it gets confounded.

25:22But am I correct in remembering that this effect is also present in frogs or

25:29mice? The sex difference is present in mice.

25:31That's D2 -D4 ratio difference.

25:32Yes. I find that amazing.

25:34Well, I did too. So, so, so, so, uh, Wendy Brown and I did that

25:40first and, you know, I'd worked with mice and rats all my life, but, you

25:44know, I'd never noticed that, that, that, that they're, this is their, that the first

25:48digit is the shortest and that the third digit is the longest and that sometimes

25:54the second digit is longer than, you know, it's like, I mean, it's, you know,

25:58evolution's real, right? It happened.

26:00Uh, and so, yeah, there's a sex difference there and a group looked at mice

26:04and did lots of genetic manipulations.

26:06And it turns out that if you, if you make the androgen receptor dysfunctional, the

26:12sex difference goes away. And they showed that in mice, at least there's more androgen

26:18receptor in the, the growing bones of the fourth digit than the second digit.

26:22And then they showed that, um, that that's why the fourth digit grows a little

26:27bit more than the second digit.

26:28Beautiful. So the, and we, I should have said this earlier, androgens are things like

26:32testosterone, um, DHT, other, other androgens, um, men and women both have them, uh, other

26:38animals have them. Um, incredible.

26:40So let's talk about effects of testosterone when we're in the womb.

26:47Yeah. Obviously it's having an organizing effect on the body plan, this D4, D2 ratio.

26:53Right. What about in the brain?

26:55What is known about brain differences between men and women that identify as straight or,

27:02um, gay? Well, in, in terms of prenatally, we don't know, but, but the very

27:08famous study from Simon LeVay, who was already a highly respected neuroscientist, lots of.

27:15wonderful papers and development of the visual system.

27:18Simon LeVay got everyone's attention well before we did when he looked at a brain

27:24region in the hypothalamus, a specific region called the pre -optic area or POA, and

27:30he looked there and compared the size of the POA in the brains of gay

27:36men versus straight men. And he looked in the pre -optic area because in rats

27:40there's a very prominent sexual difference or sex dimorphism in a nucleus in the rat

27:46brain in the pre -optic area, and the nucleus got named the sexually dimorphic nucleus

27:52of the pre -optic area, the SDNPOA.

27:56And Simon knew there was a huge sex difference there in rats, and so he

28:01looked at the brains of gay and straight men and found a nucleus there that

28:06may or may not be the same as the SDNPOA but is larger in men

28:09than in women. And what he found was that the nucleus in gay men was

28:15smaller than in straight men, and in fact not significantly different from the size of

28:20the nucleus in women. So it wasn't hyper -male like the finger length ratio was?

28:25No, no. In that case it indicated less either less androgen exposure or less of

28:33a response to the androgen that was there.

28:35And Simon got even more of an uproar than I did, published his paper in

28:41Science, and there were lots of people that were very skeptical, including some neuroscientists, but

28:47eventually another group replicated it.

28:50That's what I was going to ask because I recall that the two major critiques

28:53of the paper, one was fair in my opinion.

28:57It was that some of the post -mortem samples were from people who had died

29:00of AIDS, and so AIDS has some known neurodegenerative effects that may or may not

29:05have impacted the samples, although hopefully they control for that.

29:08And then as I recall, he also got some pushback because he is openly gay,

29:14and people accused him of agended.

29:18I didn't say gendered, I said agended science.

29:21Yeah, that he was part of some conspiracy, a gay agenda to force Americans to

29:28regard people with same -sex orientation as somehow okay.

29:32But a replication of the study from an independent group that presumably has no reason

29:38to be biased whatsoever. Well, they were very skeptical of it.

29:41So that was William Blyer, who eventually, and there's an interesting aspect of it.

29:47It took him a long time to get a sample big enough because, you know,

29:51Simon, it was such a horrible time in AIDS epidemic.

29:56There were so many young men dying that Simon had no trouble finding enough brains

30:03to do the sample. And then as treatment got better, the death rates of HIV

30:09started going down. And so it took longer for William Blyer to gather the samples,

30:14but eventually he didn't. And even though he was skeptical of it, he saw it

30:17too. The question about AIDS, I mean, Simon was able to address that in that

30:24he also had some straight men who had AIDS, and he didn't, you know, they

30:29weren't significantly different from other straight men.

30:33And so it was widely interpreted as proof that sexual orientation is not a choice,

30:39that it's something that happens to you.

30:41And of course, I don't think sexual orientation is a choice.

30:44That's true. But Simon himself made it clear that he could only look at this

30:50nucleus in adults, right? You can only look, it's so tiny.

30:55The sexually dimorphic nucleus, the preoptic area in humans, it's about the size of a

30:59grain of sand, right? So you got to have a microscope and you can only,

31:03there's no non -invasive way to look at it.

31:05And he pointed out that he didn't know if, what the order of causation was.

31:12He didn't know if those men had been born with a smaller SD and POA,

31:15and that's why they became gay.

31:17Or did something else cause them to become gay and also cause the SD and

31:23POA to get smaller? And for the public, the idea that a nucleus might change

31:27its size in adulthood, maybe that seems kind of like, you know, unlikely.

31:32But as neuroscientists, we know, you know, that adult brains are changing all the time.

31:39In fact, even in animals, Brad Cook showed that, you know, there's a nucleus, the

31:43medial amygdala. There's sex difference there, but if you take away the testosterone in males,

31:50sex difference goes away in just a matter of a few weeks.

31:52So Simon's work on the SD and POA, also known as INA3.

31:59I won't bother with why.

32:00Unfortunately, I remember the full name because my brain, it's the interstitial nucleus of the

32:06anterior hypothalamus subregion. I'm not saying that to impress anyone.

32:09When you get to be 50, which I can now say that, you wonder why

32:13your hippocampus remembers certain things that are like basically totally useless to remember.

32:17I waste so many synapses on totally useless crap.

32:21But, but that's not, that's, that's, that's worth holding on to.

32:25You did well. So, but so, so we don't know.

32:30It's a chicken and egg problem.

32:31We don't know if, if that happened, if they were gay because they had a

32:36small INA3 or do they have a small INA3 because they're gay.

32:40So what, what I liked about it, what I liked about it, Dennis' otoacoustic emissions

32:44and is pretty good evidence that that happened well before they had a sexual orientation.

32:52And the other thing I always liked about it is that, well, I mean, you

32:57can't imagine there's a social influence on digital.

33:01And nobody knew about this.

33:04So I wasn't worried that there were some little girls out there that looked at

33:07their hand and say, hmm, gee, that looks kind of masculine.

33:09Maybe I should be a lesbian, right?

33:11Because nobody knew this. Until your paper was published.

33:14Yes. I mean, as I recall, there was some like schoolyard stuff of kids looking

33:19at each other's hands and trying to decide who was gay and who was straight.

33:22You know, every once in a while to this day on the internet, I'll look

33:26at them and there'll be a little ad over there claiming to tell me something

33:29about my personality based on digit ratio length.

33:34And it's just like, you know, please.

33:36Yeah, there's nothing to it.

33:38Don't waste your money, gang.

33:40And there's an aspect of this, this fact that the group differences were there, but

33:44you can't tell about differences between individuals that I think is the hardest thing for

33:49scientists to communicate to the public.

33:51Yeah. You have a really good way of explaining this to people because, and it's

33:55an important lesson just in reading statistics and making sense of data that I'd love

34:02for you to give an example of how this plays out at perhaps in a

34:06separate example. Psychologists, they like to talk about a way of measuring how big a

34:10difference is between two groups.

34:12So this difference in digit ratios between men and women, it's, it's a relatively small

34:18difference. It's like, well, we measure it in terms of how many standard deviations apart

34:23are the two means of the populations.

34:25The two averages. The two averages.

34:27And to give an example of that, everyone knows about the sex difference in human

34:31height, right? And among adults.

34:33So that's a huge sex difference.

34:35It's one where we're all aware of it.

34:37And if, if nobody had told us it was such a thing, we'd notice it

34:41after a while. Right. And that, that's because those two averages and those two populations

34:46are about two standard deviations apart.

34:49The standard deviation being a measure of how much variability there is in something.

34:54So that's a huge sex difference.

34:57And to give you an idea of what that means, if I had you grab

35:02a sample of a thousand people, and I'm going to tell you one thing about

35:05each one of them, and that's their height, that's all.

35:08And now I give you the job, you've got to guess what sex they are.

35:12And I can tell you what you want to do to maximize your hit rate.

35:16Everyone who is five feet, five and a half, you're going to say those are

35:20men. And if they're less than that, you're going to say they're women.

35:23And you'll be right about 80 % of the time, which means you'll be wrong

35:29almost 20 % of the time.

35:31Right. And so everyone, you can, you can see that, that there's some predictive power

35:36there, but not, it's far from perfect.

35:40Well, this sex difference in digit ratios is half a standard deviation.

35:46So a quarter of that.

35:48And so that means there's much more overlap.

35:50And that, and, and we know that other things influence digit ratios too, not just

35:55prenatal testosterone. And so this is why there's no predictive value.

36:00I mean, so anyone who looked at their hand while we were talking about this

36:03and got worried, I don't know anything about your particular prenatal testosterone level, no matter

36:10what your digit ratio is.

36:12What about bisexuality? People who identify as attracted to both men and women.

36:17And maybe we ask about first bisexual women, then bisexual men.

36:21Is there a pattern in digit ratios that leads anywhere?

36:24I mean, in those days, we didn't have enough people that identified as bisexual to

36:29have a reasonable sample. And it's interesting.

36:31And that's something that's changed, right?

36:33I mean, if you do surveys now, especially for among younger people, there are more

36:36people who report that they are bisexual than there were then.

36:40So, so I don't really have anything to say about them.

36:43The one thing I will say is I'm sure that even among lesbians, there's more

36:47than one pathway, more than one developmental pathway to, to, to become a lesbian or

36:52to become a gay man, right?

36:53I don't think there's just one thing.

36:55That's not how human behavior.

36:57But you do think it's based on the data that it's biological.

37:00Based on that data, I think testosterone has a say, right?

37:03That it doesn't mean it's the whole package.

37:07Prenatal testosterone. Prenatal testosterone. And the reason I ask that is, I mean, there are

37:10conditions that are not uncommon where, um, someone has a particularly stressful long phase of

37:17development where there's every reason to believe that their androgens are impacted negatively.

37:24Yes. There's also every reason to believe that there are stretches of development where androgens

37:29are increased. Like we know that people who do a sort of a contact sport,

37:35um, or engage in anything that requires some like deliberate aggression.

37:41I realized that real martial artists, no competitive aggression, know how to, you know, sort

37:45of, um, gate their levels of aggression so that they're not, they're not like in,

37:48in a fury. Right. Um, like, but we know that certain types of activities, competition,

37:55et cetera. I mean, there's no question that those can increase androgens.

37:59So you can imagine there's some plasticity postnatally and that could be before puberty.

38:05It could be during puberty.

38:06And, and so that's testosterone.

38:09They're the. Adi, as you said, you said something that even as a developmental neurobiologist,

38:13I don't think I'd ever heard stated so clearly, and it's so important that the

38:19rate of brain development from birth until age 12 is at least as fast as

38:25it was before we're born.

38:27Yeah, I mean, the way to really bring that home is to compare human brain

38:32growth and chimpanzee brain growth.

38:33So, up until birth, the rate at which the brain size increases compared to body

38:40size is about the same in humans and chimps.

38:44And shortly after birth, the chimpanzee brain stops growing as fast and eventually asymptotes right

38:51away. The human brain continues that feverish fetal rate of growth until at least six

38:57years of age, maybe out there to 10 years of age.

38:59So, people have pointed out that in a real sense, human beings, children are fetuses

39:07that are outside learning a whole bunch of stuff from other people.

39:11That's the real distinctiveness of our species is, you know, we have this protracted childhood

39:18and really intense social learning.

39:21And as you say, a fetal rate of growth, even though we're not in the

39:24fetus anymore. So, I guess for me, the idea that behavior, exposure to things, you

39:30know, and I don't want to get into valence of negative, positive, but sure, pesticides,

39:35but also, you know, schoolyard activities.

39:39If you have, and we'll get to this, you know, five siblings, and it's very

39:43competitive, who gets how much pizza?

39:45You know, I had one sibling, so it was a little bit, you know, there

39:47was competition, but it was different, right?

39:49You know, these things change hormones, hormones change the brain.

39:54The brain, as you're explaining, can impact sexual preference.

39:58What's great about studying hormones and behavior, right, is that sometimes you can control the

40:02hormone in animals, at least.

40:04But the hard thing about hormones and behavior that people don't understand is that behavior

40:09can affect hormones, as you say.

40:11In competitions, the winners afterwards are more likely to have higher testosterone and the losers

40:17will have lower. In elections, it's been shown that people whose candidate won the presidential

40:23election, their testosterone levels went up a little bit, and the people whose candidate lost

40:29went down a little. And so you'll always have this cycle where the hormone alters

40:34the behavior, and then the behavior alters the hormone, and you always have to look

40:38for ways to try to pin down the order of effects.

40:44And, you know, not always easy.

40:47The only thing I know for sure is that the brain remains plastic all of

40:51our lives. Well, that statement is a significant one because I also believe that the

40:56brain remains plastic throughout our lives.

40:58It's always surprising to me that the hypothalamus remains plastic throughout our lives.

41:03And I think that's worth perhaps double -clicking on, so to speak.

41:07Because, you know, the idea that you can learn another language and your neocortex changes,

41:12or you can learn to juggle and your, you know, your neocortex, your motor cortex

41:16changes, your cerebellum changes. Okay.

41:18Like, there's a lot of beautiful studies demonstrating that.

41:20But when I think about the hypothalamus, I think about it as something that's pretty

41:26hardwired by time puberty wraps up.

41:30But the more I learn and the more data that get published, the more surprised

41:35I am. I saw a paper just the other day that the neurons that control

41:39suppression of appetite, these POMC neurons in the arcuate nucleus, there's a population of them

41:44that are sort of differentiated that can become, let's just call it, pro -hunger by

41:49expressing a different peptide, neuropeptide Y.

41:52And that there's a lot of late -stage plasticity.

41:54And this may explain why people who reach a certain level of obesity may actually

41:58find that they're hungrier despite not needing food.

42:01So it's fascinating to me how these deeper brain structures may actually remain plastic.

42:06I think both your statements are true.

42:07I think it's probably true that the neocortex is more plastic than the hypothalamus, but

42:12it's a matter of relativity.

42:13And so as you say, the one thing we know is that there's plenty of

42:17plasticity there. The other thing I noticed, so I've gone to society for neuroscience meetings

42:23pretty regularly every year since 1977.

42:26And after a while, I noticed something.

42:28Every year when I went to the neuroscience meeting, the brain was more plastic than

42:32it was the year before, right?

42:33I mean, because there are more and more of these demonstrations.

42:36And it's like, you know, I think synapses can come and go just about anywhere.

42:41And so hardwired, well, let's say there might be less plasticity in the hypothalamus.

42:48Surely so. But that doesn't mean there's none.

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44:16What are some of the other effects in human studies of behavior impacting hormones that

44:23come to mind for you?

44:24I mean, it's been a while since we've touched into this, and we haven't done

44:27it much on this podcast.

44:28I mean, obviously competition, winners, losers, you explained the data there.

44:32What are some other scenarios, just studies that have been striking to you or that

44:37have stood out over the years?

44:38I think for testosterone, I think the big ones have been, have been competition, you

44:44know, between males. Um, and no, I don't, you know, I mean, there, there's a

44:49stress response, but that's a whole other thing.

44:51What about sex behavior itself?

44:53In animals, at least, we know that, that there's a relationship there, that, that in,

45:00in males, in males of most species, let's take rats, uh, if you take away

45:04the testosterone within a few weeks, they'll, they'll stop mounting altogether.

45:09And if you give them testosterone after a few weeks, they, they start mounting again,

45:14right? So we know that that, um, plasticity is, is there, and we know that

45:18it's driven by testosterone. But, uh, in, in animals where they're in charge of their

45:23own testosterone, we've known for a long time that if a male is exposed to

45:28the odors of a receptive female, that causes a spike in their testosterone.

45:34And so, uh, that's kind of preparing them for maybe, maybe some, maybe I'll be

45:39lucky. Maybe there's something coming down the pike.

45:42Uh, and so we know that that's a reciprocal relationship, uh, when the animal's in

45:47charge of the, of the hormone.

45:49For the longest time, thanks to your textbooks.

45:52And by the way, folks, uh, Mark has, um, authored some of the most important

45:56textbooks on hormones and behavior, developmental neurobiology.

46:00I mean, he's a, he's a true scholar of the whole field.

46:02And so I'm immensely grateful to him that those textbooks have formed the backbone of

46:06a lot of, uh, solo episodes of the podcast.

46:09So, um, you know, the textbook version of male versus female sexual behavior has been

46:17a story about females having a circuit that goes from brain to body to control

46:24this thing they call lordosis, the arching of the lower back, the receptivity, the willingness

46:29to mate. And the males having a circuit that goes from brain to spinal cord

46:34to body, um, involving, uh, arousal, erection, mounting, um, insertion, ejaculation.

46:42I mean, your lab and others has really parsed this, uh, right down to the,

46:46the details. And yet, of course, people have sex that way, but also other ways.

46:53And so for a lot of people who aren't familiar with hormones and neural circuits

46:57and behavior, the sort of strict context kind of is, is still forms the framework,

47:03you know? I mean, I, I've learned, and I'm now fortunate that this podcast has

47:08been around more than five years, so I no longer have to tap dance around

47:10things, right? So people will say, oh, well, you know, there's this lordosis behavior in

47:14the female. She's, she's receptive, um, or not.

47:18Um, he mounts, et cetera.

47:19And then there's gay men who have to have sex a certain way that mimics

47:22the female sex pattern of behavior.

47:24And so people do this one -to -one, right?

47:26Yeah. And I think that it's understandable why they do that if they're not educated,

47:31but how should we make sense of these biological circuits that are in the textbooks

47:35that define stereotyped, literally motor behavior?

47:39It's almost like saying, like, like females have sex this way with males.

47:43Males have sex this way with females, but then the caveat is always like, oh,

47:47but in humans, all that goes away.

47:48And there's these like bonobos that are a little bit more like humans.

47:51So did we waste all our time, um, studying that stuff?

47:55I mean, really. And you're getting at exactly what every textbook author has to deal

47:59with, right? Which is, you know, uh, as the old joke go, you, you, you,

48:04you look where the light is, right?

48:06So we know so much more about the circuits that are involved in the motor

48:11behaviors because they're relatively easy to trace and relatively easy to manipulate and relatively easy

48:17to, to study. We know lots about the motor patterns in animals.

48:22We know a lot less about the motivational patterns in animals, which in human sexual

48:29behavior is, I mean, in many ways, that's the whole show, you know, that's, that's

48:34really what's, uh, and, and we don't really have good animal models of, of libido,

48:40right? And this was brought home to me many years ago.

48:44Now I, I was on a session of 60 Minutes, the CBS news program, and,

48:50uh, Leslie Stahl was there in our lab.

48:53I mean, the producers had called me up and said, you know, can you show

48:56us a way that, that early testosterone exposure changes behavior permanently?

49:01And I said, sure, I can do that.

49:03Give me some time. So, I.

49:05I went to the lab and castrated a bunch of rats on the day of

49:09birth. I know how to do that.

49:10I'm not proud of it, but I know how to do that.

49:13And they came three months later.

49:17And so I showed them those motor patterns you talk about.

49:21So here's a typical female.

49:23I've given her hormones, estrogen, progesterone, so I know she's going to be receptive.

49:27And here's a male rat that I know has had lots of experience copulating.

49:33And Leslie immediately dubbed him Romeo.

49:36Okay, well, this is Romeo.

49:38And she hates rats, by the way.

49:40She was very brave. So I drop a female on top of Romeo, and he

49:45starts mounting, and she shows the lidosis posture.

49:47It's all beautiful and easy.

49:49And we do that several times.

49:50I said, now I'm going to drop a male, a control male in.

49:55And Romeo, of course, you know, you don't know unless you try.

49:59He mounts several times, and the male rat acts like nothing's going on.

50:03I mean, it's just a bored thing on earth.

50:05And Romeo eventually gives up.

50:08Now I drop into the cage of a male rat who I castrated on the

50:13day of birth, 90 days before.

50:15And I've given him the same hormones I gave the female to make her receptive.

50:21Romeo hops on, and sure enough, a beautiful lordosis, right, of the sort that the

50:26control male never showed. So here this neonatally castrated male is showing very female -like

50:34patterns. And Ms. Stahl kept asking me, would you say this is a gay rat?

50:42And it's, you know, I'm sitting there, and I'm definitely in a tough spot because

50:45I don't think my rats have an orientation.

50:48I mean, we just saw Romeo happily mount any rat I threw in the cage

50:53because what do you know?

50:54You know, try your luck.

50:56And so, you know, she asked me several, and I knew she wanted me to

51:00say that, but I said, what I would say, I don't remember exactly what ended

51:04up in the final. What I would say is this is a rat whose sexual

51:08behavior has been permanently changed because of something that happened to him a long time

51:14ago at the very beginning of development.

51:16And really that's the best I can do in terms of any rat model of

51:22sexual orientation. I don't think my rats have a sexual orientation.

51:25If I give the female those hormones, she's going to show oridosis to whoever mounts

51:30her. And my male rat, he will mount any rat he comes across just in

51:34case he gets a oridosis out of them.

51:37Well, good on you for not getting corralled into giving a particular answer.

51:44I've recently joined CBS as a correspondent.

51:46If we have this conversation on 60 Minutes, I promise to not try and force

51:50an answer. Romeo is an interesting case because I think for most people, including myself,

51:58I thought that you were going to say that Romeo was willing to try to

52:03mount a female. If she was receptive, he would mate.

52:06If not, he wouldn't. But I was surprised that he would try to mount a

52:12male as well. That doesn't align, at least with my experience, of male human behavior.

52:18Certainly not. That's right. This is the thing that's distinctive about humans is we're not

52:23actually that particular about what particular behaviors we engage in, what motor behaviors.

52:29And we're overwhelmingly interested in who our partner is.

52:32That is an overriding concern that I don't think my rats have.

52:38I think few animals do.

52:40Here's the... You're the anthropologist from Mars, and I tell you, here's a person that

52:4950 %... Here's... Whoever's the sexiest man alive this year, People magazine.

52:54I don't know who that happens to be.

52:56Well, this is an interesting discussion altogether because there's this...

52:58People have been lining up the images of these people and claiming that they're sort

53:02of like this effeminate drift that takes us back to a time in the early

53:0890s when there was this sort of revision about male facial...

53:11Fascinating. We can get back to that, but yeah.

53:13Okay, okay. It's not... The point being that it's not fixed.

53:16Yes. Yeah. Well, whoever... Let's say it's George Clooney.

53:19So here's someone that half the planet believes is an ideal sexual partner, right?

53:27But the other half of the planet finds him totally unacceptable, even if the behaviors

53:34they engaged in would be pretty much the same.

53:37And so, you know, in terms of positions and who's doing what to whose genitalia,

53:44et cetera. I mean, for most people, it isn't that there has to be one

53:49particular act, I suppose there's some, but for most people, there may be a variety

53:53of acts that they want to be engaged in with that other person.

53:57And their overwhelming concern is the gender of that other person or the sex of

54:02that other person. You know, it's hard to have an animal model of that.

54:06I actually do know of one example in sheep, if you want to talk about

54:12this. Of all things. Yes.

54:14Oh, I noticed. So Chuck Roselli out at Oregon, he's the one that studied this

54:20very carefully. I guess shepherds have known for ages that in any herd, there are

54:26some rams who will not mount a female ever and keep mounting other males.

54:33And, of course, to maintain a herd, you don't need every male to reproduce.

54:41But in the old days, those males got sent off to slaughter, right?

54:45Well, hearing these rumors, Chuck did these tests where he would put a bunch of

54:55females that are in stocks so they can't move and they're all ready for mating.

55:01And he put a ram in with them.

55:04And most rams, of course, will mount the females.

55:07He puts in these rams that prefer males.

55:10If there's a variety of sheep's butt sticking out at him, he'll mount males, including

55:18sometimes having intermission through the anus and all the way to ejaculation.

55:24And he never mounts a female.

55:27In some cases, they'll have one of these, I'm going to call them gay rams.

55:32I think they have an orientation.

55:34He'll put this gay ram where there's a dozen females.

55:37And he might be in that paddock for 12 hours and never mount a single

55:42female. Highly unusual for male rams.

55:44And these are not typical rams.

55:46It's like a small percentage of the population.

55:49And I don't know how to explain that.

55:52I mean, you would think that these gay rams that, well, you know, an ejaculation

55:57is an ejaculation, right? An orgasm is an orgasm.

55:59I presume they have orgasm.

56:00You would think that at some point, well, there's nothing else to do in here.

56:04I'll mount one of these ewes.

56:05And they never do. And I don't know how you can explain that except that

56:09there's some aversive component that rams do care about the sex of their partner.

56:17And that for these gay rams, there's some aversive component to that.

56:22By the way, Chuck told me not too long ago, there's a company that has

56:28identified these gay rams and decided that instead of sending them off to slaughter, they're

56:34going to harvest their wool and sell them and make them into clothing.

56:38So you can buy wool clothing that came from gay rams and know that you

56:45saved them from the slaughterhouse.

56:47There's no response that's appropriate to that statement.

56:50And apparently, you know, they're out of stock.

56:53So it's been a big success.

56:55Actually, I can think of about 50 different responses to that, none of which are

56:59appropriate or have any real conceptual importance.

57:04So I won't say. Fascinating because rams, while, of course, they have sociodynamics, presumably there

57:14isn't pressure independent of reproductive pressure to be a gay ram or a straight ram.

57:22And I guess I left off the kicker, which is Chuck eventually dissected the preoptic

57:28areas of these various rams.

57:30And he found a difference between the preoptic area of gay rams and straight rams,

57:35a difference in how they process testosterone.

57:38And exactly that part of the brain, the preoptic area, where Simon saw a difference

57:43between gay and straight men.

57:45So there may be something about the hypothalamus, the preoptic area, that has something to

57:52do with orientation. If we're talking about an organism as complicated enough to have an

57:56orientation, including sheep. This is a particularly nice moment, not just for this episode, but

58:05for the entire podcast arc.

58:08Because there are these moments that come up every once in a while where a

58:13larger principle shows up in a new way that I think is really important for

58:19people to understand. Across neuroscience, we see this push -pull, right?

58:24A flexor muscle like the bicep, when it flexes, the tricep relaxes.

58:28When the tricep flexes, the bicep relaxes, these antagonistic relationships.

58:32You see this in the hunger circuit.

58:33I mentioned one earlier. Like hunger and feeling full, they're like a push -pull.

58:38They're like a seesaw. And you see this over and over and over again.

58:43It's a very consistent theme of brain function.

58:46And you said something that I was not aware of, but makes perfect sense.

58:50I just wasn't aware that there were, you know, data at the level you described.

58:55Which is clearly there's an appetitive aspect to sex behavior.

59:01Heterosexual males wanting to have sex with females.

59:03Heterosexual females wanting to have sex with males and so on.

59:07Every derivation there. There's a desire.

59:09In species where there's strong pheromone and odor determination and receptivity stuff gets played out

59:16that way. It looks one way.

59:18In humans, it may have some of that, but it plays out a different way.

59:20Receptivity is communicated differently. Although odor may be very important in ways we don't quite

59:26fully understand. But this idea that there's an aversive aspect to it, right?

59:32I think this is important and it's something that I have not heard discussed before.

59:35And I think that sociologically it has relevance because I think that there's so many

59:41different aspects to the notion that our species, humans, humans, come in gay and straight

59:48and perhaps bisexual varieties. We know that's true.

59:51Clearly. But there is this not uncommon theme whereby many people, I can only, you

1:00:00know, say. We know the meaning of a human being.

1:00:01many people, right, not all, that the concept of mating with same sex is aversive

1:00:07to them. And that has shaped a lot of the landscape around this.

1:00:12And I'm not trying to get political here.

1:00:13It's just, I think it's worth acknowledging that that may be a real phenomenon too.

1:00:19I'm not trying to justify mistreatment of anybody, but I think that we're never going

1:00:24to get where we want to go as a species, societally, until we really at

1:00:28least understand the biology and how to work with it.

1:00:31And so the idea that same sex sex, right, would be aversive as an idea

1:00:40to people. Some people are like, oh, well, they haven't been educated.

1:00:43Okay, perhaps, you know, but there may be a biological basis for that.

1:00:48I think the data is still out, but I think it's, to me at least,

1:00:51it's pretty clear that for men at least, there's an asymmetry here.

1:00:57That experiment where I said, you know, who wants to have sex with George Clooney?

1:01:02Half the population says, sure, the other half population, never.

1:01:06If we reverse the experiment, what percentage want to have sex with Margot Robbie?

1:01:10And yeah, half the population, the men would see her as a very desirable sexual

1:01:16partner. But, you know, the women too would, many women would also at least consider

1:01:24the idea of having sex with her.

1:01:27And we know there are plenty of women who are straight in one part of

1:01:31their lives. And later, they fall in love with a woman, and now they feel

1:01:37like they're gay, right? So females, women, are more plastic in terms of their sexual

1:01:46longings and sexual orientation than men are.

1:01:50I'll be a little more specific.

1:01:52I think it's among males, where sometimes, for many males, not all, there's an aversive

1:01:59idea that the idea of having sex with the same -sex partner is aversive.

1:02:04Now, of course, context matters, right?

1:02:07There's same -sex happening in prisons all the time when, you know, if the conditions

1:02:11are enough. And I don't know where that aversive component came from.

1:02:17It could be that our society, maybe it's all socially inculcated, you know, again, before

1:02:23we're aware of it at all.

1:02:25But I think there's also at least the possibility that there's a biological component to

1:02:30it. And I think that's what Chuck was getting at, in that here's this difference

1:02:34in the brain. He doesn't know when the difference happened in the pre -optic areas.

1:02:39But it seems to correlate with this idea that maybe these gay rams, no, they're

1:02:45not interested in having sex with her.

1:02:48It's aversive to them. It's aversive, yeah.

1:02:51There's no other way to, I can't, I don't know any other way to explain

1:02:54how they choose never to, never once mount a female.

1:02:59I feel like that the acknowledgement of a, the aversive pathway for sexual partner choice

1:03:08is as important as the acknowledgement of biological correlates of homosexuality.

1:03:15Yeah. Because if this sort of conversation is ever to advance past the sort of

1:03:20like, okay, what's okay to say now that we're willing to say now, trust in

1:03:24science disappears. I really believe that.

1:03:27Now, of course, the problem is that people leverage fragments of what they hear in

1:03:32order to make arguments in, in favor of whatever stance they have.

1:03:36And that's the complication. That's why I like long form because no matter what gets

1:03:39pulled out, we can go back to the full conversation.

1:03:42Right. And this makes you old fashioned because this, that's not the world.

1:03:45I mean, our world seems to be hurtling towards this.

1:03:48Yeah. Yeah. I mean, world of snippets.

1:03:51People will notice that we have not used the word gender.

1:03:54We're talking about biological sex and sex, the act.

1:03:57And we're talking about male versus female partner choice.

1:04:01And we're talking about a desire for one or the other and an aversion to

1:04:07one or the other. And I think the aversion piece is an important theme.

1:04:10So here's a hypothesis. If I can come do a sabbatical, I'm due for a

1:04:14sabbatical at some point. It may be that in male humans, that there's a pathway

1:04:20or a molecule that serves as an aversive to sex with other men circuit, peptides,

1:04:29neurons, et cetera, that suppresses, um, sexual desire and activates some level of disgust.

1:04:35I'm going to just say it bluntly.

1:04:37Might not be the same disgust that they would experience to something more aversive, but

1:04:40okay. And that in women, there is no such pathway.

1:04:44There's either desire for women or desire for men.

1:04:49But as you said, you know, statistically, women are more open on average to same

1:04:57sex interactions. And it may be because there's no aversive signal or the aversive signal

1:05:05has a less robust circuit.

1:05:06To me that, that would explain these differences, that these sex differences in who people

1:05:11are willing to have sex with your hypothesis fits the data.

1:05:15I mean, it is true that in the, like the early nineties, for instance, when

1:05:19the first gay characters were on television, like the real, first real world, and I'm

1:05:23really dating myself here, and subsequent characters started to dismantle some of the stereotypes.

1:05:28that had been seen in like comedies in the 80s and things like that of

1:05:33the effeminate gay man, right?

1:05:34What you saw was indeed that heterosexual women, as far as we know, seem to

1:05:43be more like generally accepting of gay men before heterosexual men embrace that as typical.

1:05:51That's my impression too. I think it's pretty clear.

1:05:53Yeah, and then there's a societal shift and then it sort of becomes like, like

1:05:58if you, like I spend some time on X, formerly known as Twitter, right?

1:06:03And there's some gay political accounts and you just kind of notice, like it's just

1:06:09people are like comfortable with it.

1:06:12Men and women seem to be comfortable with that, right?

1:06:14I mean, of course, you don't see a lot of attacks now.

1:06:17That's very different than what you would have observed, would have observed, for instance, in

1:06:20like the late 80s, early 90s, right?

1:06:23Anyway, I think these are important biological, biological phenomenon, this notion of an aversive pathway.

1:06:30You could imagine where societal standards or community standards or household standards might, you know,

1:06:38amplify or reduce, like the sort of expression of these things.

1:06:43I'm sure they do. Yeah.

1:06:44And I'm sure, you know, cultures, you know, can amplify or reduce that component.

1:06:52The question is, you know, to what extent?

1:06:54I mean, and I don't think we know.

1:06:57One thing that we haven't talked about, and it is a small percentage of people,

1:07:00but it's something that people think about, is this notion of sort of neither here

1:07:07nor there, kind of mixed sex, right?

1:07:10Is there a biological correlate of that?

1:07:14A graduate student my year, when you were my professor, Nikki Osipka, Nicola Osipka, who

1:07:21was already famous for training dogs for the Beastmaster show, which is amazing, and had

1:07:29very well -behaved dogs that she would bring everywhere with her, studied a species of

1:07:33mole in Tilden Park that could trans -differentiate its testes into ovaries and back again.

1:07:41And I thought, well, that's like alien, weird levels of stuff.

1:07:45But she would occasionally go over to UCSF when babies were born that were sort

1:07:50of, back then they called them, no one uses this language now, pseudo -hermaphrodite.

1:07:55Yes. What is the deal with exposure to prenatal androgens and neither clearly here nor

1:08:01there a genitalia? Yeah. So in most of those cases, we're talking about congenital adrenal

1:08:08hyperplasia, also known as CAH.

1:08:11And the congenital means it's present at birth.

1:08:13And the adrenal hyperplasia is referring to the fact that the adrenal glands are slightly

1:08:18larger. And the reason they're slightly larger in this case is because these are individuals

1:08:24where the fetus itself is not able to make some of the adrenal steroids that

1:08:31are important for staying healthy.

1:08:33And so the brain detecting, hey, where are the adrenal steroids that we need here,

1:08:40drives the pituitary to tell the adrenal gland, hey, we need more steroids.

1:08:46The adrenal gland gets the message, it hypertrophies, but the machinery isn't there to make

1:08:51those steroids. And so instead, the adrenal gland makes testosterone and other androgens.

1:08:59Actually, this can happen in either XX or XY individuals.

1:09:02And in XY individuals, people might not notice.

1:09:07But in XX individuals, what that means is that prenatally, her genitalia are being exposed

1:09:15to more testosterone than is typical.

1:09:17And so under the influence of this extra testosterone, the clitoris may grow to be

1:09:24bigger than the typical clitoris.

1:09:27In some cases, in extreme cases, the phallus looks like a penis.

1:09:33And the skin around that area that would normally form the labia, again, there might

1:09:38be enough testosterone that it starts to look like a scrotum.

1:09:41Except, of course, there are no testes inside there because this is an XX individual.

1:09:45So these individuals are identified at birth, typically, especially in XX individuals.

1:09:53And there's an easy treatment, which is, oh, they can't make, you know, you do

1:09:58the test, and you say, oh, they can't make adrenal steroids, so we'll give them

1:10:02some. And so for the rest of their lives, they take adrenal steroids orally and

1:10:06get the benefits of that.

1:10:08And that shuts off the hyperactive adrenal glands.

1:10:12So it shuts off the role of the output of testosterone.

1:10:17So this is what's known as an intersex phenotype.

1:10:20And yes, you're right. In the older literature, they were sometimes known as pseudo -hermaphrodite,

1:10:26huh? With the idea being whether a hermaphrodite is an individual that can function and

1:10:32reproduce, either as a male or female.

1:10:35And so supposedly, they were pseudo because they can't do that because they have only

1:10:39ovaries. Well, you can imagine, first of all, being called hermaphrodite, nobody liked that.

1:10:47And if you ask them, well, is it better if I put this pseudo at

1:10:50the beginning, does that make you feel like you're being less stigmatized?

1:10:53No. But a much more accurate...

1:10:56description is to say that it's intersex.

1:10:59They have a phallus that's somewhere between a clitoris and a penis, and the skin

1:11:04around there is sort of like a scrotum and sort of like labia.

1:11:09So in the old days, once this got recognized, it was standard procedure to tell

1:11:18the parents, oh, this is an emergency.

1:11:21We need to do cosmetic surgery.

1:11:23We need to do surgery to make this little girl look like all the other

1:11:27little girls. You know, sometimes this surgery was, you know, there could sometimes be successful

1:11:32or not. And indeed, they knew how to make her look like other girls.

1:11:39But many of those intersex folks, when they grew up, were pretty angry that someone

1:11:45had done this surgery on them that wasn't needed medically, right?

1:11:49They were already taking care of the problem with the exogenous adrenal steroids.

1:11:54And so who asked you to deal with my, you know, to do surgery on

1:12:00my clitoris? In some cases, the tip of the clitoris was missing.

1:12:03And so these women grew up and were anorgasmic because they couldn't get the stimulation

1:12:09that they normally would have had.

1:12:10These days, there's much more, thanks to the activists like Cheryl Chase and others who

1:12:18started getting the pediatrician's attention.

1:12:20Hey, you need to think about that.

1:12:22You're doing elective surgery on an infant who cannot possibly have informed consent.

1:12:28And so these days, it's more of a wait and see attitude, which I think

1:12:31is absolutely. So wait till they're grown up and ask them then if they want

1:12:36to have surgery. And my guess is most will say no.

1:12:40I think that's been the pattern so far.

1:12:43So these are females who were exposed to more testosterone than other females.

1:12:48So does that mean that they're going to be attracted to women when they grow

1:12:53up? And the answer is, well, interestingly, if you look at groups of women with

1:12:59CAH, they are more likely to be same -sex attracted to be lesbians than the

1:13:05population at large. But most of them are straight.

1:13:07But what's interesting about that is the older they get, as you keep surveying them,

1:13:13the higher the percentage of them report having a lesbian orientation.

1:13:18So it's possible, first of all, that indicates that, yeah, maybe prenatal testosterone increases the

1:13:25odds of them being lesbians when they grow up.

1:13:28And you also wonder, well, how many of them always had that same -sex attraction,

1:13:33but, you know, we're following the pathway society laid out for them.

1:13:38And then as they get older, they say, well, no, screw this.

1:13:42I, you know, I know who I'm attracted to.

1:13:44I don't have to fit the heterosexual mold.

1:13:46And so it's, you know, that's entirely consistent with the idea that prenatal testosterone makes

1:13:52you more likely to be attracted to women when you grow up.

1:13:55There's another syndrome that I know you've talked about, which is androgen insensitivity syndrome, sometimes

1:14:02abbreviated AIS. And it turns out the gene for the andro receptor that responds to

1:14:08testosterone and other androgens is on the X chromosome.

1:14:11And it may sometimes be that a woman will have an X chromosome that has

1:14:16a copy of the andro receptor gene that doesn't work.

1:14:20And if she passes that X chromosome onto a daughter, then she's sort of duplicated

1:14:26herself. What's interesting is when that X chromosome is given to a son, in other

1:14:31words, that egg with an X chromosome that has a dysfunctional copy of the andro

1:14:36receptor gene, if it gets fertilized by a Y bearing sperm, now we have an

1:14:39XY individual. And as you've explained clearly in your, in your basics podcasts, we know

1:14:47what will happen in development.

1:14:49The Y chromosome will mean that the indifferent gonad will develop as testes.

1:14:53The testes will secrete two hormones that are going to guide sexual differentiation in the

1:14:58periphery, one of them being anti -malarian hormone, which is going to suppress the development

1:15:04of the malarian ducts, and therefore no oviduct, no uterus will form.

1:15:10And the testes will also release testosterone, which normally would masculinize the body.

1:15:14But in this case, because there's no functional andro receptor to respond to it, the

1:15:19testosterone goes round and round, but the body doesn't respond.

1:15:22And so the Wolfian ducts don't develop.

1:15:25The periphery looks like a typical female.

1:15:29And these individuals, when they're born, often are not identified because the baby's born.

1:15:36The doctor does that very careful analysis by looking between the legs and says, congratulations,

1:15:41you have a girl. And they grow up to, to be girls undetected.

1:15:47And they come to a doctor's attention when puberty happens and all their classmates are

1:15:54having their period, but she's not.

1:15:57And so she'll eventually go to an OBGYN who will first do an exam, a

1:16:04vaginal exam. And he'll notice that the vagina is relatively short because the inner part

1:16:12of the vagina is normally derived from the malarian ducts.

1:16:15Well, in this woman, in this teenage girl, the malarian ducts never develop because of

1:16:21anti -malarian hormone. So I don't know.

1:16:24There'll be no cervix that can be seen in the exam.

1:16:26And if he takes blood plasma levels, he'll see that this very feminine -looking girl,

1:16:33teenage girl, has very high levels of testosterone.

1:16:36And presumably testes. And if he does a karyotype, he'll see that she has an

1:16:40XY karyotype. And yes, there are testes in there, typically in the abdomen.

1:16:45And they're releasing lots of testosterone because there's no negative feedback to tell the brain,

1:16:51you know, hey, you can stop sending signals to the testes now.

1:16:56In these cases, you can ask, well, what's the sexual orientation of these women?

1:17:01And the vast majority of them grow up to be straight.

1:17:04They are attracted to men.

1:17:06And they're often very interested in having a family.

1:17:09Of course, they can't carry children themselves, but they can adopt and things like that.

1:17:14And so they're very much feminine, very straight women.

1:17:19But they're XY. But they're XYs.

1:17:22So the question is, unfortunately, in terms of understanding whether prenatal testosterone alters our sexual

1:17:29orientation, these individuals aren't useful to us.

1:17:33Because we don't know if they're straight women because their brains could never respond to

1:17:39the prenatal testosterone. Or are they straight women because they were raised as girls and

1:17:44socialized to be attracted to men?

1:17:47It's a fascinating syndrome. And there's at least one woman with AIS who's self -identified,

1:17:52who's a successful model. And there's another woman who wrote a memoir that's quite good.

1:18:00And what's interesting about it, when there's no testosterone response, they have very feminine faces,

1:18:07very feminine bodies. And so they're, frankly, quite attractive as women.

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1:19:25I'm realizing, I'm drawing a model over here whereby we've got, again, accelerators and brakes.

1:19:33And I think we've got different axes.

1:19:38You know, I'm not trying to split hairs here.

1:19:41But I think for people who want to understand how hormones, sex, and behavior, sexual

1:19:46orientation fit together, it's very useful to think about, okay, you've got chromosomes that drive,

1:19:53you know, our typical notions of male versus female.

1:19:55And you're providing some important caveats where the body appears one way, but it's an

1:20:00X, Y, you know. And there's almost every derivation of this has been observed, although

1:20:05not at a very high frequency.

1:20:07And then you've got choice of same versus other in terms of orientation.

1:20:12A key role of prenatal testosterone there.

1:20:16Maybe some cultural or other types of plasticity that might be biased more toward the

1:20:22female side. It seems that way based on what you're saying.

1:20:26If I'm, you know, I'm willing to say it if you're not.

1:20:28It does seem that way.

1:20:30There's an aversive signal that kind of, that certainly in male sheep and other species.

1:20:37And that, you know, matches my observations as a 50 -year -old male who grew

1:20:43up in Northern California and, you know, I mean, again.

1:20:46In this era. And the joke being that I'm, I can only speak from my

1:20:49own reference point on this.

1:20:53And then we have a bunch of different things about partner preference and, and that

1:21:00at some point it almost seems like it departs from, well, it certainly departs from

1:21:06our sort of linear like, okay, uh, girls like boys, boys like girls, testosterone makes

1:21:12boys, estrogen makes girls, we're, we're, we're nowhere near there.

1:21:15We're, we're, we've left that station a long time ago.

1:21:18Um, and at the same time we arrive at a place where I think we

1:21:25need better languaging to separate these axes because it is very confusing for people.

1:21:31Um, and so that would be very useful if, if the fields of neuroscience and

1:21:36psychology would start to embrace the real world, uh, realities of, of, cause I actually

1:21:42think the lack of specificity of talking about orientation versus biological sex and, and these,

1:21:48and these other aspects have, have led, I think that's the source of a lot

1:21:51of. actually. Anyway, that's an editorial for another time.

1:21:57In terms of biological impact on sexual orientation, one of the more striking findings that

1:22:03you've been talking about for a number of years that just kind of shocks at

1:22:09first, but then you get a lot of nods from people, is this idea that

1:22:13the larger the number of older brothers that a male has, the higher the probability

1:22:20that he is gay? It's been seen over and over.

1:22:23I mean, it's really one of the rock solid findings in human sexuality that was

1:22:29first noticed by Ray Blanchard at Toronto and has been seen in many populations all

1:22:36over the world. So the way to emphasize the difference is if a baby boy

1:22:41is born today, if he has no older brothers, his odds of being gay when

1:22:48he grows up is about 2%, right?

1:22:50Pretty low. But if he had one older brother, his odds go up by a

1:22:55third. Okay, 2 .6. And if he has two older brothers, they go up a

1:22:59third again, right? Now we're at 3 .5.

1:23:02It turns out you got to have like a dozen older brothers just to have

1:23:05a 50 -50 chance from the same mother.

1:23:07Right. So we know that it's not, you know, in, you know, what they call

1:23:10now blended family or so this is...

1:23:12We'll get to those in a moment.

1:23:13But this is what you see.

1:23:15So you get a big population of men.

1:23:19Here's a big population that have one older brother.

1:23:22How many are gay? And it's a small number.

1:23:25And the number that have two, still small number, but more.

1:23:29And, you know, how do you explain that?

1:23:32We saw it when we did the surveys.

1:23:34We, I don't know if you remember, we also asked people how many older brothers

1:23:37and sisters they had and how many younger brothers and sisters they had.

1:23:41So it turns out in the general population, there are about 105 boys born for

1:23:47every 100 girls, right? That's also very consistent.

1:23:51105 boys born for every 100 girls.

1:23:53That's right. So there's, or put it another way, if you want, I can, I

1:23:58can guess the sex of any baby that's going to be born and I can

1:24:02be right more than 50 % of the time because I'm always going to guess

1:24:05boy, right? Because 51 % of the time, it'll be a boy.

1:24:09For straight men, you total up all the older brothers they have and all the

1:24:13older sisters. And there's a ratio of about 105 older brothers to a hundred older

1:24:19sisters. For the gay men, it turned out there were 140 older brothers for every

1:24:26100 sisters. Help frame that statistic for people.

1:24:30So, so you gave us the one older brother, what the probability was, right?

1:24:34It's a third increase. You go from 2 % to 2 .6.

1:24:37Is it a linear increase?

1:24:38As you increase the number of older brothers, do you just start increasing the probability

1:24:42at every with every older brother or are there, is it sort of a step

1:24:47function? It is in fact a linear progression.

1:24:49So at, at that rate, so Ray's worked that out.

1:24:52Of course, it's hard to find men that have had more than four or five

1:24:55older brothers, especially these days.

1:24:57But, but it turns out in the Kinsey surveys, Ray went to the Kinsey surveys

1:25:01way back then, you know, those, those interviews were incredibly thorough.

1:25:05And so they have a record of how many siblings of each sex, every one

1:25:09of those men had. And, and you can see it there too.

1:25:12And it's another one of these cases where I tell you this and you tell

1:25:16me, well, I know somebody who has two older brothers and they're gay.

1:25:20Is that why? Or I know somebody with three older brothers and they're not gay.

1:25:24Absolutely. Yeah. So you tell me, oh, I know someone who has two older brothers

1:25:27and he's gay. Is that why he's gay?

1:25:29And I really can't tell you, there's no way to know because in fact, most

1:25:35men with two older brothers are straight, right?

1:25:37Again, it's one of these instances where it gives you no predictive power about one

1:25:42individual, why they are gay.

1:25:44Ray Blanchard has done the statistics and their estimate is of all the population of

1:25:51gay men, about one in seven are gay because their mother carried brothers before them.

1:25:57And what I mean is those same men with the same genotype, same genes, if

1:26:03their mom hadn't had older brothers before them, they'd be straight today.

1:26:07Statistically speaking. Statistically speaking. But I, you know, you, you show me a picture of

1:26:11the, of the gay men's chorus and I can't point out which, which man is

1:26:15gay because of that, because there are other factors that can influence whether someone grows

1:26:20up to be gay. So again, it's one of these things where the statistical comparison

1:26:26is of great theoretical importance, even though it offers no predictive value for a given

1:26:33individual. So we know that males engage in much more rough and tumble play when

1:26:38they're younger, just like rats, just like monkeys.

1:26:41This is a fact. It's related to testosterone exposure.

1:26:45If a boy has older brothers, there's a decent chance he's engaging in more of

1:26:51that than if he has a sister.

1:26:53And given what you said earlier, that in humans, the brain continues to develop at

1:26:58a, at a massively accelerated rate, um, even after birth up to age six, testosterone

1:27:05has an influence behavior impacts testosterone.

1:27:08Okay. They're not in puberty yet, but you could imagine this has an impact.

1:27:12So the question, the experiment becomes for boys that had two or more older brothers,

1:27:18but were not raised with them.

1:27:19older brothers, does the effect hold of them having a statistically greater probability of being

1:27:26gay? It's a beautiful hypothesis, and you first hear about this, and that's the first

1:27:30thing you think. Well, maybe the younger brother got bullied, or...

1:27:34Or beat up his older brothers.

1:27:36Maybe the older brother somehow inhibited the younger brother from developing in a full masculine

1:27:40fashion. But it turns out Tony Bogart started looking at these data, and he started

1:27:47asking, well, what about stepbrothers?

1:27:49Do older stepbrothers make any difference in the odds of sexual orientation?

1:27:53And the answer was a clear no.

1:27:56On the other hand, older brothers who came from the same mother but were raised

1:28:01apart had just as much of an effect as those that were raised with us.

1:28:06So it does not seem to be socially mediated.

1:28:09In fact, Ray Blanchard and Tony Bogart have come up with a very plausible hypothesis

1:28:14called the maternal immunization hypothesis.

1:28:17And it runs something like this, that the first time a mother carries a son,

1:28:24that son is carrying some genes that her immune system has never seen before.

1:28:29All the genes on the Y chromosome, there's no way her immune system could have

1:28:34seen it. And as long as that first son is in utero, her immune system

1:28:41never sees it. But inevitably at birth, whether it's cesarean section or vaginal delivery, there's

1:28:47always blood and there's always mixing of blood.

1:28:49And so at that point, the mother's immune system is going to see these male

1:28:54-specific antigens that it's never seen before.

1:28:57Of course, it's going to regard it as an invader and it's going to start

1:29:00making antibodies to it. So their hypothesis is that each time a woman delivers another

1:29:06son, her immune system is going to generate more of these antibodies.

1:29:11And if she has a subsequent son, antibodies cross the placenta just fine.

1:29:16And so in fact, the placenta very actively sends antibodies across to protect the young.

1:29:22And so that would mean that her antibodies are going into this third son and

1:29:29somehow altering the development of their brain.

1:29:31And the strong evidence they found in favor of this is that in women who

1:29:37have sons where there's this pattern that looks like that might have happened, it turns

1:29:42out they have higher levels than control mothers of antibodies to a male -specific antigen,

1:29:50quite specifically. An antigen to a protein called neural ligand 4Y.

1:29:56So neural ligand... Cell adhesion molecule.

1:29:58Exactly. You know that neural ligands are important for synapse formation.

1:30:02And it turns out there's several copies, not unusual in humans.

1:30:06And this one, neural ligand 4, there's one on the X chromosome and one on

1:30:11Y chromosome, and they're slightly different.

1:30:14And so the fact that these mothers are making antibodies to this male -specific antigen,

1:30:21and that in their particular family, it looks like subsequent sons were more likely to

1:30:26be gay, you can imagine that's what's going on.

1:30:29That her immune system has perturbed the development of that subsequent son enough that when

1:30:35they grow up, they're more likely to be gay.

1:30:37Whatever the mechanism is, it has to be that it's the mother's body that is

1:30:42remembering how many sons she's carried before them.

1:30:45Right? And it's got to be the mother's body that somehow is doing something to

1:30:50perturb the development of her subsequent sons to make them more likely to be gay.

1:30:53It's a fascinating idea. And it also gets at that same theme that I mentioned

1:30:59before. There are lots of different developmental pathways to end up being gay or to

1:31:04end up being straight. And there isn't going to be one cause of anything in

1:31:09human behavior, and certainly not of sexual orientation.

1:31:12But I think the evidence is looking pretty strong that for women, at least, prenatal

1:31:19testosterone does have a say.

1:31:21And we know that in men, the mother's body has a say in whether they're

1:31:27going to be gay or straight when they grow up.

1:31:28But the result is so cool because, once again, it spits in the face of

1:31:34these, like, kind of reflexive assumptions.

1:31:39For instance, you could imagine, and I probably grew up hearing, like, oh, you know,

1:31:43he was raised around a lot of girls or something, you know, had a lot

1:31:47of sisters, or he had an older sister or three, right?

1:31:50Or dad left the house, you know.

1:31:52I mean, this didn't happen so much in the 70s and 80s, but it was

1:31:55more frequent in the 90s, you know, back then it was called broken homes.

1:31:59Now people would be like, what are you talking about?

1:32:00Like, everyone knows somebody divorced, right?

1:32:03So, but back then it was more rare, and there was this idea, like, lack

1:32:05of male influence. And, of course, there are important, I believe, gender -specific influences on

1:32:12kids in terms of upbringing, but in terms of the stereotype that seems to have

1:32:18largely dissipated, but that, you know, like having an older sister or three would make

1:32:22a son more likely be gay.

1:32:23It's exactly the opposite when you look at the biology.

1:32:25Yeah, I mean, Ray's looked at that very carefully.

1:32:28And so older sisters don't matter, and neither do younger sisters.

1:32:33And here's the other thing, younger brothers don't matter, right?

1:32:37So no matter how many younger brothers you have, that doesn't change your odds of

1:32:41being gay when you grow up.

1:32:42So it's, that's why I say it's got to be the mother's body that is

1:32:46remembering. And it... It doesn't seem to be socially mediated.

1:32:49It is, you know, independent of that.

1:32:51It is nature having its say.

1:32:55Males with congenital adrenal hyperplasia.

1:32:58We didn't talk about that.

1:33:00And perhaps more important is to talk about males and females with congenital adrenal hyperplasia

1:33:05but are heterozygous. So they have one functional copy, one non -functional copy.

1:33:10And the reason I raise this is that it's very common.

1:33:13It's one in 12. Huh.

1:33:15One in 12. Which seems like an outrageously high number.

1:33:20But it's one of the things that is immediately screened for.

1:33:23Maybe not as much as some other, you know, blood -related diseases and things like

1:33:27that. No, I didn't know that.

1:33:29But I can see. I mean, you have to remember, actually, there are several different

1:33:34genetic mutations along the pathway of making adrenal steroids that can go wrong.

1:33:40And so there are several steps that have to be there for them to make

1:33:44adrenal steroids. So, number one, there's more than one site where the mutations would be

1:33:48carried. And, of course, the heterozygotes may have no symptoms whatsoever.

1:33:54And so they may reproduce just fine.

1:33:56We know this, that, sorry, I should be clear because people are probably thinking, wow,

1:34:00one in 12. Both males and females that carry one mutant copy of CAH are

1:34:05capable of healthy reproduction. There are some hypomorphic phenotypes.

1:34:13Some people make more androgens.

1:34:14Some people have a sustained stress response.

1:34:16It's not very well studied, but it is very common, which I found interesting.

1:34:21Another reason why the carriers are so common is because typically there's no phenotype.

1:34:26Or if there is, it's subtle and so it doesn't come to the attention of

1:34:29any physicians. It's only when two defective copies of the gene come together in one

1:34:36offspring that there's no adrenal steroid production at all.

1:34:39And then things happen enough to get the attention of the doctors.

1:34:42Yeah, I've looked into this and it does seem like one mutant copy of CAH

1:34:46is you find it just statistically more frequent in professions or sports where there's a

1:34:54requirement for long -duration stress tolerance, which makes sense, right?

1:35:01I mean, so some of these genes could confer an advantage.

1:35:03Some could confer a disadvantage in different settings.

1:35:07And that there might be a heterozygote advantage.

1:35:09I mean, you know, the classic example of sickle cell anemia, right, where being a

1:35:14heterozygote for that gene confers an advantage.

1:35:18If there's malaria in the area, you'll be less likely to succumb.

1:35:22Things go wrong when two copies come together in one individual, and that's when the

1:35:27blood cells are especially affected.

1:35:30And things go wrong when an offspring gets two such copies, which is relatively rare,

1:35:35but it does happen. And in that case, then the offspring is very sick.

1:35:40Did you ever do the head transplantation experiment on the finches?

1:35:44That's amazing what sort of a memory you have.

1:35:47No, no, I never did.

1:35:48You want to explain what this was?

1:35:50Because I'm not going to do it correctly, but I remember you wanted to do

1:35:53an experiment where you were going to transplant finch heads.

1:35:57And I thought it was the coolest experiment ever because it was going to be

1:36:00done as embryos. So no, it was not taking heads off of birds.

1:36:05It was an embryo experiment.

1:36:07But I think we should talk about the backdrop of this.

1:36:11Male birds of certain species sing.

1:36:14Female birds don't. Right. So you wanted to embryonically put a female head on a

1:36:20male body, a male finch head on a female body, and you wanted to swap

1:36:26head bodies of these embryos.

1:36:29Tell us the experiment, Mark.

1:36:31I mean, I'm certainly looking like the mad scientist.

1:36:33Well, let me tell you.

1:36:34Wait, wait, wait. Hold on.

1:36:35What crazier things have been done with U .S.

1:36:38tax dollars, like brain bow mice, mice that glow, you know, 215 different fluorescent colors

1:36:45to identify different cell types.

1:36:46I mean, I could go on and on and on.

1:36:48I think this experiment has a purpose to get out a principle that can't be

1:36:55understood any other way. So it's not just tinkering for the sake of tinkering.

1:36:59In fact, people do those sorts of transplants in birds.

1:37:02So a very famous neuroscientist from France, Nicole Le Duran, did these experiments where she

1:37:07would open up chick embryos and quail embryos, and she could scoop out part of

1:37:15the nervous system from one and implant it in the other.

1:37:18And she'd know when she had done it right that she had a way of

1:37:21telling the cells apart under a microscope.

1:37:25Plus, when they grew up, here you'd have this white leghorn chicken with a streak

1:37:29of brown feathers right where she had gone.

1:37:32It's called a quicken. Sorry, couldn't help myself.

1:37:35Here you'd have this white leghorn chicken with a streak of brown feathers in the

1:37:39middle that were derived from the quail.

1:37:41And so it is possible to do those sorts of swaps.

1:37:45And, of course, this is what's so great about working with birds is their embryos

1:37:48are, you know, easy to get to for the first 21 days or so.

1:37:52So people had done those sorts of experiments.

1:37:55There was a question about sexual differentiation of the brain in birds because the –

1:38:02and I'll tell you why it turned out I didn't need to do that experiment

1:38:05and it wouldn't have shown what we wanted.

1:38:10That is – so there are sometimes – You don't have to do this or

1:38:14you don't know how to leverage the fact that you don't have to do that.

1:38:14Thank you. You'll see in the news, someone will find a genandromorph in birds, yep.

1:38:19Genandromorph. Genandromorph, so half female, gen, and half male, andro, and when it happens in

1:38:26cardinals, for example, it's like the animal's been split down the middle.

1:38:30No. Yes, where the one side is the bright red of a male with a

1:38:36crest, et cetera, and the other side isn't, right?

1:38:39So these occur occasionally, and our best understanding of what happened there, first of all,

1:38:44the sex chromosome is a little different in birds than mammals, I'm going to gloss

1:38:48over that, but our best understanding of what happened there is this is a case

1:38:52where two embryos, one that was carrying male sex chromosomes and the other female sex

1:38:57chromosomes, came together at an early stage, and so what we have is a mosaic

1:39:03animal, where one side is genetically male, and the other side is genetically female.

1:39:09Now, in a mammal, if that happened, the testis on the male side would masculinize

1:39:16everything by using hormones. The clue that something else is going on in birds is

1:39:24that in this case, there's not been this blending.

1:39:29And when Art Arnold and others looked at the brains of genandromorphs, sure enough, the

1:39:37sex differences where this region, HVC, for example, tends to be larger in males and

1:39:44females, in these animals, it was larger on one side of the body than on

1:39:47the other. So they were indeed, you know, split.

1:39:51Well, this suggested that gonadal hormones were not in charge of sexual differentiation.

1:39:57And so what I wanted to do, and never figured out quite how to do,

1:40:04was to take a male brain and put it on a female body and vice

1:40:10versa, to ask what sexual differentiation will be like.

1:40:14Will the whole body listen to the brain and become male, or will the gonads?

1:40:21It was a crazy experiment where if I could dissociate what the sex of the

1:40:25gonad was from what the sex of the brain was and what would happen.

1:40:29But it turned out, you know, I didn't have the good hands that you would

1:40:34do, for example. I never learned how to do that experiment.

1:40:37But one resolution of it is, one of the things we now know is going

1:40:40on in birds, is that in some cases, it's the brain itself that's making the

1:40:45hormone and is masculinizing itself.

1:40:48So in birds, there's pretty good evidence that brain sexual differentiation happens because the genetic

1:40:54sex of the brain determines how much hormone, including testosterone and estrogen, is getting made

1:41:01locally, and that that then is driving sexual differentiation.

1:41:05And that's why you can have, you know, one side of the brain is male

1:41:08and the other side is females.

1:41:10And that just doesn't happen in mammals.

1:41:12That's the mechanism, once you start using gonadal hormones to direct sexual differentiation, you can't

1:41:19end up with that sort of mosaicism, which is maybe too bad.

1:41:24I mean, there are carnival acts where supposedly one side of the body is male

1:41:27and the other side is female, and those have been around for quite a while,

1:41:30but that's a different thing.

1:41:32I'm going to give you two real world examples.

1:41:35Real because I was told them, and I believe them.

1:41:40In anticipation of our conversation today, I ventured into some corners of the internet.

1:41:47I kind of wish I hadn't.

1:41:49But, you know, in gym culture, bodybuilding culture, there is a subset of people, I

1:41:58don't recommend it, that take synthetic androgens, anabolic steroids of different kinds and in different

1:42:02combinations. And again, I don't recommend people do this, but it's entirely different than hormone

1:42:10replacement therapy or something like that.

1:42:12Like experimentation with high dosages of different types of testosterone derivatives.

1:42:17And my interest in understanding a little bit of what some of the general observations

1:42:21are there is a naturally occurring experiment with some thematic averages, which is geek speak

1:42:27for like if one person reports something, it means nothing.

1:42:30But if hundreds of people or thousands of people validate that experience, you think, well,

1:42:34it's kind of, you know, these aren't controlled studies, but nonetheless might be interesting.

1:42:39And those communities have long talked about how different forms of androgens have different effects

1:42:47on psychology. And in particular, these days, you can find a lot of discussion in

1:42:53those communities of certain anabolic steroids, a Trenbolone in particular that causes aggression, but that

1:43:00is well known for causing otherwise self -reporting as heterosexual males to start wanting to

1:43:10have sex essentially with males or females.

1:43:13This is an effect that seems reversible when they stop.

1:43:16I mean, it seems generally associated with a kind of a hypersexuality.

1:43:20Yeah. Um, so that's an important variable, right?

1:43:24Um, so there's all sorts of variables there.

1:43:26So, so that's one observation that, um, that makes me wonder if the adult brain

1:43:32is still plastic at the level of the hypothalamus to androgens later in life.

1:43:38Now, this is not to say that the many now millions of men who are

1:43:41taking testosterone over the hypothalamus to androgens after watching the earth.

1:43:42replacement, which is very, very common, doing that safely with doctors' support, et cetera, they're

1:43:48not trying to boost things into super physiological range.

1:43:51But it's a naturally occurring experiment with very few controls and only anecdotal reports.

1:43:58But it suggests that the adult hypothalamus is still androgen sensitive in ways that can

1:44:05drive pretty powerful changes in behavior and perception.

1:44:10And we know that is true because back in the previous century, Julian Davidson at

1:44:16Stanford, actually, in the physiology department there, was among the first to do these double

1:44:22-blind placebo -controlled studies in men who had lost their testes for one reason or

1:44:27another, accident or cancer, things like that.

1:44:30And so double -blind means neither the man nor the physician who was interacting with

1:44:38him had any idea whether he was getting the placebo or the testosterone.

1:44:43And that's, of course, really important for coming up with conclusions.

1:44:47And they concluded that, in fact, the men who were getting testosterone definitely reported feeling

1:44:55better, feeling more energetic, having a higher libido, and they definitely felt better overall.

1:45:01And Julian said, sort of the joke is that even though men were supposed to

1:45:08be blind to which treatment they were getting, they always knew.

1:45:11They always knew when they were getting the testosterone because they felt so much better.

1:45:15So we know for certain that testosterone does have effects on the adult brain in

1:45:21many of these cases, right?

1:45:22These are men's prostate cancer cases who were elderly yet, and still, they still responded

1:45:30to that. Yeah. One thing I learned from your textbook was that, you know, this

1:45:36idea that testosterone diminishes with age is largely true, but the rates are highly variable.

1:45:43And that, you know, there are some individual points on the scatter plot whereby you'll

1:45:48see somebody in their 70s or 80s whose testosterone is very similar to someone in

1:45:52their 20s or 30s. Now, everyone nowadays talks about how testosterone rates are dropping.

1:45:56So it's a, you know, it's, these are older studies, but it suggests that there's

1:46:01a tremendous amount of variation.

1:46:03We also know that absolute numbers don't necessarily dictate how people feel.

1:46:09In fact, the CEO of a very, very, very successful company, not a tech company,

1:46:14an entertainment company came up to me once at a private party and said that

1:46:18his testosterone was down in the low 300s.

1:46:21So this is approaching the lower end of the reference range, but he feels great.

1:46:24And I said, if you're willing, like, what variables are we talking about here?

1:46:27And he explained, you know, vigor and he explained, you know, libido and he explained,

1:46:32you know, general enthusiasm for life.

1:46:34And I said, well, I wouldn't change a thing in that case, right?

1:46:38I mean, there's, he's a perfect case whereby low end of normal is not a

1:46:43problem. And who knows, maybe had he taken more, he would have aromatized more to

1:46:47estrogen and he wouldn't have felt as good for instance.

1:46:50No, no, I agree. I mean, if it ain't broke, you know, leave it alone.

1:46:52Yeah. I think it's something that doesn't get mentioned enough.

1:46:54And, but you also point out why humans are such lousy research subjects, because there's

1:46:59so much variability going on.

1:47:02So what I can say is that for the decline in testosterone levels in men,

1:47:08first of all, it's so much more gradual compared to what happens to women at

1:47:13menopause, right? There's no comparison whatsoever.

1:47:16And there is an incredible amount of variation across subjects.

1:47:19And so once again, even though you can say, statistically, we know this is a

1:47:24trend. I can't make, you tell me someone's 71 years old just to pick on

1:47:30me. I can't predict what their testosterone levels are going to be like or not

1:47:33very well. Another sociological observation from the internet.

1:47:38Everything on the internet is true.

1:47:40Certainly not everything on the internet is sarcastic.

1:47:41I know you were being sarcastic and certainly not everything on the internet is informative,

1:47:45but clusters and averages are interesting to me.

1:47:49There's a meme, which I find interesting vis -a -vis this type of conversation, whereby

1:47:56I think it was a martial artist, a MMA guy from either Russia or some

1:48:05Eastern country, excuse me. The meme is, it goes something like, send two, three years

1:48:12Dagestan and forget. A guy is talking about how he wants his kid to be

1:48:15good at wrestling. And so he's going to send them to Dagestan where apparently the

1:48:18training is very intense. And the meme goes, send two, three years Dagestan and forget.

1:48:22And he said, I'm going to send him there for a few weeks.

1:48:24And then, and the guy goes, no, no, no.

1:48:26Send two, three years Dagestan and forget.

1:48:28And that meme, which is, it's not a cartoon.

1:48:31It's a guy actually speaking in that context, has been, you can find extensive compilations

1:48:38of people showing kind of effeminate boys, dancing, doing kind of theater type activities.

1:48:46And then, then, then it transitions to send two, three years Dagestan and forget.

1:48:50The idea being, returning to the beginning of our conversation, that, that there may be

1:48:54more plasticity early in life and that masculinization of behaviors, stereotypically defined.

1:49:01Okay. I want to be very clear.

1:49:03The idea being that that's very plastic early in life.

1:49:07Okay. I think this is.

1:49:10It's interesting and important to observe because when I was a kid, my mom, she

1:49:19still tells me this story, but she's told me this, verified this for many years.

1:49:22We had a pediatrician. This was in Northern California.

1:49:26This is just a mile or two away from Stanford School of Medicine.

1:49:30And my pediatrician said to her, you have a boy, Andrew, and there are three

1:49:38very important things in raising him.

1:49:41And these were his words.

1:49:43One, don't let him ride motorcycles.

1:49:46I agree. Two, don't let him drink soda, too much sugar.

1:49:51Okay, fair. And he said, three, don't let him do theater.

1:49:57The implication being that boys who do theater have a higher probability of becoming gay.

1:50:03Now, that was – I was born in 1975.

1:50:06Okay. He gave this advice to every parent of a male.

1:50:12And I say that to kind of frame people's understanding of where we were versus

1:50:18where we are. And yet this meme is, I wouldn't say rampant on the internet,

1:50:23but has a fair amount of support for it in the sense that I think

1:50:27there's still the general belief that certain activities can bias sexual orientation.

1:50:32And I just want to zoom out and ask, acknowledge the idea that the brain

1:50:39is plastic to androgens. Behaviors impact androgens.

1:50:42So not trying to corral you into a given answer, but I think we've come

1:50:47a certain distance in this, but we haven't really come that far.

1:50:52Well, and of course, there's no doubt that the younger brain is more plastic.

1:50:56I mean, there's no way around that.

1:50:58But, you know, in terms of what one can do, there are limits.

1:51:03And in terms of sexual orientation, I can tell you people look really hard for

1:51:09any social correlates. You know, you talked earlier about the dad that's missing or even

1:51:15Freud talked about the overly coddling mother and the dismissive father.

1:51:22That might make a boy more likely to be gay.

1:51:25And so people have looked for those sorts of correlates.

1:51:27The data just aren't there.

1:51:28I mean, it's really, which I think is interesting and kind of strange because you'd

1:51:34think that if the social influence was that good, that you'd find something.

1:51:41And so in terms of sexual orientation, I think the data are pretty weak.

1:51:46However, in terms of other expressions of male -like behavior, clearly culture and family has

1:51:54a say, right? I mean, they clearly make an influence.

1:51:57I mean, in terms of what boys are supposed to do, I would say probably

1:52:00the only sex difference that will persist and that almost certainly is due to biological

1:52:06factors like testosterone is, you mentioned already, rough and tumble play.

1:52:11Across so many species, you know, you put a bunch of males together and there'll

1:52:16be a lot more physical activity than if you put a bunch of females together.

1:52:20And an interesting thing happens if you put it in a mixed group and it

1:52:24doesn't matter whether it's monkeys or rats.

1:52:27The overall play will be intermediate.

1:52:30It's like the girls calm the boys down and the boys ramp the girls up

1:52:34a little bit. And so that might be, you know, one that's going to be

1:52:41pretty hard to corral with social influences.

1:52:43But virtually every other expression of masculine behavior, of course, you know, culture and family

1:52:49make a difference. I don't know if, you know, I'm going to suggest anyone send

1:52:54their child to... Dagestan, two, three years.

1:52:57Yes, thank you. Thank you for saying it.

1:53:00The original statement, it was a real statement in a discussion, was aimed at something

1:53:03else. Yeah. It's been co -opted for this, like this is the form of, you

1:53:08know, intervention or whatever you want to call it.

1:53:13Okay. Let's set the internet aside and let's talk about a different upbringing for a

1:53:17moment, which is yours. Oh.

1:53:19As a scientist, you have a somewhat unusual trajectory in the science.

1:53:26So where were you born?

1:53:28In the Ozarks, in Springfield, Missouri.

1:53:31Oh, I was about to say, where are the Ozarks?

1:53:33I know where they are, but to orient our international audience.

1:53:36Southern Missouri and Northern Arkansas.

1:53:38So it's famous because it's hill country.

1:53:41And so very hilly, very much like the Appalachians, both in terrain and in culture,

1:53:48actually. So now I was born in the Ozarks in a working class family.

1:53:52No one in my family had ever, well, no one in my mother's generation had

1:53:57finished high school, much less college.

1:54:00And, you know, I was always a little bit different because I was so much

1:54:08more interested in reading than, all my cousins say, all they remember about me when

1:54:13we were growing up is I always had my nose in a book, right?

1:54:15That, that, that phrase. So, and I, as I get, and I, I, I didn't

1:54:21choose that. I didn't choose to like reading, but I always did.

1:54:25And I always loved school.

1:54:28And so, and, and I will say I had a great family that was incredibly

1:54:34supportive of me doing whatever I wanted to, right?

1:54:36That, that would, that would be fine.

1:54:37That, that would be fine.

1:54:38And as I look back, I realize, and I predict you'll find this too, the

1:54:44older I get, the more I realize how much luck matters and how many very

1:54:51fortunate things happen to me, right?

1:54:53So the first question is, I end up going to Yale College.

1:54:58What? Working class? Working class.

1:55:04So my folks were blue collar workers.

1:55:07I mean, for complicated reasons, I was raised by my grandparents.

1:55:10He was a construction worker and she worked in a food processing plant.

1:55:14And so they once told me that maybe altogether they went to third grade, right?

1:55:20They got that far. But they were clearly smart and great people and they were

1:55:25very supportive. And so here's where, here's an incredibly lucky episode that happened to me.

1:55:33So when I was a junior in high school, I go to the Central High

1:55:37School Library and I volunteered there after work to put away books.

1:55:42And the librarian tells me, oh, there's this book you might be interested in.

1:55:45And she shows me this really thick paperback made out by the college board.

1:55:51So this was the first year that the college board had put together this book

1:55:54showing all the colleges in the United States with little burbs about them.

1:56:00And she said, you might want to look at that.

1:56:03And I opened it up and I see that for all the colleges, there's a

1:56:06paragraph about financial aid. So I read that entire book from front to back, except

1:56:12I only read the financial aid part, because at the time my grandfather passed away.

1:56:17And so my grandmother and I, our only income was Social Security, right?

1:56:20That was, that was, that was our livelihood.

1:56:23And, and, and so I read financial aid, everyone, and I get to the end,

1:56:29they're in this first edition, they were in alphabetical order, which makes no sense.

1:56:34But that's how it was, I get to the end.

1:56:36And the one for Yale College, it's like one of the shortest listings there.

1:56:40And it says, basically, we're committed to making sure everyone admitted will get the financial

1:56:45aid they need. This is me.

1:56:48This is what, this is where I need to read the whole book just to

1:56:50get there. Well, I, the next entry was Yeshiva, which I thought, well, that's a

1:56:53strange name. But if they'd had that paragraph, I believe me, I would have been

1:56:57applying there, which would have been fun too.

1:56:59And so, so I go to my counselor and I say, well, I'd never heard

1:57:04of Yale. I mean, I associate it with locks, right?

1:57:06I'd heard of Harvard because of Kennedy, but, you know, nobody in my family talked.

1:57:10I go to my counselor, her name is Jean Walker, and, and, and she says,

1:57:15that's an Ivy League school.

1:57:18Huh? What does that mean?

1:57:19And she, she, she tells me.

1:57:21And to her credit, she doesn't say, that's stupid.

1:57:23You're never, you know, why, why, why would you be doing that?

1:57:26She says, you know what?

1:57:27You should apply for early admissions this year.

1:57:31Early admission? I know. Okay.

1:57:32So I apply for early admission.

1:57:33I don't get it. So it's okay.

1:57:34But I'll try again next year because that paragraph, it's really got it under my

1:57:38skin. And this is what I need.

1:57:39So apply the next year.

1:57:41And this time they asked me for an interview.

1:57:46And I'm, I'm, I'm to, I'm to have an interview with Dr.

1:57:49John Ferguson. I'm to call up his office and arrange for an interview.

1:57:53And I'm sitting in French class with my friend Dale, and I'm telling him I'm

1:57:58supposed to make an appointment with Dr.

1:58:00John Ferguson. And the French teacher, who was one of my letter writers, Mrs.

1:58:04Fisher, she overhears this. And she says, what on earth?

1:58:07Why would you go see John, Dr.

1:58:10John Ferguson? Because she knew, but I didn't.

1:58:12He was an OBGYN. And I, you know, sort of sotto voce.

1:58:17Well, you know, oh, well, I know John.

1:58:21He's an old family friend.

1:58:22And I used to babysit him.

1:58:24And, you know, oh, well, I'll be calling him.

1:58:26So I'm sure, I don't remember the interview with the man, right?

1:58:30I mean, I don't remember a thing about, but I'm sure he told them I

1:58:33was, you know, the greatest thing on earth.

1:58:35Because I'm sure he gave me as strong a recommendation as he possibly could.

1:58:39And so I got in.

1:58:44And they were true to their word.

1:58:46They sent me this thick letter with all this financial aid.

1:58:51And so, and they didn't expect my family to contribute anything, right?

1:58:56So it was, it worked out.

1:58:58And, you know, and what happened, I have mixed feelings about Yale because I benefited

1:59:05so much. I mean, and I'll credit myself with this.

1:59:09I went with the right attitude, right?

1:59:11Which is, they've made a mistake.

1:59:14Mrs. Fisher got me in.

1:59:15And I'm not going to screw this up.

1:59:18And indeed, you know, I, you know, Andy, I want to know everything.

1:59:23I want to know about art and literature and all the sciences.

1:59:26It was, I mean, I was hungry.

1:59:29And I, so, and I went with the attitude is, man, all these people are

1:59:33smarter than I am. And so I'm just going to soak it up.

1:59:37And at least half of what I learned at Yale, I learned from other students,

1:59:41right? And the first night I'm on campus, you can, you can see what happened.

1:59:46So first of all, I drive from Springfield to New Haven.

1:59:51It's a long drive, but, you know, that's how we go places.

1:59:53We drive. I get to New Haven.

1:59:55It's, where am I going to park this car?

1:59:57I can't, I just thought, of course, there'd be, you know, parking lots.

2:00:01Yeah, and so I find a place in downtown, a garage.

2:00:05And, you know, some of the things we can do to shove.

2:00:05So thank you. Oh, my God, this is going to cost me so much money

2:00:07to keep the car here.

2:00:08I've got to take it back as soon as I can.

2:00:11And I go up to my dorm room in the old campus and I meet

2:00:14my three roommates. And I know how to be sociable, so where did you go

2:00:19to high school? And two of them tell me they went to prep school.

2:00:23Huh? What's a prep school?

2:00:25They explain that to me.

2:00:26And then they start talking about Phillips -Andover versus Phillips -Exeter.

2:00:30And the third guy, I won't mention the name, but his last name is one

2:00:35of generational wealth that every American has heard, right?

2:00:38So it's like, okay, I'm not in the Ozarks anymore.

2:00:42And then they start, you know, smoking dope.

2:00:47And I've never seen that before, right?

2:00:49I've never been around people smoking marijuana before.

2:00:52And they assure me, oh, the campus cops, they'll look the other way.

2:00:56And I'm thinking, well, and that very summer in Greene County, where I'm from, a

2:01:02judge had sentenced a young man for possession of marijuana, had given him a life

2:01:06sentence. Whoa. For possession of weed?

2:01:09This is 1972, and this is the Ozarks, right?

2:01:12Not the same sort of place.

2:01:14So I'm thinking, well, maybe the campus cops would overlook you smoking dope, but I'm

2:01:19not going to give Yale any excuse to send me home.

2:01:21It was like a kid in a candy shop.

2:01:24And because I regarded everyone there as, they certainly knew more than I did, all

2:01:30of them. And they were probably smarter than I did.

2:01:33It was like, I never felt the pressure to be the smartest person in the

2:01:37room, right? Okay, I'm not, I don't care.

2:01:40And I took as many classes as I could.

2:01:44And, you know, I always wanted to take six, you were supposed to take no

2:01:49more than five courses per term.

2:01:52And so I would always want to take six, and the dean wouldn't let me.

2:01:55So I'd take five courses in a lab, which is like half a course, et

2:01:59cetera. And I'm just, you know, I'm not getting nays and everything, but I don't

2:02:03care, right? I didn't, so I'm having a great time.

2:02:07And that's when I learned about neuroscience.

2:02:09So first, someone told me, oh, look at this course about comparative psychology.

2:02:15What's comparative psychology? It means comparing across species.

2:02:19And, oh, I didn't know psychologists studied animal behavior.

2:02:22And then pretty soon, I took a class.

2:02:26Linda Uphouse taught a physiological psychologist taught neuroscience.

2:02:30And I'm hooked, right? I mean, this is, I love this stuff.

2:02:34I mean, it's been an amazing arc to go from the Ozarks to Yale.

2:02:40I love that when you found yourself in an environment that offered a lot of

2:02:43opportunity, that you seized that opportunity.

2:02:46I think many people wouldn't have done the same had they not had your background,

2:02:53but maybe even if they had.

2:02:54I mean, I think that when you find yourself in a place where there's tons

2:02:58to learn and you throw yourself into that, only good things can come of that.

2:03:03I mean, you mentioned luck, but I think, you know, luck is, I wouldn't say

2:03:08evenly distributed, but it has a habit of finding the prepared, as they say, right?

2:03:15I obviously didn't make that statement.

2:03:16Right, right. And I love this theme of exploration.

2:03:19I mean, we, you know, I think of you as the hormones and sex behavior,

2:03:25hormones and sexual orientation scientist, right?

2:03:30But I also remember, you know, it was 25 years ago that you always walked

2:03:36very quickly and you always had an idea that you were excited about whenever I'd

2:03:40run into you. So I want to say you've really inspired my career to go

2:03:45after things that interested me and just really follow those trails.

2:03:49And also when, when it wasn't so clear what to do to pick the thing

2:03:55that at least was most exciting then and not worry about where that was going

2:03:59to lead next. You strike me as one of the least careerist people I've ever

2:04:02met. Like, and I also acknowledge you've had a spectacular career and it's still going.

2:04:09I mean, your name is synonymous with hormones and behavior and hormones and sex behavior.

2:04:12You're being humble now, but it's, it's absolutely true.

2:04:15It didn't hurt that your last name was Breedlove, if I'm honest, but let's face

2:04:19it, that wasn't going to confer you like a real lasting advantage.

2:04:24So clearly you've put in the work.

2:04:26I also really want to thank you for coming here today and teaching people what's

2:04:30known about these topics. And these are not easy topics to parse.

2:04:34The languaging has to be very specific.

2:04:38The reason it has to be specific is in one part political sort of, but

2:04:42it's really about making sure that people understand what's true, what's not true and what's

2:04:48not known yet so that they can form their own ideas.

2:04:52And, and I really admire the way that you're able to do that.

2:04:54And I also learned a ton today.

2:04:56So, you know, I'm struck by a number of different things in this model of

2:05:01how we become who we are.

2:05:02And as someone who's raised kids successfully and, um, and I was grandkids.

2:05:08Yes, I knew your kids.

2:05:09So that's a trip to me.

2:05:10I haven't seen them in years, but they have kids.

2:05:13I think, um, maybe you would just comment briefly on, you know, did you observe

2:05:18early sex differences in terms of behavior?

2:05:20Did it, was it striking?

2:05:22Did you do experiments on your kids or did you opt not to?

2:05:25It was pretty amazing, really.

2:05:27Now that you mention it, because, um, Steve Glickman once told me that there was.

2:05:33Someone did a study where you ask people, how much do you attribute personality to

2:05:37nature and how much to nurture?

2:05:40And he said the only correlation that came out of it was the more kids

2:05:44people had, the more they thought nature was important for determining.

2:05:50And you know that because if you have more than one kid, they're not the

2:05:55same. And so in terms of sex differences, I'll tell you.

2:06:00So I have one daughter, Tessa, and she had two older brothers, et cetera.

2:06:05And you know, my partner, Cindy Jordan, neuroscientist too, and she almost never wore dresses,

2:06:15right? That would be our skirt that was just, you know, not useful around the

2:06:19lab. And there was a period there where every day with Tessa, it was a

2:06:25struggle if we didn't put her in a dress, right?

2:06:27She really wanted to wear – and as soon as she could walk, one of

2:06:32the things she liked to do was to put on her mother's various shoes, right?

2:06:37And walk around in them, cute, et cetera.

2:06:40I mean she was so different from the beginning.

2:06:43Now, I'm not a biological determinist.

2:06:47I don't think – and I don't think biology is everything.

2:06:50I don't think, you know, prenatal things are everything.

2:06:52There's no one cause of any human behavior, but it really struck me.

2:06:57Oh, and one of my boys could make a gun out of anything, right?

2:07:03You know, this is an era where we're trying not to – Even growing up

2:07:06in Berkeley. Oh, my – well, especially in Berkeley because he wasn't going to find

2:07:09a toy gun, but by golly, he could make one.

2:07:12And he was also the kid that, you know, loved any toy with wheels on

2:07:18it, right? So it was – and you know, even among monkeys, right?

2:07:22Melissa Hines showed it first.

2:07:25Even among monkeys, if you put in wheeled toys, it's the male monkeys that are

2:07:29much more interested in that than the females.

2:07:31And the female monkeys are much more interested in the dolls, et cetera.

2:07:35So, yeah, you have more than one kid.

2:07:38I predict you're going to be amazed about how, you know, how different the kids

2:07:43are, even though you're the same family, right?

2:07:47They don't all come out the same.

2:07:49Once again, you've been a huge inspiration to me over the years.

2:07:52And I know that the listeners are greatly appreciative of everything you've taught.

2:07:56And we've got to get you back here.

2:07:58Oh, also, you're writing a book about the biology of sexual orientation.

2:08:01I didn't know this. We don't do – we actually don't really do book promos.

2:08:05That's not really our podcast.

2:08:06But when can we expect that book to hit the shelves?

2:08:09Oh, you put me in such a tough spot.

2:08:12So I'm struggling with it.

2:08:14I've written six chapters and I'm intending to be 11.

2:08:18My goal is can I get this first draft done by this fall?

2:08:22And then, you know, there's reviewing and things like that that will happen.

2:08:25So I do – you know, knock on wood.

2:08:27I'm really hoping I'm going to finish this book.

2:08:30And if so, well, you know, I expect you – since you owe me so

2:08:34much, I expect you to buy a copy.

2:08:36Absolutely. I'll buy a copy.

2:08:37I'll read it and I'll let the world know what I think about it.

2:08:40Dr. Mark Breedlove, thanks for coming here today.

2:08:43Come back again. It was a pleasure.

2:08:44I've had a great time.

2:08:45Thank you. Thank you for joining me for today's discussion with Dr.

2:08:49Mark Breedlove. To learn more about his work, please see the links in the show

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2:09:28For those of you that haven't heard, I have a new book coming out.

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How Hormones Shape Sexual Orientation & Behavior | Dr. Marc Breedlove