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Dr. Marc Breedlove on Huberman Lab: How hormones shape sex

Why otoacoustic emissions at birth differ by orientation, and how the 2D:4D digit ratio tracks prenatal testosterone without predicting any individual.

Andrew HubermanhostDr. Marc Breedloveguest
Mar 30, 20262h 11mWatch on YouTube ↗

EVERY SPOKEN WORD

  1. 0:00 – 3:24

    Marc Breedlove

    1. AH

      The larger the number of older brothers that a male has, the higher the probability that he is gay.

    2. MB

      It's been seen over and over. I mean, it's, it's really one of the, uh, rock solid findings in human sexuality. So the way to emphasize the difference is, uh, if a baby boy is born today, um, if, if he has no older brothers, his odds of being gay when he grows up is about two percent, right? Pretty low. But if he had one older brother, his odds go up by a third. Okay, two point six. And if he has two older brothers, they go up a third again. All right, now we're at three point... It, it turns out you gotta have, like, a, a dozen older brothers just to have a fifty-fifty chance. [instrumental music]

    3. AH

      Welcome to the Huberman Lab Podcast, where we discuss science and science-based tools for everyday life. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. My guest today is Dr. Marc Breedlove. Dr. Marc Breedlove is a professor of neuroscience at Michigan State University, and he is an expert in how hormones shape the developing brain, in particular how they influence sexual orientation. As you'll learn today, the amount of testosterone that a fetus is exposed to while in the mother has a profound impact not only on the ratio of finger lengths, yes, you heard that right, but it also plays a meaningful role in sexual orientation, and in fact, there's a correlation there between finger length ratios and sexual orientation. Now, as wild as that may seem, that result has now been confirmed many times over in humans and in animals, and today you'll understand why. You'll also learn that every time a woman is pregnant with a male, there's a biological trace of that which biases the likelihood that her next male offspring will be either heterosexual or homosexual. Now, I know this sounds really out there, but these are extremely solid biological findings for which the mechanisms are now understood for both animals and humans. It turns out that the hormones we are exposed to while we are in the womb shape not only the preference for whether somebody's attracted to males or females, but also an aversion to the opposite, meaning there appears to be the formation of circuits for being attracted to one sex and not attracted to the other. Today you'll also learn how hormones impact the amount of rough-and-tumble or social play that kids engage in, the interplay between nature and nurture in shaping male versus female differences, and sexual orientation. Dr. Breedlove is one of the longstanding pioneers in this field of how hormones shape brain development and psychology. We approach these questions through the lens of biology and statistics, so today's is not a political discussion. Instead, it's a discussion about what is known and what is still not known about this profound aspect of our species. Oh, and we also talk about gay rams. Yes, that's a real thing, and it has important implications for everything we've mentioned thus far. By the end of today's episode, you'll surely think differently about the relationship between hormones and brain development, nature and nurture, and romantic partner choice. Before we begin, I'd like to emphasize that this podcast is separate from my teaching and research roles at Stanford. It is, however, part of my desire and effort to bring zero cost to consumer information about science and science-related tools to the general public. In keeping with that theme, today's episode does include sponsors. And now for my discussion with Dr. Marc Breedlove.

  2. 3:24 – 7:37

    Hormones & Sexual Orientation

    1. AH

      Dr. Marc Breedlove, welcome.

    2. MB

      Thank you. I'm delighted to be here. Very exciting.

    3. AH

      Been twenty-five years since we stood in the same physical space.

    4. MB

      I know. How can that, how can that be possible when I f- I feel like, you know, just saw you a few days ago, but then-

    5. AH

      Well, you look great.

    6. MB

      Thank you.

    7. AH

      Uh, you look the same, so [laughs] uh, we can talk longevity protocols at the end, but-

    8. MB

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

    9. AH

      Well, um, I've wanted to have you on this podcast since I launched it because you work on one of the most interesting things in the world, which is how and why people become who they are and how hormones play a role there, how genes play a role there. If you're willing, I'd like to jump from the high dive to the deep end-

    10. MB

      Okay

    11. AH

      ... first. Right off.

    12. MB

      All right.

    13. AH

      Let's talk about this finger length ratios sexual orientation study that-

    14. MB

      Sure

    15. AH

      ... you published, and somehow I landed on that paper.

    16. MB

      [laughs]

    17. AH

      That's not why I wanna talk about it. I wanna talk about it because it's an incredibly interesting set of findings. Other people have done the same-ish experiments, and there's a whole context there about how hormones influence sexual orientation independent of behavior.

    18. MB

      We need to step back a little bit for the context of one thing that your listeners might not know is, you know, in the year two thousand there was still a lot of people who regarded, um, s- same-sex o- orientation as a choice, a lifestyle choice. That was the, the political c- combination of words that meant you could disapprove of people, um, because they were attracted to the same sex. Of course, I'm, I'm at Berkeley. I, I didn't have any truck with such notions at all, and, and, and I've always been convinced that sexual orientation is not a choice, and there's a exercise I do in class where I ask... So I'm gonna put you to it. Now, so remember the first time you had a crush, right?

    19. AH

      Mm-hmm.

    20. MB

      It might've been someone on TV, might've been someone at a playground, et cetera. So think about it, and I, I want you to tell me about how old you were at the time in a moment. My guess is it was before puberty.

    21. AH

      Yeah, I was six.

    22. MB

      Yeah.

    23. AH

      So-

    24. MB

      Same here

    25. AH

      ... and I hit puberty somewhere starting around fourteen.

    26. MB

      So, so it had nothing to do with puberty, right?

    27. AH

      Mm-hmm.

    28. MB

      It was this thing that happened, and, and I'll, I'll share my experience. So, so I'm about six or seven. I couldn't have been more than seven, uh, and Marilyn Monroe is on TV. I'm dating myself. And there's a close-up, you know, with that face and the, and the mole, et cetera, and afterwards I'm just so agitated. I don't, you know, I don't, I, um, and I know nothing about sex. I remember I had a hard time going to sleep, so it's, it was like something about this was really agitating me, and I didn't choose to have that reaction.And my guess is that whatever sex you had your first crush on, that's the one you're gonna be attracted to the rest of your life.

    29. AH

      Yeah, it's been constant.

    30. MB

      So, yeah. Well, so, so, so this idea that it was a choice, that always just seemed so absurd to me. On the other hand, um, even though, you know, I'd, I'd been doing animal research with giving hormones early in life and seeing what it did to the nervous system, et cetera, um, and every time I wrote an NIH grant, I said, "Well, you know, the effect of early hormones may be important for human behavior," but to tell you the truth, I never actually believed that, right? It was just, I, I just wanted to justify it. Be- because it seemed to me that we are so sensitive to social influences, and we have this long stretch of time where we're, you know, our brains are still growing at a fetal rate of growth until at like nine or 10 years of age, and we're taking in so much information. And, and think of what a, what a heterosexual world is, right? I mean, all those Disney movies with Prince Charming and et cetera. Uh, and so it always seemed to me that, that social learning would be more than enough to explain why ninety-five percent of people are straight. But that doesn't mean it was a choice, and it doesn't mean that they would even be aware of what the social influence was. So, so my example is I speak English. It's, you know, I'm hopelessly monolingual, only language I speak. Well, I don't remember learning English, and I certainly didn't choose to learn English, but I'm sure that it's English because of social influences, right? So

  3. 7:37 – 14:08

    Prenatal Testosterone, Finger Ratio, Men & Women Differences

    1. MB

      that was where I stood on the question of sexual orientation until nineteen ninety-eight, nineteen ninety-nine when this fellow at University of Texas, Dennis McFadden, came out with a paper where it really made me think that prenatal testosterone might have an effect after all, despite my expectations. And this was looking at otoacoustic emissions. Do you wanna, wanna talk about those?

    2. AH

      Yeah. These are, uh, people's ears making noise.

    3. MB

      Yeah. I mean, right now, as in, in, in this studio, if, if I, if I shut up for a moment, your ears will continue to make little popping sounds that you're not aware of because having grown up with it, the, the brain stopped you from perce- perceiving those long ago. Well, but if Dennis puts you in a soundproof room and puts a very sensitive microphone in your ear, he'll, he'll hear these pops. And, uh, and I, I won't get into the acoustics of why that's a good thing, right? It helps you to focus on the sounds you wanna hear. But what Dennis knew is there's a sex difference in how many of these otoacoustic emissions are being made. Girls make more, and it's present at birth. So Dennis comes out with a strange study, I mean, who would do such a thing, where he, he proposes, well, since the sex difference is present at birth, it might reflect prenatal testosterone, and so he measured the otoacoustic emissions in straight men and gay men and straight women and lesbians. And he reports that, that the, compared to straight women, the lesbians have fewer of these otoacoustic emissions than straight women. It's like, well, what? [chuckles] What, how would that happen? Um, how... I, I, I couldn't think of any way to explain that except that, well, well, the lesbians might have been exposed to more prenatal testosterone than straight women before birth. And I don't know how to explain that except to say, well, maybe prenatal testosterone, maybe if you're exposed to that before birth, you're more likely to be attracted to women when you grow up. Which, oh, well, that might explain why n- ninety-five percent of men are attracted to women, right? 'Cause they're all exposed to prenatal testosterone. So this oddball study really gets me to thinking that maybe there's, you know, something to that. But, but I forget it. You know, I'm, I'm still working with my rats and, and Peromyscus and Siberian hamsters and stuff. I'm happily doing that. And then [chuckles] I, and I remember it so well, and I, I, in nineteen ninety-nine, I'm in, in my office at Berkeley, and I read this paper that says there's a sex difference in the, the ratio of fingers that's present in nine-year-old children. What? I've studied sex differences my whole adult life. How do I not know about this? And, and it turns out that, that if you, if you measure the length of the second digit-

    4. AH

      The, the pointer finger

    5. MB

      ... the index finger, the pointer finger.

    6. AH

      For those just listening, yeah.

    7. MB

      Right. And the, the length of the ring finger, and you can, you can do a simple ratio. Divide the length of the second digit by the fourth digit, so-called 2D:4D ratio, and a guy named John Manning was reporting that there's a sex difference there, that it's, th- that that ratio tends to be smaller in men than in women, and that it's present in children. It's like, well, wait a minute, a sex difference in the body that's present before puberty, I know enough about sexual differentiation of the body. It, it's almost certainly due to prenatal testosterone.

    8. AH

      Forgive me for interrupting you, but people-

    9. MB

      Yeah

    10. AH

      ... are probably looking at their hands right now.

    11. MB

      Oh, yes. Yeah.

    12. AH

      And, um, I just wanna point out that these are averages.

    13. MB

      Yes.

    14. AH

      But it's, I think the 2D:4D thing, for people that aren't familiar, even though you explained it quite clearly, can be a little confusing. Basically, in men, the finger lengths are more different than they are in women, and there are some differences-

    15. MB

      Sure

    16. AH

      ... in s- uh, in that statement according to sexual orientation that we'll get into.

    17. MB

      Right.

    18. AH

      But when you say, uh, the d- the, in other words, the typical heterosexual male pattern is that the pointer finger-

    19. MB

      Right. Mm-hmm

    20. AH

      ... is shorter than the ring finger.

    21. MB

      Right. Right.

    22. AH

      Whereas in women, they tend to be more similar.

    23. MB

      That's right.

    24. AH

      Again, these are averages. And not to give it away, but this is, because people are looking at their fingers right now-

    25. MB

      Yes. Yeah, yeah

    26. AH

      ... um, that, uh-

    27. MB

      Let, let, let me just say, don't panic.

    28. AH

      Yeah. Right.

    29. MB

      We're gonna, we're gonna walk you through this.

    30. AH

      Right.

  4. 14:08 – 16:46

    Sponsors: David & Rorra

    1. AH

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  5. 16:46 – 23:57

    Finger Ratios, Prenatal Testosterone, Gay & Straight Men/Women

    1. AH

      Well, as long as we're getting into the context, it's interesting 'cause you said there, there are a lot of, uh, gay people in the Bay Area. But it was very clear, as I recall when doing the study, that if we wanted to get a, a large sample population of, uh, gay men, we would need to go to the Castro District in San Francisco.

    2. MB

      Yeah, as we did. Yeah.

    3. AH

      And if we need to get a large cohort of gay women, we need to go to the Solano Street Fair in Berkeley. [chuckles]

    4. MB

      Well, and, and in Oakland. So there, there, there was a, there was a brand new, uh, Oakland, uh, gay festival that got started. And yeah, there, uh, Oakland is a wonderful place to find lesbians. So, um, one of the, one of the charms of the place. I thought the whole idea was kind of crazy, actually. I mean, I didn't think we'd come up with anything. And I insisted on measuring all the, all the digits myself, right? Which I did twice. Boring as hell.

    5. AH

      I recall when we were on, what was it, like, third floor of Tolman Hall-

    6. MB

      Mm-hmm

    7. AH

      ... uh, and you came running in.

    8. MB

      [laughs]

    9. AH

      I was talking to my advisor-

    10. MB

      Yeah, yeah

    11. AH

      ... our good friend Irv Zucker-

    12. MB

      Yep

    13. AH

      ... one of the pioneers of circadian biology, discovered the suprachiasmatic nucleus-

    14. MB

      Absolutely

    15. AH

      ... with Bob Moore and others. But, um, and you came running in with, [chuckles] with, with a ruler, and you said, "Give me your hands."

    16. MB

      [laughs]

    17. AH

      And you grabbed my hands, and you measured them, and you go, "Well, that's weird 'cause it's, like, different on one hand than the other." And then you go, "Okay." And you took the notes, and you measured his hands, and you left. And I thought, "What in the world is he doing?"

    18. MB

      [laughs]

    19. AH

      It turns out that was the early origins of the study.

    20. MB

      Yeah. Yeah. No, no, a-and, uh, anyway, so, so I, I measure these hands and, um, and I'm doing the, the, the math at the end of the day, and lo and behold, I mean, I don't, I don't see any difference in the digit ratios of gay and straight men. Right? Okay.

    21. AH

      Between gay and straight men.

    22. MB

      Yeah. Yeah, I didn't see any difference there.

    23. AH

      Which itself is interesting-

    24. MB

      Absolutely

    25. AH

      ... 'cause it impliesMore or less equivalent amounts of prenatal testosterone exposure

    26. MB

      Which I think is the case, yes.

    27. AH

      Mm-hmm. And, and right now, just forgive me, but, um, you know, might, some people might say, "Well, that's not surprising." But in the '80s and '90s, the Hollywood stereotype of gay men was that they were all very effeminate.

    28. MB

      Yep.

    29. AH

      Um-

    30. MB

      Yep

  6. 23:57 – 26:54

    Mice & Sex Differences, Androgens

    1. MB

      blast.

    2. AH

      I mean, when some of the more outrageous things that people have asked me about this study over the years, uh, were, and by the way, they all came from men-

    3. MB

      [laughs] Yeah

    4. AH

      ... uh, were, "If I cut off my, uh, index finger, um, you know, will that raise my testosterone?" Someone actually asked that.

    5. MB

      Yep. Um-

    6. AH

      No, it's not reverse causality.

    7. MB

      I would've said, "Well, let's try it and see." [laughing]

    8. AH

      Again, now most people, I realize there are differences across the country and the world o- on this stance, but I think most people would say, "Yeah, like, okay, there's a biological variable, um, associated with sexual orientation." The fact that it's linked to prenatal testosterone is very interesting. Um-And the question that then comes up is, is there anything about behaviors associated with gay or straight men, gay or straight women, that change hormone levels independent of all this, right? 'Cause, um, put differently, I think for a number of years, people were interested in whether or not gay men, as you pointed out, um, would have higher or lower levels of testosterone. The, the hypothesis was lower based on the effeminate stereotype. Turned out probably the opposite outcome.

    9. MB

      If, if, if anything, right.

    10. AH

      Yeah.

    11. MB

      Right.

    12. AH

      Anyone that went to gyms in the 1980s and '90s, uh, would, would also realize that the, uh, the low androgen argument was wrong.

    13. MB

      Yeah.

    14. AH

      Although steroids become a problem in gyms too. But, you know, it gets confounded. But am I correct in remembering that this effect is also present in frogs or mice?

    15. MB

      The sex difference is present in mice, yes.

    16. AH

      That's D2, D4 ratio difference.

    17. MB

      The... Yes. I mean-

    18. AH

      I find that amazing.

    19. MB

      Well, I, I did too. Uh, so, so, so, uh, Wendy Brown and I did that first. And, you know, I'd worked with mice and rats all my life, but, you know, I'd never noticed that, that, that, that their, this is their, the, that the first digit is their shortest, and that the third digit is the longest, and that sometimes [chuckles] the second digit is longer than... I, I, you know, it's like, I mean, it's, you know, evolution's real, right? That it happened. Uh, and so yeah, there's a sex difference there, and a group looked at mice and did lots of genetic manipulations, and it turns out that if you, if you make the androgen receptor dysfunctional, the sex difference goes away. And they showed that in mice at least, there's more androgen receptor in the, the growing bones of the fourth digit than the second digit, and then they showed that, um, that that's why the fourth digit grows a little bit more than the second digit.

    20. AH

      Beautiful. So the ma- And, uh, we, I should have said this earlier, androgens are things like testosterone-

    21. MB

      Exactly

    22. AH

      ... um, DHT, other, other androgens.

    23. MB

      Right.

    24. AH

      Um, men and women both have them, uh, other animals have them. Um, incredible. So let's talk about effects of testosterone when we're in the womb.

    25. MB

      Yeah.

    26. AH

      Obviously, it's having an organizing effect on the body plan, this D4 to D2 ratio.

    27. MB

      Right.

  7. 26:54 – 33:52

    Brain Differences & Sexual Orientation

    1. AH

      What about in the brain? What is known about brain differences between men and women that identify as straight or, um, gay?

    2. MB

      Well, i- in, in terms of prenatally, we don't know, but, but the very famous study from Simon LeVay, who's already a highly respected neuroscientist, lots of wonderful papers in development of the visual system, um, S- Simon LeVay got everyone's attention well before we did when he looked at a brain region in the hypothalamus, a specific region called the preoptic area, or POA, and he looked there and compared, uh, the, the size of the POA in the brains of gay men versus straight men. And he looked in the preoptic area because in rats there's a very prominent sexual difference or sex dimorphism in a nucleus in, in the rat brain in the preoptic area, and the, the nucleus got named the sexually dimorphic nucleus of the preoptic area, the SDNPOA. And Simon knew there was a huge sex difference there in rats, and so he looked at the brains of gay and straight men and found a nucleus there that may or may not be the same as the SDNPOA, but is larger in men than in women, and what he found was that the, the nucleus in gay men was smaller than in straight men, and in fact, not significantly different from the size of the nucleus in women.

    3. AH

      So it wasn't hyper male like the finger-length ratio was.

    4. MB

      No. No.

    5. AH

      Okay.

    6. MB

      No. The, in that case, it indicated less, either less androgen exposure or less of a response to the androgen that was there. And, uh, Simon got even more of an uproar than I did, uh, published his paper in Science, and, uh, there were lots of people that were very skeptical, including some neuroscientists, but, but eventually another group replicated it, you know.

    7. AH

      That's what I was gonna ask, because I recall that the two major critiques of the paper, um, one was fair in my opinion. It was that some of the postmortem samples were from people who had died of AIDS, and so AIDS has some known neurodegenerative effects-

    8. MB

      Yep

    9. AH

      ... that may or may not have impacted the samples, although hopefully they controlled for that. And then as I recall, he also got some pushback because he is openly gay, and people accused him of gen, uh, agended, I didn't say gendered, I said agended-

    10. MB

      Yep

    11. AH

      ... science.

    12. MB

      Yep. Yeah, that-

    13. AH

      You know

    14. MB

      ... that, that, that he was part of some conspiracy, right, a gay agenda to, to, to force Americans to regard people with same-sex orientation as somehow okay. Mm-hmm.

    15. AH

      But a replication of the study from an independent group that presumably has no reason to be biased whatsoever-

    16. MB

      Well, they, they were very skeptical of it, so that was William Byer, who, uh, eventually... It, it, and, uh, there's an interesting aspect of it. It took him a long time to get a sample big enough because, you know, Simon, it was such a horrible time in AIDS epidemic. There were so many young men dying, um, that, uh, Simon had no trouble finding enough brains to do the sample, and, and then as treatment got better, the, the death rates of HIV started going down, uh, and so it took longer for William Byer to gather the samples. But, but eventually he did, and, and even though he was skeptical of it, he saw it too. The, the A- the, the question about AIDS, I mean, Simon was able to address that in that, um, he also had some straight men who had AIDS, and, and he didn't, you know, they didn't, they weren't significantly different from other straight men. Um, but, but a- and so it was widely interpreted as proof that sexual orientation is not a choice, that it's something that happens to youAnd of course, I don't think sexual orientation is a choice. That's true. But Simon himself made it clear that he could only look at this nucleus in adults, right? You can only look... It's so tiny. The sexually dimorphic nucleus, the preoptic area in humans, it's, it's about the size of a grain of sand, right? So you gotta have a microscope, and you can only-- there, there's no non-invasive way to look at it. And he pointed out that he didn't know if what, what the order of causation was. He didn't know if those men had been born with a smaller SDNPOA, and that's why they became gay, or did something else cause them to become gay and also cause the SDNPOA to get smaller. And for, for the public, the idea that a nucleus might change its size in adulthood, maybe that seems kind of like, you know, unlikely. But as neuroscientists, we know, you know, that adult brains ch- are changing all the time. Uh, in, in fact, e-even in animals, Brad Cook showed that, you know, there's a nucleus, the medial amygdala, um, uh, there's sex difference there, but if you take away the testosterone in males, sex difference goes away in just a matter of a few weeks. So Simon's work, uh, on the SDNPOA, also known as INA3, I won't bother with why the- that abbreviation-

    17. AH

      Unfortunately, I remember the full name [laughing] because my brain-

    18. MB

      I know. You-- Yeah.

    19. AH

      It's the interstitial nucleus of the anterior hypothalamus-

    20. MB

      Absolutely. Yeah

    21. AH

      ... subregion three. I'm not saying that to impress anyone. When you get to be fifty, which I can now say that, you wonder why your hippocampus remembers certain things that are, like, basically totally useless to remember.

    22. MB

      I, I waste so many synapses on, on totally useless crap. [laughs] But, uh, but that's not, that's, that's, that's worth holding on to. You did well. So, um, but, uh, so, so we don't know, uh, it's a chicken and egg problem. We don't know if, um, if that happened, um, if, if they were gay because they had a small INA3, or do they have a small INA3 because they're gay. So what, what I liked about Dennis' otoacoustic emissions and it is pretty good evidence that that happened well before they, they had a sexual orientation. And, and the other thing I always liked about it is that, well, well, I, I mean, you can't imagine there's a social influence on, on digit... And, and be-- and nobody, nobody knew about this. So I wasn't worried that there were some little girls out there that looked at their hand and say, "Hmm, gee, that looks kinda masculine. Maybe I should be a lesbian," right? Because nobody knew this.

    23. AH

      Until your paper was published.

    24. MB

      [chuckles] Yes. Yeah.

    25. AH

      I mean, as I recall, there wa- there was some, like, schoolyard stuff of kids looking at each other's hands-

    26. MB

      Absolutely

    27. AH

      ... and trying to decide who was gay and who was straight, and-

    28. MB

      You know what? Every once in a while, to this day, on, on the internet, I'll look at a... and there'll be a little ad over there of the... claiming to, to tell me something about my personality based on the, on, on, on digit ratio length, and it's just like, you know, please, uh, yeah, there's nothing to it. Don't waste your money, gang. And there's an aspect to this, this, this fact that, that the group differences were there, but you can't tell about differences between individuals, that, that I think is the hardest thing for scientists to communicate to the public at large.

    29. AH

      Yeah.

  8. 33:52 – 36:57

    Group vs Individual Differences, Height Analogy; Bisexuality

    1. AH

      You, you have a really good way of explaining this to people because... And it's an important lesson just in reading statistics and, and making sense of data that, um, I'd love for you to give an example of-

    2. MB

      Sure

    3. AH

      ... how this plays out perhaps in a separate example.

    4. MB

      Psychologists, uh, they like to talk about h- a way of measuring how big a difference is between two groups. So this difference in digit ratios between men and women, it's, it's a relatively small difference. It's like, well, we measure it in terms of how many standard deviations apart are the two means of the populations.

    5. AH

      The two averages.

    6. MB

      The two averages. And, uh, to give an example of that, everyone knows about the sex difference in human height, right, a-among adults. So that's a huge sex difference. It's one where we're all aware of it, and if, if nobody had told us it was such a thing, we'd notice it after a while, right? And that, that's because those two averages and those two populations are about two standard deviations apart. The standard deviation being a measure of how much variability there is in something. So that's a huge sex difference. And to give you an idea of what that means, if I had you grab a, a, a sample of a thousand people, and I'm gonna tell you one thing about each one of them, and that's their height. That's all. And now I give you the job. You've gotta guess what sex they are, and I can tell you what you wanna do to, to maximize your hit rate. Everyone who is five feet, five and a half, you're gonna say those are men. And if they're less than that, you're gonna say they're women. And you'll be right about eighty percent of the time, which means you'll be wrong almost twenty percent of the time, right? And so everyone, you, you can, you can see that, that there's some predictive power there, but n-not-- it's far from perfect. Well, this sex difference in digit ratios is half a standard deviation, so a quarter of that. And so th-that means there's much more overlap. And that, and, and we know that other things influence digit ratios too, not just prenatal testosterone. And so, uh, this is why there's no predictive value. I mean, so anyone who looked at their hand while we were talking about this and got worried, um, I don't know anything about your particular prenatal testosterone level no matter what your digit ratio is.

    7. AH

      What about bisexuality? People who identify as attracted to both men and women, and maybe we ask about first bisexual women, then bisexual men. Is there a pattern in digit ratios that leads anywhere?

    8. MB

      I mean, in those days, we didn't have enough people that identified as bisexual to, to have a reasonable sample. And it's interesting, and that, and that's something that's changed, right? I mean, if you do surveys now, especially for among younger people, there are more people who report that they are bisexual than there were then. So, so I don't really have anything to say about them. The one thing I will say is I'm sure that even among lesbians, there's more than onepathway, more than one developmental pathway to, to, to become a lesbian or to become a gay man, right? I, I don't think there's just one thing. That's not how human behavior-

  9. 36:57 – 42:52

    Brain Development, Hormones & Behavior; Brain Plasticity

    1. AH

      But you do think it's, based on the data, that it's biological.

    2. MB

      Based on that data, I think testosterone has a say.

    3. AH

      Mm-hmm.

    4. MB

      Right? That it... N-now, doesn't, doesn't mean it's the whole package.

    5. AH

      Prenatal testosterone.

    6. MB

      Prenatal testosterone.

    7. AH

      And the reason I ask that is, I mean, there are conditions that are not uncommon where, um, someone has a particularly stressful, long phase of development where there's every reason to believe that their androgens are impacted negatively.

    8. MB

      Yes.

    9. AH

      There's also every reason to believe that there are stretches of development where androgens are increased. Like, we know that people who do a sort of a, a contact sport-

    10. MB

      Right

    11. AH

      ... um, or engage in anything that requires s- like, deliberate aggression. I realize that real martial artists-

    12. MB

      Competitiveness

    13. AH

      ... know, competitive aggression, know how to, you know, sort of, um, gate their levels of aggression so that they're not, they're not, like, in, in a fury, right?

    14. MB

      Yeah.

    15. AH

      Um, like it... But we know that certain types of activities, competition, et cetera, I mean, there's no question that those can increase androgen. So the... You can imagine there's some plasticity postnatally.

    16. MB

      Of course.

    17. AH

      And that could be before puberty. It could be during puberty. And, and so that's testosterone. There, the body, as you, you said, you said something that even as a developmental neurobiologist [chuckles] I don't think I'd ever, um, heard, uh, stated so clearly, and it's so important, that, that the rate of brain development from birth until age 12 is at least as fast as it was before we're born.

    18. MB

      Yeah, the, I mean, the, the way to really bring that home is to compare human brain growth and chimpanzee brain growth. So up until birth, the rate at which the brain size increases compared to body size is about the same in humans and chimps. And shortly after birth, the chimpanzee brain stops growing as fast and eventually asymptotes right away. The human brain continues that feverish fetal rate of growth until at least six years of age, maybe out there to 10 years of age.

    19. AH

      Mm.

    20. MB

      So, uh, people have pointed out that in, in a real sense, human beings, children are fetuses that are outside learning a whole bunch of stuff from other people. That's the real distinctiveness of our species is, you know, we have this protracted childhood and really intense social learning, and as you say, a fetal rate of growth even though we're not in the fetus anymore.

    21. AH

      So I guess for me, the, the idea that behavior, exposure to things, uh, you know, and I don't wanna get into valence of negative, positive, but sure, pesticides, but also, uh, you know, a-schoolyard activities.

    22. MB

      Yeah, yep.

    23. AH

      If you have, and we'll get to this, you know, uh, five siblings, and it's very competitive of who gets how much pizza.

    24. MB

      [laughs]

    25. AH

      I've been, you know... I had one sibling, so it was a little bit, you know, there was competition-

    26. MB

      Yeah, yeah

    27. AH

      ... but it was different, right?

    28. MB

      Yeah.

    29. AH

      You know, it, it, these things change hormones. Hormones change the brain. The brain, as you're explaining, can impact sexual preference.

    30. MB

      What's great about studying hormones and behavior, right, is, is that sometimes you can control the hormone in animals at least. But the hard thing about hormones and behavior that people don't understand is that behavior can affect hormones, as you say. In, in competitions, the winners afterwards are more likely to have higher testosterone, and the losers will have lower. In elections, it's been shown that people whose candidate won the presidential election, they, their testosterone levels went up a little bit, and the people whose, whose candidate lost went down a little. And so you'll always have this cycle where the, the hormone alters the behavior, and then the behavior alters the hormone, and, and you always have to look for ways to try to pin down, uh, the order of, of, of effects, um, and you know, not always easy. The only thing I know for sure is, is that the brain remains plastic all of our lives.

  10. 42:52 – 44:16

    Sponsor: AG1

    1. AH

      As many of you know, I've been taking AG1 for nearly fifteen years now. I discovered it way back in two thousand and twelve, long before I ever had a podcast, and I've been taking it every day since. The reason I started taking it and the reason I still take it is because AG1 is, to my knowledge, the highest quality and most comprehensive of the foundational nutritional supplements on the market. It combines vitamins, minerals, prebiotics, probiotics, and adaptogens into a single scoop that's easy to drink, and it tastes great. It's designed to support things like gut health, immune health, and overall energy. And it does so by helping to fill any gaps you might have in your daily nutrition. Now, of course, everyone should strive to eat nutritious whole foods. I certainly do that every day. But I'm often asked, "If you could take just one supplement, what would that supplement be?" And my answer is always AG1 because it has just been oh-so-critical to supporting all aspects of my physical health, mental health, and performance. I know this from my own experience with AG1, and I continually hear this from other people who use AG1 daily. If you would like to try AG1, you can go to drinkag1.com/huberman to get a special offer. For a limited time, AG1 is giving away six free travel packs of AG1 and a bottle of vitamin D3K2 with your subscription. Again, that's drinkag1 with the numeral one .com/huberman to get six free travel packs and a bottle of vitamin D3K2 with your subscription.

  11. 44:16 – 51:37

    Sexual Behavior, Libido

    1. AH

      What are some of the other effects in human studies of behavior impacting hormones that come to mind for you? I mean, it's been a while since we've touched into this, and we haven't done it much on this podcast. I mean, obviously competition, winners, losers, you explained the data there. Um, what are some other scenarios? Just studies that, that have been striking to you or that have stood out over the years.

    2. MB

      No, I, I think for testosterone, I think the big ones have been, have, have been competition, you know, between males. Um, and no, I don't, you know-- I mean, there, there's a stress response, but that's a whole other thing. Um-

    3. AH

      What about sex behavior itself?

    4. MB

      In animals at least, we know that, that there's a relationship there, that, that in, in males, in males of most species, let's take rats, uh, if you take away the testosterone, within a few weeks, they'll, they'll stop mounting altogether. And if you give them testosterone, after a few weeks, they, they start mounting again, right? So we know that that, um, plasticity is, is there, and we know that it's driven by testosterone. But, uh, in, in animals where they're in charge of their own testosterone, we've known for a long time that if a male is exposed to the odors of a receptive female, that causes a spike in their testosterone. And so, uh, that's kind of preparing them for maybe, maybe some- maybe I'll be lucky. Maybe there's something coming down the pike. Uh, and so we know that that's a reciprocal relationship, uh, when the animal's in charge of the, of the hormone.

    5. AH

      For the longest time, thanks to your textbooks-- And by the way, folks, uh, Marc has, um, authored some of the most important textbooks on hormones and behavior, developmental neurobiology. I mean, he's a, he's a true scholar of the whole field, and so I'm immensely grateful to him that those textbooks have formed the backbone of a lot of, uh, solo episodes of the podcast.

    6. MB

      Yeah.

    7. AH

      So, um, you know, the textbook version of male versus female sexual behavior has been a story about females having a circuit that goes from brain to body to control this thing they call lordosis, the arching of the lower back, the receptivity, the willingness to mate, and the males having a circuit that goes from brain to spinal cord to body, um, involving, uh, arousal, erection, mounting, um, insertion, ejaculation. I mean, your lab and others has really parsed this, uh, right down to the, the details. And yet, of course, people have sex that way, but also other ways. And so for a lot of people who aren't familiar with hormones and neural circuits and behavior, the sort of strict context kind of is, is-- still forms the framework, you know. I mean, I, I've learned, uh, and I'm now fortunate that this podcast has been around more than five years, so I no longer have to tap dance around things, right? So people will say, "Oh, well, you know, there's this lordosis behavior in the female. She's, she's receptive, um, or not. Um, he mounts," etc. And then there's gay men who have to have sex a certain way that mimics the female sex pattern of behavior. And so people do this one-to-one, right?

    8. MB

      Yeah.

    9. AH

      And I think that it's understandable why they do that if they're not educated. But how should we make sense of these biological circuits that are in the textbooks that define stereotyped, literally motor behavior? It's almost like saying like, like females have sex this way with males. Males have sex this way with females. But then the caveat is always like, "Oh, but in humans, all that goes away," and there's these like bonobos that are a little bit more like humans. So did we waste all our time-

    10. MB

      [chuckles]

    11. AH

      ...um, studying that stuff? [chuckles] I mean, really.

    12. MB

      And you're getting at exactly what every textbook author has to deal with, right? Which is, you know, uh, as the old joke go, you, you, you, you look where the light is, right?

    13. AH

      Mm-hmm.

    14. MB

      So we know so much more about the circuits f- that are involved in the motor behaviors because they're relatively easy to trace and relatively easy to manipulate and relatively easy to, to study. We know lots about the motor patterns in animals. We know a lot less about the motivational patterns in animals, which in human sexual behavior is-- I mean, in many ways, that's the whole show. You know, that's, that's really what's-- Uh, and, and we don't really have good animal models of, of libido, right? And this was brought home to me s- many years ago now. I, I was on a session of "60 Minutes," the CBS News program, and, uh, Leslie Stahl was there in our lab. I mean, the producers had called me up and said, you know, "Can you show us a way that, that early testosterone exposure changes behavior permanently?"And I said, "Sure, I can do that. Give me some time." So I went to the lab and castrated a bunch of rats on the day of birth. I know how to do that. I'm not proud of it, but I, I know how to do that. Um, and they came three months later, and, uh, so I, I showed them those motor patterns you talk about. So here's a typical female. I've given her hormones, estrogen, progesterone, so I know she's gonna be receptive. And here's a male rat that I know has had lots of experience copulating. And, uh, Leslie immediately dubbed him Romeo. Okay. Well, this is Romeo. And it, she hates rats, by the way, so she, she was, she, she was very brave. And so I, I drop a female on top of Romeo, and he starts mounting, and she shows the lordosis posture, and it's all beautiful and easy. And we do that several... I said, "N-now, I'm, I'm gonna drop a male, a control male in." And Romeo, of course, you know, you don't know unless you try. He mounts several times, and the male rat acts like nothing's going on. I mean, it's just the bored thing on Earth, and Romeo eventually gives up. Now, I drop into the cage a, a male rat who I castrated on the day of birth, ninety days before, and I've given him the same hormones I gave the female to make her receptive. Romeo hops on, and sure enough, a beautiful lordosis, right? The, of the sort that the, that the control male never showed. So here this pre... this, this neonatally castrated male is showing very female-like patterns. And Ms. Stoll kept asking me, "Would you say this is a gay rat?" And it's, you know, I'm sitting there, and I'm, I'm definitely in a tough spot because I don't think my rats have an orientation. I mean, we, we just saw Romeo happily mount any rat I threw in the cage, 'cause y- what do you know? You know, try your luck. Um, and so, uh, you know, uh, she asked me several... And I, I knew she wanted me to say that, but I said, "What I would say..." I don't remember exactly what ended up in the final edit. I mean, what I would say is that th-this is a rat whose sexual behavior has been permanently changed because of something that happened to him a long time ago, at the very beginning of development. And, and really, that's the best I can do in terms of any rat model of sexual orientation. I don't think my rats have a sexual orientation. If I give the female those hormones, she's going to show lordosis to whoever mounts her. And my male rat, he w- he will mount any rat he comes across just in case he gets a lordosis out

  12. 51:37 – 58:00

    Gay Rams, Brain Differences

    1. MB

      of them.

    2. AH

      Well, good on you for not, um, getting, uh, corralled into giving a particular answer. Uh, I've recently joined CBS as a correspondent. If we have this conversation on 60 Minutes, I promise to not, uh-

    3. MB

      [laughs]

    4. AH

      ... try and force an answer. Romeo is an interesting, um, case because I think for most people, including myself, um, I thought that you were gonna say that Romeo was willing to, um, try to mount a female-

    5. MB

      Mm-hmm

    6. AH

      ... if she was receptive, he would mate. If not, he wouldn't. Um, but I was surprised that he would try to mount a male as well. That doesn't align, at least with my experience of, of male human behavior.

    7. MB

      Well, certainly not. That's right. This is the thing that's distinctive about humans is we're not actually that particular about what particular behaviors we engage in, what motor behaviors w- and we're overwhelmingly interested in who our partner is.

    8. AH

      Mm-hmm.

    9. MB

      Right? That is an overriding concern that, that I don't think my rats have. I think, I think few animals do. Here's the... Y- you're the anthropologist from Mars, and, um, and I tell you, "Here's a person that fifty percent... Here's..." Uh, whoever's the Sexiest Man Alive this year, People Magazine, or I don't know who that happens to be.

    10. AH

      Well, this is an interesting discussion altogether 'cause there's this... People have been lining up the images of these people and claiming that there's sort of like this effem- like effeminate drift-

    11. MB

      Ah, interesting

    12. AH

      ... that takes us back to a time in the early nineties when there was this sort of revision about male, male facial structure.

    13. MB

      Fascinating. Yes.

    14. AH

      We can get back to that.

    15. MB

      Yeah, yeah, yeah.

    16. AH

      But yeah.

    17. MB

      Okay. Okay.

    18. AH

      Yeah.

    19. MB

      Well-

    20. AH

      It's not... The, the point being that it's not fixed.

    21. MB

      Who... Yes.

    22. AH

      Yeah.

    23. MB

      Well, well, whoever, l- let's say it's George Clooney. So, uh, so here's someone that half the planet believes is an ideal sexual partner, right? But the other half of the planet finds him totally unacceptable, even if the behaviors they engaged in would be pretty much the same. And so, you know, in, in terms of positions and who's doing what to whose genitalia, et cetera, I mean, for, for, for most people, it, it isn't that there has to be one particular act. I suppose there's some, but, uh, for most people, there, there may be a variety of acts that they, that they want to be engaged in with that other person, and their overwhelming concern is the, the, the gender of that other person or the sex of that other person. Um, you know, it's, it's hard to have an animal model of that. I actually do know one example in sheep, if you wanna talk about this.

    24. AH

      Of all things. [laughs]

    25. MB

      Yes. Oh, I, I, I, I noticed it. So, um, so, uh, uh, Chuck Roselli out at, out at Oregon, he's the one that studied this very carefully. I guess shepherds have known for ages, um, that in any herd, there are some rams who will not mount a female ever and keep mounting other males. And of course, to maintain a shepherd, a, a, to maintain a herd, you don't need every male to reproduce. So, but in the old days, they got, those males got sent off to slaughter, right? They... Well, um, hearing these rumors, uh, Chuck did these tests where he would put a bunch of females that are in stocks, so they can't move, and they're all ready for mating, and he put a ram in with them, and most rams, of course, will mount the females. He, he puts in s- these rams that, that prefer males-If there's a variety of sheep's butts sticking at him, out at him, uh, he'll mount males, including sometimes, you know, having intromission through the anus and all the way to ejaculation. And, and he never mounts a, a female. In some cases, they'll have one of these, I'm gonna call them gay rams. I think, I think they have an orientation. He'll put this gay ram i- where there's a dozen females, and he might be in that paddock for twelve hours and never mount a single female.

    26. AH

      Highly unusual for male rams.

    27. MB

      And these are not typical ram. There's, it's like a small percentage of the population. And, um, and I don't know how to explain that. I mean, you would think that the, that these gay rams, that, well, you know, an ejaculation's an ejaculation, right? An orgasm's an orgasm. I presume they have or... You, you would think that at some point, that, "Well, there's nothing else to do in here. I'll mount one of these ewes," and they never do. And I don't know how you can explain that except that there's some aversive component that, that, that, that rams do care about the sex of their partner-

    28. AH

      Mm-hmm

    29. MB

      ... and that, and that for these gay rams, um, there's some aversive component to that. Um, by the way, Chuck told me, uh, not too long ago, there's a company that has identified these gay rams and decided that instead of sending them off to slaughter, they're gonna harvest their wool and sell them as, a- and, and make them into clothing. So you, you can buy, you can buy, um, wool clothing, uh, that, that came from gay rams and, and know that you saved them from the slaughterhouse.

    30. AH

      There's no response that's appropriate to, to that statement.

  13. 58:00 – 1:06:58

    Aversion Pathway, Men vs Women, Same-Sex Partner

    1. AH

      This is a particularly, um, nice moment, uh, not just for this episode but for the entire podcast arc, uh, because there are these moments that come up every once in a while where a larger principle shows up in a new way that I think, um, is really important for people to understand. Across neuroscience, we see this push-pull, right? A, a flexor muscle like the bicep, when it flexes, the tricep relaxes. Uh, when the tricep flexes, the, the bicep relaxes, these antagonistic relationships. You see this in the hunger circuit. I mentioned one earlier. Like, uh, hunger and feeling full are, they're like a push-pull. They're like a seesaw. And, um, uh, and you see this over and over and over again. It's a, it's a, it's a very consistent theme of, of brain function. And you said something that I was not aware of. It makes perfect sense. I just wasn't aware that there were, you know, data, um, at the level you describe, which is clearly there's an appetitive aspect to sex behavior, heterosexual males wanting to have sex with females, heterosexual females wanting to have sex with males, and, a- and so on, every derivation there. There's a desire. In species where there's strong pheromone and odor determination and, and receptivity stuff, it gets played out that way. It g- looks one way. In humans, it may have some of that, but it plays out different way. Receptivity is communicated differently. Although odor may be very important in ways we don't q- quite fully understand. But this idea that there's an aversive aspect to it, right? I think this is important, and it's something that I have not heard discussed before. And I think that sociologically it has relevance because I think that, um, there's so many different aspects to the notion that our species, humans, um, come in gay and straight and perhaps bisexual varieties. We know that's true.

    2. MB

      Clearly.

    3. AH

      But there is this, um, not uncommon theme whereby s- many people, I, um, I can only, you know, say many people, right, not all, um, that the concept of mating with same sex is aversive to them, and that has shaped a lot of the, the landscape around this. And I'm, I'm not trying to get political here. It's just, I think it's, it's worth acknowledging that that may be a real phenomenon too. I'm not trying to justify mistreatment of anybody, but I think that we're never gonna get where we wanna go as a s- as a species, um, societally until we really at least understand the biology and how to work with it. And so the idea that same-sex sex, right, um, would be aversive a- as an idea to people, some people are like, "Oh, well, they haven't been educated." Okay, perhaps, you know?

    4. MB

      Yeah.

    5. AH

      The, but there may be a biological basis for that.

    6. MB

      I think the data are still out, and I, uh, but I think it's, uh, it, to me at least, it's pretty clear that for men at least, for m- I mean, it, there's an asymmetry here, uh, that, that, that experiment where I said, you know, "Who wants to have sex with George Clooney?" Half the population says, "Sure," the other half of the population n- never. If we reverse the experiment, "What percentage want to have sex with Margot Robbie?" And yeah, half the population, the men would see her as a very desirable sexual, um, partner. But, you know-The women too would, many women would also would at least consider the idea of having sex with her. And, and we know there are plenty of women who are straight in one part of their lives, and later they fall in love with a woman, and now they feel like they're, they're gay, right? So females, women are more plastic in terms of their sexual longings and sexual orientation, uh, than men are. I'll, I'll be a little more specific. I, I think it's among males where sometimes for many males, not all, uh, there's an aversive c- idea. That, that the idea of having sex with the same-sex partner is aversive. Now, o- of course, context matters, right? There's same sex happening in prisons all the time when, you know, if the conditions are, are enough. And, and I don't know where that aversive component came from. It could be that our society, maybe it's all, uh, socially inculcated, you know, again, before we're aware of it at all. Um, but I, I think there's also at least the possibility that there's a biological component to it. And, and I think that's what, uh, Chuck was getting at in that here's this difference in the brain. He, he doesn't know when the difference happened, uh, in the preoptic areas, um, but it seems to correlate with this idea that maybe these gay rams, um, no, they, they, they're not interested in having sex with her. They're, you know, only-

    7. AH

      It's aversive to them.

    8. MB

      It's aversive, yeah. There's no other way to ex... I, I can't, I don't know any other way to explain, uh, how they choose never to, never once mount a female.

    9. AH

      Yeah, I feel like the, the acknowledgement of a, of an a- aversive pathway for sexual partner choice is as important as the acknowledgement of biological, uh, correlates of homosexuality.

    10. MB

      Yeah.

    11. AH

      Because if this sort of conversation is ever to advance past the sort of like, okay, what's okay to say now that we're willing to say now, trust in science disappears. I really believe that. Now, of course, the problem is that people leverage fragments of what they hear in order to make arguments in, in favor of whatever stance they have, and that, that's the complication. That's why I like long form, because no matter what gets pulled out, we can go back to the full conversation.

    12. MB

      Right. And this makes you old-fashioned because this, that's not the world, I mean, our world seems to be hurtling towards this-

    13. AH

      Yeah. Yeah. I mean-

    14. MB

      ... world of snippets

    15. AH

      ... people will notice that we have not used the word gender. We're talking about biological sex and sex the act, and we're talking about male versus female partner choice, and we're talking about a desire for one or the other and an aversion to one or the other, and I think the aversion piece is an important theme. So here's a hypothesis, if I can come do a sabbatical.

    16. MB

      Sure.

    17. AH

      I'm due for a sabbatical at some point. It may be that in male humans, that there's a pathway or a molecule that serves as an aversive to sex with other men circuit, peptides, neurons, et cetera, that suppresses, um, sexual desire and activates some level of disgust. Let me just say it bluntly.

    18. MB

      Okay.

    19. AH

      Might not be the same disgust that they would experience to something more aversive, but okay.

    20. MB

      Right.

    21. AH

      And that in women, there is no such pathway. There's either desire for women or desire for men, but as you said, you know, statist- statistically, women are more open on average to same-sex a- interactions, and it may be because there's no aversive signal or the aversive signal has a less robust circuit.

    22. MB

      To me, that, that would explain these differences, the, these sex differences in who people are willing to have sex with. Your hypothesis fits the data.

    23. AH

      I mean, it is true that in the, like, the early nineties for instance, when the first gay characters were on television, like the real, first Real World, and I'm really dating myself here, and subsequent char- characters started to dismantle some of the stereotypes that had been seen in, like, comedies in the eighties and things like that, of the effeminate gay man.

    24. MB

      Yeah.

    25. AH

      Right? What you saw was indeed that heterosexual women, as far as we know, seemed to be more, like, generally accepting of gay men before heterosexual men embraced that as, as typical.

    26. MB

      That's my impression too.

    27. AH

      Right.

    28. MB

      I think, I think it's pretty clear.

    29. AH

      Yeah. And then, and then there's a societal shift, and then it sort of becomes like, you know, uh, like if you... Like, I spend some time on X, formerly known as Twitter, right? And, and there's some, um, gay political, uh, accounts and, um, and you just kinda notice, like, it's just people are, like, comfortable with it. Men and women seem to be comfortable with that, right?

    30. MB

      Yeah.

  14. 1:06:58 – 1:13:55

    Congenital Adrenal Hyperplasia (CAH), Intersex Phenotypes

    1. AH

      that we haven't talked about, and it is a small percentage of people, but it's something that, um, people think about, um, is this notion of sort of, um, neither here nor there, kinda mixed sex, right? Is there a biological correlate of that? Um, a graduate student my year when you were my professor-

    2. MB

      Yes

    3. AH

      ... um, Nicki Osypka, Nicola Osypka-

    4. MB

      Mm-hmm

    5. AH

      ... um, who was already famous for dog, training dogs for the Beastmaster show-She's amazing. Um, and had very well-behaved dogs, uh, that she would bring everywhere with her. Studied a species of mole in Tilden Park that could transdifferentiate its testes into ovaries and back again. And I thought, "Well, that's like alien, weird levels of stuff." But she would occasionally go over to UCSF when babies were born that were sort of, back then they called them, no one uses this language now, pseudohermaphrodite.

    6. MB

      Ah, yes.

    7. AH

      What is the deal with exposure to prenatal androgens and neither clearly here nor there genitalia?

    8. MB

      Yeah. So in, in most of those cases, we're talking about congenital adrenal hyperplasia, also known as CAH. And the congenital means it's present at birth, and the adrenal hyperplasia is referring to the fact that the adrenal glands are slightly larger. And the reason they're slightly larger in this case is because these are individuals where the, the, the fetus itself is not able to make some of the adrenal steroids that are important for staying healthy. And so the brain detecting, "Hey, where's the, where are the adrenal steroids that we need here?" drives the pituitary to tell the h- the adrenal gland, "Hey, we need more steroids." The adrenal gland gets the message, it hypertrophies, but the machinery isn't there to make those steroids, and so instead, the adrenal gland makes testosterone and other androgens. And actually, this can happen in either XX or XY individuals. And in XY individuals, uh, people might not notice. But in XX individuals, what that means is that prenatally, her genitalia are being exposed to more testosterone than is typical. And so, uh, under the influence of this extra testosterone, the clitoris may grow to be bigger than the typical clitoris. In some cases, in extreme cases, um, the, the phallus looks like a penis, and the skin around that area that would normally form the labia, uh, again, there might be enough testosterone that it starts to look like a scrotum, except of course there are no, there are no testes inside there because this is an XX individual. So these individuals are identified at birth typically, especially in XX, uh, individuals. And there's a, there's an easy treatment, which is, oh, they can't make... You, you know, you do the test and you go, "Oh, they can't make adrenal steroids, so we'll give them some." And so for the rest of their lives, they take adrenal steroids orally and get the benefits of that, and that shuts off the hyperactive adrenal gland, so the, it shuts off the, the role of the output of testosterone. So this is an, what's known as an intersex phenotype. And, uh, yes, you're right. In, in the older literature, they were sometimes known as pseudohermaphrodite. Huh? With the idea being whether a hermaphrodite is some, is an individual that can, that can function and reproduce either as a male or a female. And so supposedly they were pseudo because they can't do that, because they have only ovaries. Well, uh, you can imagine, uh, first of all, um, being called hermaphrodite, nobody liked that. And if you asked them, "Well, is it better if I put this pseudo at the beginning? Does that, that make you feel like you're being less stigmatized?" Uh, no. [chuckles] Uh, but a, a much more accurate, uh, description is to say that it's intersex. They have a, a phallus that's somewhere between a clitoris and a penis, and the skin around there is sorta like a scrotum and sorta like a, a, sorta like labia. So, uh, in the old days, once this got recognized, it was standard procedure to tell the parents, "Oh, uh, this is an emergency. We need to do cosmetic surgery. We need to do surgery to make this little girl look like all the other little girls." You know, sometimes the surgery was, you know, it could sometimes be successful or not. Indeed, they knew how to make her look like o- other girls. Um, but many of those intersex folks, when they grew up, were pretty angry that someone had done this surgery on them that wasn't needed medically, right? They were already taking care of the problem with the exogenous adrenal steroids, and so who asked you to, to deal with my, you know, to do surgery on my clitoris? In some cases, uh, the tip of the clitoris was missing, and so these women grew up and were anorgasmic because they couldn't get the stimulation that they normally would have had. These days, um, there's much more, thanks to the activists like Cheryl Chase and others who s- started getting the pediatrician's attention, "Hey, you, you need to think about that. You're, you're doing s- elective surgery on an infant who cannot possibly have informed consent." And so these days, there's more of a wait and see attitude, which I, which I think is absolutely the... So wait till they're grown up and ask them then if they want to have surgery, and, um, my guess is most will, will, will say no. I, I think that's been the c- pattern so far. So these are females who are exposed to more testosterone than other females, so does that mean that they're going to be attracted to women when they grow up? And, and the answer is, well, interestingly, uh, if you look at groups of women with CAH, they are more likely to be same-sex attracted, to be lesbians-

    9. AH

      Hmm

    10. MB

      ... than the, than the population at large, but most of them are straight. But what's interesting about that is the older they get, as you keep surveying them, the higher the percentage of them r- report having a lesbian orientation.

    11. AH

      Hmm.

    12. MB

      So it's possible, first of all, that indicates that, yeah, maybe prenatal testosterone increases the, the odds of them, uh, being lesbians when they grow up. Uh, and, and you also wonder, well, how many of them always had that same-sex attraction butYou know, were following the pathway society laid out for them, and then as they get older, they say, "Well, no, screw this. I, you know, I, I know who I'm attracted to. I don't have to fit the heterosexual mold." And so it, it's, you know, that's entirely consistent with the idea that prenatal testosterone makes you more likely to be attracted to women when you grow up.

  15. 1:13:55 – 1:18:14

    Androgen Insensitivity Syndrome (AIS)

    1. MB

      There's another syndrome that I know you've talked about, um, which is Androgen Insensitivity Syndrome, sometimes abbreviated AIS. And it turns out the gene for the androgen receptor that responds to testosterone and other androgens is on the X chromosome. And it may sometimes be that a woman will have an X chromosome that has a copy of the androgen receptor gene that doesn't work. And if she passes that X chromosome onto a daughter, uh, then she's sort of duplicated herself. What's interesting is when that X chromosome is given to a son, in other words, that egg with an X chromosome that has a dysfunctional copy of the androgen receptor gene, if it gets fertilized by a Y-bearing sperm, now we have an XY individual, and as you've explained clearly in your, in your Basics podcast, uh, we know what'll happen in development. The Y chromosome will mean that the indifferent gonad will develop as testes. The testes will secrete two hormones that are gonna guide sexual differentiation in the periphery, one of them being anti-Mullerian hormone, which is going to suppress the development of the Mullerian ducts, and therefore no oviduct, no uterus will form. And the testes will also release testosterone, which normally would masculinize the body, but in this case, because there's no functional androgen receptor to respond to it, the testosterone goes round and round, but the body doesn't respond. And so the Wolffian ducts don't develop. The periphery looks like a typical female. And these individuals, when they're born, often are not identified because the baby's born, the doctor does that very careful analysis by looking between the legs and says, "Congratulations, you have a girl." And they, uh, grow up to, to be girls un- undetected. And they come to a doctor's attention when puberty happens and all their classmates are having their period, but she's not. And so she'll eventually go to an OBGYN who will first do a, an exam, a vaginal exam, and he'll notice that the vagina is relatively short because the inner part of the vagina is normally derived from the Mullerian ducts. Well, in this woman, in this teenage girl, um, the Mullerian ducts never developed because of anti-Mullerian hormone, so there'll be no cervix that can be seen in the exam. And if he takes blood plasma levels, he'll see that this very feminine-looking girl, teenage girl, has very high levels of testosterone.

    2. AH

      And presumably testes.

    3. MB

      And if he does a karyotype, he'll see that she has an XY karyotype. And yes, there are testes in there, typically in the abdomen, and they're releasing lots of testosterone because there's no negative feedback to tell the brain, you know, "Hey, you can stop s- sending signals to the testes now." In these cases, you can ask, "Well, what's the sexual orientation of these women?" And the vast majority of them grow up to be straight. They are attracted to men, and they might be very-- They're often very interested in having a family, and of course, they can't carry children themselves, but they can, you know, adopt and things like that. And so they're very much feminine, very straight women.

    4. AH

      But they're XY.

    5. MB

      But they're XYs. So the question is, and unfortunately, in terms of understanding whether prenatal testosterone alters our sexual orientation, these individuals aren't, aren't useful to us because we don't know if they're straight women because their brains could never respond to the prenatal testosterone, or are they straight women because they were raised as girls and socialized to, to be attracted to men? It's a fascinating syndrome, and there's at least one woman with AIS who's self-identified, who's a successful model, uh, and there's another woman who wrote a memoir that's quite, uh, it's, it's, it's quite good. And what's interesting about it, when there's no testosterone response, uh, they have very feminine faces, very feminine bodies, uh, and so they're, you know, they're frankly quite attractive, uh, as women.

  16. 1:18:14 – 1:19:25

    Sponsor: Function

    1. AH

      I'd like to take a quick break and acknowledge our sponsor, Function. Function provides over one hundred and sixty advanced lab tests to give you a clear snapshot of your bodily health. This snapshot gives insights into your heart health, hormone health, autoimmune function, nutrient levels, and much more. They've also recently added access to advanced MRI and CT scans. Function not only provides testing of over a hundred and sixty biomarkers key to your physical and mental health, it also analyzes these results and provides recommendations for improving your health from top doctors. For example, in a recent test with Function, I learned that some of my blood lipids were slightly out of range. As a result, I decided to start supplementing with nattokinase, which can naturally help reduce LDL cholesterol, and it did. In a follow-up test, I could confirm that this strategy worked. My blood lipids are now back where I want them, in range. Comprehensive lab testing of the sort that Function offers is so important for health, and while I've been doing it for years, it's always been overly complicated and expensive. But now with Function, it's extremely easy and affordable. To learn more, visit functionhealth.com/huberman and use the code Huberman for a fifty dollar credit towards your membership.

  17. 1:19:25 – 1:32:55

    Gay Men & Older Brothers, Maternal Immunization Hypothesis

    1. AH

      I'm realizing I, I'm drawing a model over here whereby we've got, again, accelerators and brakes and, and I think we've gotDifferent axes. Um, not, you know, I'm not trying to, um, split hairs here, but I think for people who wanna understand how hormones, sex, and behavior, sexual orientation fit together, it's very useful to think about, okay, you've got chromosomes that drive, you know, our typical notions of male versus female, and you're providing some important caveats where the, the body appears one way, but it's an XY, you know, and, and, and there's almost every derivation of this has been-

    2. MB

      Yes

    3. AH

      ... observed, although not at a very high frequency. Um, and then you've got choice of same versus other, uh, in terms of orientation, and a key role of prenatal testosterone there. Um, maybe some cultural or other types of plasticity that might be biased more toward the female side. It seems that way based on what you're saying, if I'm, you know-

    4. MB

      Yeah

    5. AH

      ... I'm willing to say it if you're not. It does seem that way. Um, there's an aversive signal that kind of, that certainly in male sheep and, um, other species and that, you know, matches my observations, uh, as a 50-year-old male who grew up in Northern California and, you know... I mean, again-

    6. MB

      In this era

    7. AH

      ... and the joke being that I'm, I can only speak from my own reference point on this. Um, and then we have a bunch of different things about, um, partner preference and, and that at some point it almost seems like it departs from... Well, it certainly departs from our sort of linear like, okay, uh, girls like boys, boys like girls, testosterone makes boys, estrogen makes girls. But we're, we're, we're nowhere near there. We're, we're, we've left that station a long time ago.

    8. MB

      Exactly.

    9. AH

      Um, and at the same time, we, we arrive at a place where I think we need better languaging to separate these axes because it is very confusing for people. Um, and so that would be very useful if, if the fields of neuroscience and psychology would start to embrace the real-world, uh, realities of, of... 'Cause I actually think the lack of s- of specificity of talking about orientation versus biological sex and, and these, and these other aspects have, have led-- I think that's the source of a lot of conflict, actually. Anyway, that's a, that's an editorial for another time. Um, in terms of biological impact on sexual orientation, one of the more striking findings that you've been talking about for a number of years that just kind of shocks at first, but then you get a lot of nods from people, is this idea that the larger the number of older brothers that a male has, the higher the probability that he is gay.

    10. MB

      It's been seen over and over. I mean, it's, it's really one of the, uh, rock solid findings in human sexuality that, that was first noticed by Ray Blanchard w- at Toronto and has been seen in many populations all over the world. So the way to emphasize the difference is, uh, if a baby boy is born today, um, if, if he has no older brothers, his odds of being gay when he grows up is about two percent, right? Pretty low. But if he had one older brother, his odds go up by a third. Okay, two point six. And if he has two older brothers, they go up a third again. All right, now we're at three point f... It, it turns out you gotta have like a, a dozen older brothers just to have a fifty-fifty chance from the same mother.

    11. AH

      Right. So we know that it's not, you know, in, you know, what they call now blended family or... So this is-

    12. MB

      We'll get to those in a moment.

    13. AH

      Mm-hmm. Mm-hmm.

    14. MB

      But, but, but this is what you see. So y- you get a big population of men. Here's, here's a big population that have one older brother. How many are gay? And it's a small number. And, and the number that have two, still a small number, but more. And, you know, how do you explain that? Uh, we saw it when, when we did those surveys. We... I, I don't know if you remember, we also asked people how many older brothers and sisters they had and how many younger brothers and sisters they had. So it, it turns out in the general population, there are about 105 boys born for every 100 girls, right? That's also very consistent finding.

    15. AH

      105 boys born for every 100 girls.

    16. MB

      That's right. So there's... But... Or put it another way, uh, if you want, I, I can, I can guess the sex of any baby that's gonna be born, and I can be right more than 50% of the time because I'm always gonna guess boy, right? 'Cause 51% of the time it'll be a boy. For straight men, you total up all the older brothers they have and all the older sisters, and there's a ratio of about 105 older brothers to 100 older sisters. For the gay men, it, it turned out there were 140 older brothers for every 100 sisters. So-

    17. AH

      Help frame that statistic for people. So l- so you gave us the one older brother, what the probability was.

    18. MB

      Right.

    19. AH

      Uh, it's a third increase. You go from 2% to two point six. I- is it a linear increase? As you increase the number of older brothers, do you just start-

    20. MB

      It's, I mean-

    21. AH

      ... um, increasing the probability at every, with every older brother, or are there, is it sort of a step function?

    22. MB

      It is in fact a linear progression, so at, at that rate. So Ray's worked that out. Of course, it's hard to find men that have had more than four or five older brothers, especially these days. But, uh, but it turns out in the Kinsey surveys, Ray went to the Kinsey surveys way back then. You know, those sur- those interviews were incredibly thorough, and so they have a record of how many siblings of each sex every one of those men had, and, and you can see it there too. And it's another one of these cases where I tell you this, and you tell me, "Well, I know somebody who has two older brothers, and they're gay. Is that why?"

    23. AH

      Or I know somebody with three older brothers, and they're not gay. This, I'm just, I-

    24. MB

      Ab- absolu-

    25. AH

      Yeah.

    26. MB

      So you tell me, "Oh, I know someone who has two older brothers, and he's gay. Is that why he's gay?" And I, I really can't tell you. There's no way to know because, in fact, most men with two older brothers are straight.Right. Again, it's one of these instances where it gives you no predictive power about one individual, why they are gay. Ray Blanchard has done the statistics, and their estimate is of all the population of gay men, about one in seven are gay because their mother carried brothers before them. And what I mean is those same men with the same genotype, same genes, if their mom hadn't had older brothers before them, they'd be straight today.

    27. AH

      Statistically speaking.

    28. MB

      Statistically. But I, you know, you, you show me a picture of the, of the gay men's chorus, and I can't point out which, which man is gay because of that, because there are other factors that can influence whether someone grows up to be gay. So again, it's one of these things where the statistical comparison is of great theoretical importance, even though it offers no predictive value for a given individual.

    29. AH

      So we know that males engage in much more rough and tumble play when they're younger, just like rats, just like monkeys. This is a fact. It's related to testosterone exposure. If a boy has older brothers, there's a decent chance he's engaging in more of that than if he has a sister. And given what you said earlier, that in humans, the brain continues to develop at a, at a massively accelerated rate, um, even after birth, up to age six, testosterone has an influence. Behavior impacts testosterone. Okay, they're not in puberty yet, but you could imagine this has an impact. So the que- the experiment becomes for boys that had two or more older brothers but were not raised with those older brothers, does the effect hold of them having a statistically greater probability of being gay?

    30. MB

      It's a beautiful hypothesis, and you first hear about this, and that's the first thing you think. Well, maybe the younger brother got bullied or-

  18. 1:32:55 – 1:35:41

    CAH Carriers, Advantage, Stress Tolerance

    1. AH

      Males with congenital adrenal hyperplasia, we didn't talk about that, um, and perhaps more important is to talk about males and females with congenital adrenal hyperplasia, but are heterozygous. So they have one functional copy, one, um, non-functional copy, and the reason I raise this-

    2. MB

      Yeah

    3. AH

      ... is that it's very common. It's one in 12.

    4. MB

      Huh. I didn't know that.

    5. AH

      One in 12, which is, seems like an outrageously high number, but it's one of the things that is immediately screened for, maybe not as much as some other, you know, blood-related diseases and things like that.

    6. MB

      No, I, I didn't know that, but, but, but, but I can s- I mean, you have to remember, actually there are several different genetic mutations along the pathway of making adrenal steroids that can go wrong, and so there are several steps that have to be there for them to make adrenal steroids. So, so number one, there's more than one site where the mutations would be carried, and of course, um, the heterozygotes are, you know, may have no symptoms whatsoever, and so they, they may reproduce just fine, and-

    7. AH

      We know this, that-

    8. MB

      Yes

    9. AH

      ... that, sorry, I should be clear, 'cause people are probably thinking, "Wow, one in 12." Uh, both males and females that carry one mutant copy of CAH are capable of healthy re- reproduction. Um, there are some hypomorphic phenotypes. Some people make more androgens. Some people have a sustained stress response. Um, it's not very well studied, but it is very common-

    10. MB

      Yes

    11. AH

      ... uh, which I found interesting.

    12. MB

      Another reason why the carriers are so common is because typically there's no, no phenotype, or if there is, it's subtle, and so it doesn't come to the attention of any, any physicians. It's only when two defective copies of the gene come together in one offspring that there's no adrenal steroid production at all, and then things happen enough to get the attention of the doctors.

    13. AH

      Yeah, I've looked into this, and it, it does seem like, uh, one mutant copy of CAH is, is you find it just statistically, uh, more frequent in professions or sports where there's a requirement for, um, long-duration stress tolerance, which makes sense.

    14. MB

      Absolutely, yeah.

    15. AH

      Right? I mean-

    16. MB

      Yeah

    17. AH

      ... so some of these genes could confer an advantage.

    18. MB

      Yes.

    19. AH

      Some could f- confer a disadvantage-

    20. MB

      Right

    21. AH

      ... in different settings.

    22. MB

      And that there might be a heterozygote advantage. I mean, you know the classic example of sickle cell anemia, right, where, um, ha- being a heterozygote for that, uh, gene, uh, confers an advantage. If there's malaria in the area, you'll be less likely to succumb. Uh, things go wrong when two, uh, copies come together in one individual, and, and that's when the, the blood cells are especially affected. And things go wrong when an offspring gets two such copies, and which is relatively rare, but it does happen, and, and in that case, then, then the offspring are very sick.

    23. AH

      Did you ever do

  19. 1:35:41 – 1:41:32

    Birds & Sexual Differentiation, Gynandromorphs

    1. AH

      the head transplantation experiment on the finches?

    2. MB

      That, that's amazing what sort of a, a memory you have. No. No, I never did.

    3. AH

      You wanna explain what this was? Uh, uh, 'cause I'm not gonna do it correctly, but I remember you wanted to do an experiment-

    4. MB

      No [laughs]

    5. AH

      ... where you were gonna transplant finch heads.

    6. MB

      Well, pe-

    7. AH

      And I thought it was the coolest experiment ever, 'cause it was gonna be done as embryos.

    8. MB

      Yeah.

    9. AH

      So no, it was not taking heads off of birds.

    10. MB

      Yeah.

    11. AH

      Um, it was an embryo experiment, but I think-

    12. MB

      Well-

    13. AH

      ... we should talk about the backdrop of this. Male birds of certain species sing. Female birds don't.

    14. MB

      Right.

    15. AH

      So you wanted to embryonically put a female head on a male body, a male finch h- head on a female body, and you wanted to swap head bodies, uh, of these embryos.

    16. MB

      Oh, g- oh, y- yeah, yeah.

    17. AH

      Tell us the experiment, Marc.

    18. MB

      You, I mean, I'm, I'm certainly looking like, like the mad scientist. But it was, so-

    19. AH

      Oh, well, let me tell... Wait, wait, hold on. Crazier things have been done-

    20. MB

      Absolutely

    21. AH

      ... with US tax dollars, like-

    22. MB

      [laughs]

    23. AH

      ... brainbow mice, mice that glow, you know, 215 different fluorescent colors to identify different cell types. I mean, I could go on and on and on. I, I, I think, um, this experiment has a purpose to get at a principle that can't be u- understood any other way. So it's not just tinkering for the sake of tinkering.

    24. MB

      In fact, people do those sorts of transplants in birds. So a very famous neuroscientist from France, Nicole Le Douarin, uh, did these experiments where she would open up chick embryos and quail embryos, and she could scoop out part of the nervous system from one and implant it in the other, and she'd know when she had done it right, the, she had a way of telling the cells apart under a microscope. Plus, when they grew up, here you'd have this white Leghorn chicken with a streak of brown feathers right where she-

    25. AH

      Was it called a Quicken?

    26. MB

      Pard- [laughs] sorry.

    27. AH

      Couldn't help myself.

    28. MB

      Here you'd have this white Leghorn chicken with a, with a streak of brown feathers in the middle that were derived from the quail.And so it is possible to do those sorts of swaps. And of course, this is what's so great about working with birds, is their embryos are, you know, easy to get to for the first twenty-one days or so. Uh, so people had done those sorts of experiments. There was a question about sexual differentiation of the brain in birds because the... And I'll tell you why it turned out I didn't need to do that experiment and, and it wouldn't, wouldn't have shown what we wanted. Um, th-that is, so there are sometimes you'll see in the news, someone will find a gynandromorph in birds. Yep.

    29. AH

      Gynandromorph.

    30. MB

      Gynandromorph. So half female, gyn, and half male, andro. And when it happens in cardinals, for example, it's like the animal's been split down the middle.

  20. 1:41:32 – 1:45:31

    Anabolic Steroids, Hypersexuality; Adult Brain Plasticity

    1. AH

      Gonna give you two real-world examples. Real because, um, I was told them [chuckles] and I believe them. Um, in anticipation of our conversation today, I, I ventured into, um, some corners of the internet I kinda wish I hadn't. Um, but, you know, in, uh, gym culture, bodybuilding culture, th-there is a subset of people, I, I don't recommend it, that take, um, synthetic androgens, anabolic steroids of different kinds and in different combinations. And, um, again, I don't recommend people do this, um, uh, but it, it's entirely different than hormone replacement therapy or something like that. Like experimentation with high dosages of different types of testosterone derivatives. And my interest in understanding a little bit of what some of the general observations are there is this is a naturally occurring experiment with some thematic averages, which is geek speak for, like, if one person reports something, it means nothing, but if hundreds of people or thousands of people validate that experience, you think, "Well, this kind of-"

    2. MB

      Yeah.

    3. AH

      "...you know, these aren't controlled studies, but nonetheless might be interesting." And, um, those communities have, uh, long talked about how different forms of androgens, um, have different effects on psychology. And in particular, these days, you can find a lot of discussion, uh, um, i-in those communities of certain, um, anabolic steroids, uh, Trenbolone in particular, that causes aggression, but that is well known for, um, causing otherwise self-reporting as heterosexual males to start, um, wanting to have sex essentially with males or females. Um, this is an effect that seems reversible when they stop. Um, it seems generally associated with a kind of a hypersexuality.

    4. MB

      Yeah.

    5. AH

      Um, so that's an important variable, right? Um, so there's all sorts of variables there. So, so that's one observation that, um, that makes me wonder if the adult brain is still plastic at the level of the hypothalamus to androgens later in life. Now, this is not to say that the many, now millions of men who are taking testosterone replacement, which is very, very common, doing that safely with doctors', uh, support, et cetera, are, um, they're not trying to boost things into supraphysiologicalRange, but it's a naturally occurring experiment with very few controls and only anecdotal reports, but it suggests that the adult hypothalamus is still androgen sensitive in ways that can drive pretty powerful, um, changes in behavior and perception.

    6. MB

      And we know that is true because back in the previous century, Julian Davidson at Stanford actually, in the physiology department there, uh, was m- among the first to do these double blind placebo-controlled studies in men who had lost their testes for one reason or another, accident or cancer, things like that. And, um, and so double blind means neither the man nor the physician who was interacting with him had any idea whether he was getting the placebo or the testosterone. And that's of course really important for coming up with conclusions. And they concluded, uh, that in fact, the men who were getting testosterone definitely reported feeling better, feeling more energetic, having a higher libido, and they definitely felt better overall. And, and Julian said th- sort of the joke is that even though it was-- the men were supposed to be blind to which treatment they were getting, they always knew. They always knew when they were getting the testosterone because they felt so much better. So we know for certain that testosterone does have effects on the adult brain, uh, in many of these cases, right? These were men f- prostate cancer, uh, cases who were elderly yet and j- still, um, they still responded to that.

  21. 1:45:31 – 1:53:14

    Age & Testosterone Decline; Sexual Orientation & Activities

    1. AH

      Yeah. One thing I learned from your textbook-

    2. MB

      Oh, yeah

    3. AH

      ... um, was that, you know, this idea that testosterone diminishes with age is largely true, but the rates are, are highly variable and that, you know, there, there are some individual points on the scatter plot whereby you'll see somebody in their 70s or 80s whose testosterone is very similar to someone in their 20s or 30s. Now everyone nowadays talks about how testosterone rates are dropping, so it's a, you know, it's, these are older studies, but, um, it, it suggests that there's a tremendous amount of variation. Um, we also know that absolute numbers don't necessarily, uh, dictate how people feel. In fact, the CEO of a very, very, very successful company, uh, not a tech company, an entertainment company, w- came up to me once at a private party and said-

    4. MB

      Yeah

    5. AH

      ... that his testosterone was down in the low 300s, so this is approaching the lower end of the reference range, but he feels great. And I said, "If you're willing, like what variables are we talking about here?" And he explained, you know, vigor and he explained, um, you know, libido and he explained, you know, general enthusiasm for life and, um, and I said, "Well, I wouldn't change a thing in that case," right? I mean there's, he's a perfect case wh-whereby low end of normal is not a problem a- and who knows? Maybe had he taken more he would've aromatized more to estrogen and he wouldn't have felt as good for instance.

    6. MB

      Oh, no I agree. I mean if it ain't broke, you know, leave it alone.

    7. AH

      Yeah. I think it's something that doesn't get mentioned enough.

    8. MB

      And but you also point out why humans are such lousy research subjects because there's so much variability, uh, going on. Um, so what, what I can say is that, uh, for the decline in testosterone levels in men, uh, first of all it's so much more gradual compared to what happens to women at menopause, right? There's no comparison, uh, whatsoever and there is a incredible amount of variation across subjects and so, uh, once again even though you can say statistically we know this is a trend, I, I can't make-- y-you tell me a, a, someone 71 years old just to pick on me, I, I can't predict what their testosterone levels are gonna be like or not very well.

    9. AH

      Another, uh, sociological observation, uh, from the internet.

    10. MB

      Everything on the internet-

    11. AH

      Yeah

    12. MB

      ... is true.

    13. AH

      Certainly not everything on the internet is true. I know you were being sarcastic and certainly not everything on the internet is informative but, um, clusters and averages are, are interesting to me. Uh, there's a meme, um, which I find interesting, uh, vis-a-vis this type of conversation, um, whereby I, I think it was a, uh, a martial artist, a MMA guy from, from either Russia or, or some eastern country-

    14. MB

      Mm-hmm

    15. AH

      ... uh, excuse me. Um, the, the, the meme is, um, it goes something like s- uh, "Send two, three years Dagestan and forget." A guy is talking about how he wants his kid to be good at wrestling-

    16. MB

      That's what he is

    17. AH

      ... and so he's gonna send him to Dagestan where apparently the training is very intense and, um, and the meme goes, "Send two, three years Dagestan and forget." And he said, "I'm gonna send him there for a few, uh, weeks," and then, uh, and the guy goes, "No, no, no send two, three years Dagestan and forget." And that meme, um, which is a, i-it's not a cartoon it's a guy actually speaking-

    18. MB

      Yeah

    19. AH

      ... in that context has been you can find extensive compilations of people showing, um, kind of effeminate boys, um, dancing, doing kind of theater type activities and then, then, then it transitions to send two, three years Dagestan and forget. The idea being, returning to the beginning of our conversation, that, that there may be more plasticity early in life and that masculinization of behaviors stereotypically defined, okay? Want to be very clear. Um, the idea being that that's very plastic early in life. Okay. I think this is interesting and important to observe, um, because when I was a kid my mom, she tells, still tells me this story but she's told me this, verified this for many years.

    20. MB

      Okay.

    21. AH

      Uh, we had a pediatrician, um, this was in northern California. This is just a f- mile or two away from Stanford School of Medicine, um, and my pediatrician said to her, uh, "You, you have a boy, um, Andrew and there are three very important things in raising him," and these were his words. "One, don't let him ride motorcycles."

    22. MB

      [laughs] I, I agree. [laughs]

    23. AH

      "Two, don't let him drink soda. Too much sugar."Okay, fair. And he said, "Three, don't let him do theater."

    24. MB

      [laughs]

    25. AH

      The implication being that boys who do theater have a higher probability of becoming gay.

    26. MB

      Yeah.

    27. AH

      Now, that was... I was born in nineteen seventy-five, okay?

    28. MB

      Yeah.

    29. AH

      Um, he gave this advice to every parent of a male. Um, and I say that to kinda frame people's understanding of where we were versus where we are, and yet this meme is, I wouldn't say rampant on the internet, but has a fair amount of support for it in the sense that I think there's still the general belief that certain activities can bias sexual orientation. And I just wanna zoom out and a-ask, acknowledge the idea that the brain is plastic to androgens, behaviors impact androgens. So not trying to corral you into a given answer, but I think we've come a certain distance in this, but w-we haven't really come that far.

    30. MB

      Well, a-and, and of course, there's no doubt that the younger brain is more plastic. I mean, there's, there's no way around that. But, um, but, you know, in terms of what one can do, there are limits. And, and in terms of sexual orientation, I, I can tell you, people look really hard for any social correlates. You know, you, you talked earlier about the, the, the dad that's missing or, or even Freud talked about the overly coddling mother and, and the, the dismissive father, that that might make a boy more likely to be gay. And so people have looked for those sorts of correlates. The, the data just aren't there. I mean, it's really... Which, which I think is interesting-

  22. 1:53:14 – 2:02:35

    Marc’s Academic Journey, Ozarks, Luck

    1. AH

      The... Let's set the internet aside, and let's talk about a different upbringing for a moment, uh, which is yours.

    2. MB

      Oh.

    3. AH

      Um, as a-

    4. MB

      Yeah

    5. AH

      ... scientist, um, you have a somewhat unusual trajectory into science. So, uh, where were you born?

    6. MB

      Uh, i-in the Ozarks, in Springfield, Missouri.

    7. AH

      Oh, I was, I was about to say, "Where are the Ozarks?" I know where they are, but-

    8. MB

      Well-

    9. AH

      ... to orient our international audience. Yeah.

    10. MB

      Southern Missouri and northern Arkansas. So it's, uh, it, it's famous because it's hill country.

    11. AH

      Mm-hmm.

    12. MB

      And so very hilly, very much like the Appalachians, both in, uh, terrain and in culture, actually. Uh, so, no, I was born in the Ozarks in a, in a, a working class family. No one in my family had ever, um, uh... Well, no one in my mother's generation had finished high school, um, much less college. And, um, you know, I was always, um, a, a little bit different, um, because I was so much more interested in reading than, uh... All my cousins say that all they remember about me when we were growing up is I always had my nose in a book, right? That, that, that phrase. Um, so, uh, and I as, as I get... And I, I, I didn't choose that. I didn't choose to like reading, but I, I always did. Uh, and I always loved school, and, uh, so, uh, a-and, and I will say I had a great family that was incredibly supportive of me doing whatever I wanted to, right? That that would, that would be fine. Uh, and as I look back, I realize, and I, I predict you'll find this too, the older I get, the more I realize how much luck matters and how, how many very fortunate things happened to me, right? So, uh, the first question is, uh, I end up going to Yale College. What? Uh, working class fam... I m- Well, working class. So, so m-my folks were blue collar workers. I mean, for complicated reasons, I was raised by my grandparents. He was a construction worker, and she, she worked in a food processing plant. And, um, and so they once told me that maybe altogether they, they, they went to third grade, right? They got that far. But, uh, they were clearly smart and great people, and they were very supportive. And, uh, and so, uh, here's where... Here's an incredibly lucky episode that happened to me. So when I was a junior in high school, I go to the central high school library, and, uh, I, I volunteered there after work to put away books. And the librarian tells me, "Oh, there's this book you might be interested in." And she shows me this really thick paperback made out by the College Board. So this was the first year that the College Board had put together this book showing all the colleges in the United States with little blurbs about themAnd she said, "You might wanna look at that." And I open it up, and I see that for all the colleges, there's a paragraph about financial aid. So I read that entire book from front to back, except I only read the financial aid part. Or because at the time, my, my grandfather had passed away, and so my grandmother and I, our, our only income was Social Security, right? That was, that was, that was our livelihood. And um, and so I read financial aid, every one, and I get to the end. Uh, there, th- in this first edition, they were in alphabetical order, which makes no sense, but that's how it was. I get to the end, and the one for Yale College, it's like one of the shortest listings there, and it says basically, "We're committed to making sure everyone admitted will get the financial aid they need." This is me. This is what, this is where I need-

    13. AH

      You had to read the whole book just to get there.

    14. MB

      This is where-- Well, I, the, the next entry was Yeshiva, which I thought, "Well, that's a strange name," but if, if they'd had that paragraph, I-- Be-believe me, I would have been applying there, uh, which would have been fun too. And so I, so I go to my counselor, and I say, "Well..." And I'd never heard of Yale. I mean, I associated it with locks, right? I'd heard of Harvard because of Kennedy, but you know, nobody in my family talked... I go to my counselor, na- her name was Jean Walker, and, and, and she says, "That's an Ivy League school." "Huh? What does that mean?" And she, she, she tells me. And she-- And to her credit, she doesn't say, "That's stupid. You're never-- You know, why are you, why are you, why would you be doing that?" She says, "You know what? You should apply for early admissions this year." Early admission? I know. Okay. So I apply for early admission. I don't get in. So it's okay. But I'll try again next year because that paragraph's, it's, it's really got it under my skin, and this is what I need. So apply the next year, and this time, they ask me for an interview. And I'm, I'm to, I'm to have an interview with Dr. John Ferguson. I'm to call up his office and arrange for an interview. And I'm sitting in French class with my friend Dale, and I'm telling him I'm supposed to make an appointment with Dr. John Ferguson. And the French teacher, who was one of my letter writers, Mrs. Fisher, she overhears this, and she says, "What on earth? Why would you go see John F- Dr. John Ferguson?" Because she knew, but I didn't, he was an OBGYN, right? [chuckles] She-- And I, you know, sort of sotto voce, "Well, you know, da, da." "Oh, well, I know John. He's an old family friend. I used to babysit him. And you know, well, I'll be calling him." So I'm sure... I-I don't remember the interview with the man, right? I mean, I don't remember a thing about it, but I'm sure he told them I was, you know, the greatest thing on [chuckles] Earth be-because I mean, I'm sure he gave me as strong a recommendation as he possibly could. And, and so I-I got in, and they, and it-- They were true to their word. They submit, you know, this, send me this thick letter with all these, um, all this financial aid. And so, uh, and they didn't expect my family to contribute anything, right? So it was, it worked out. And, uh, and, and you know, and what ha- I have mixed feelings about Yale because I benefited so much. I mean, I... And I'll, I'll credit myself with this. I, I went with the right attitude, right? Which is, "They've made a mistake," [chuckles] right? "Mrs. Fisher got me in, and I'm, I'm not gonna screw this up." Uh, and, and indeed, you know, I w- I, you know, Andy, I wanna know everything. I, I wanna know about art and literature and all the sciences. It was j-- I mean, I, I was hungry, and I... So, and I went with the attitude is, "Man, all of these people are smarter than I am, and so I'm just gonna soak it up." And at least half of what I learned at Yale, I learned from other students, right? And the, the first night I'm on campus, you can, you can see what happened. So first of all, I drive from Springfield to New Haven. It's a long drive, but you know, that's how we go places. We, we drive. I get to New Haven, and it's, "Where am I gonna park this car? I can't..." I, I just thought, of course, there'd be, you know, parking lots, and there-- No. Yeah. And so I find a place in downtown, a garage, and oh, my God, this is gonna cost me so much money to keep the car here. I, I gotta take it back as soon as I can. And I go up to my, uh, my dorm room in the, in the old campus, and I meet my three roommates. And I know how to be sociable, so, "Where'd you go to high school?" And two of them tell me they went to prep school. "Huh? I-- What's a prep school?" And they explain that to me, and then they start talking about Phillips Andover versus Phillips Exeter. I don't know what... And, and, and the third guy, I, I, I won't mention the name, but, but his last name is one of, you know, generational wealth that every American has heard, right? So it's like, "Okay, I'm, I'm not in the Ozarks anymore." And then they start, you know, smoking dope, and I've never seen that before, right? I've never, I've never, I've never been around people smoking marijuana before. And they assure me, "Oh, the campus cops, they'll look the other way." And I'm thinking, "What?" And, and that very summer in Greene County, where I'm from, a s- a judge had sentenced a young man for possession of marijuana, had given him a life sentence.

    15. AH

      Whoa.

    16. MB

      This is, this is-

    17. AH

      For possession of, of weed?

    18. MB

      This, this is 1972, and this is the Ozarks, right? Not, not the same sort of place. So I'm thinking, "Well, maybe the campus cops would overlook you smoking dope, but I'm not gonna give Yale any excuse to send me home." It was like a kid in a candy shop. And because I regarded everyone there as, as-- They certainly knew more than I did, all of them, um, and, and they were probably smarter than I. I-- It was like I, I never felt the pressure to be the smartest person in the room, right? Okay, I'm not. I don't care. I'm-- And I, I took as many classes as I could, uh, and [chuckles] you know, uh, I, I own-- I always wanted to take six... You were supposed to take no more than five courses per term, and so I, I, I would always wanna take six, and the dean wouldn't let me. So I'd take five courses and, and a lab, which is like half a course, et cetera, um, and I'm just, you know, ha-- I'm not getting A's in everything, but I don't care, right? I didn't f- so, uh, I'm having a great time, uh, and that's when I learned about neuroscience.So first someone told me, "Oh, look at this course about comparative psychology." What's comparative psychology? It means comparing across species. And oh, I didn't know psychologists studied animal behavior. And then pretty soon I, I took a class, uh, Linda Uphouse taught, a physiological psychologist, taught neuroscience, and I'm hooked, right? I mean, this is... I love this stuff.

  23. 2:02:35 – 2:08:47

    Exploration; Kids & Sex Differences

    1. AH

      I mean, it's been a, an amazing arc to go from the Ozarks to Yale. I love that when you found yourself in an environment that offered a lot of opportunity, that you seized that opportunity. I think, um, many people wouldn't have done the same had they not had your background, but maybe even if they had. I mean, it's-- I think that when you find yourself in a place where there's tons to learn and you throw yourself into that, uh, only good things can come of that. I mean, you mentioned luck, but I think, you know, luck is, I wouldn't say evenly distributed, but it, but it has a, a, a habit of, of finding the prepared, as they say, right? I obviously didn't make that statement.

    2. MB

      Right. Right.

    3. AH

      So, and I, and I love this theme of, of exploration. I mean, we... You know, I think of you as the hormones and sex behavior, hormones and, uh, sexual orientation scientist, right? But I also remember, you know, and it was twenty-five years ago, that, um, you always walked very quickly and you always had an idea that you were excited about whenever I'd run into you. So I wanna say you, you've really inspired my career to go after things that interested me and, and just really follow those trails, and also when, when it wasn't so clear what to do, um, to pick the thing that at least was most exciting then and not worry about where that was going to lead next. You strike me as one of the least careerist people I've ever met. Like, um, and I, I also acknowledge you've had a spectacular career, and it's still going. I mean, your name is synonymous with hormones and behavior and hormones and sex behavior. You're being humble now, but it's, it's absolutely true. It didn't hurt that your last name was Breedlove [laughs] -

    4. MB

      Yeah

    5. AH

      ... if I'm honest. But, uh, let's face it, that wasn't gonna confer you, uh, like, a real lasting advantage, so clearly you've put in the work. I also really wanna thank you for coming here today and, and teaching people what's known about these topics, and these are not easy topics to parse. The languaging has to be very specific. The reason it has to be specific is in one part political, sort of, but it's really about making sure that people understand what's true, what's not true, and what's not known yet, so that they can form their own ideas and, and I really admire the way that you're able to do that. And I also learned a ton today. So, you know, I'm struck by a number of different things in this model of how we become who we are. And as someone who's raised kids successfully and, um, now has grandkids-

    6. MB

      Yes. Two

    7. AH

      ... um, I knew your kids, so that's a trip to me. I haven't seen them in years. But they have kids. I, I think, um, maybe you would just comment briefly on, you know, did you observe early sex differences in terms of behavior? Did... Was it striking? Did you do experiments on your kids or did you opt not to?

    8. MB

      It was pretty amazing, really, now, now that you mention it, because, um, Steve Quickman once told me that there was... Someone did a study where you ask people, "How much do you attribute personality to nature and how much to nurture?" And, and he said the only correlation that came out of it was the more kids people had, the more they thought nature was important for, um, for determining... And, and you know that because if you have more than one kid, they're not the same. And so in, in, in terms of sex differences, I'll tell you. So I have one daughter, Tessa, and, you know, she had two older brothers, et cetera. And, you know, you know, my partner, Cindy Jordan, she... Neuroscientist, too, and, um, she almost never wore dresses, right? That would be... Or a skirt. That was just, you know, not useful around the lab. And there was a period there where every day with Tessa, it was, it was a struggle if we didn't put her in a dress, right? She really wanted to wear... And as soon as she could walk, one of the things she liked to do was to put on her mother's various shoes, right? And walk around in them. Cute, etc. Um, I mean, she was so different from the beginning. Now, I'm not a biological determinist. I don't think, you know, I don't think biology is everything. I don't think, you know, prenatal things are everything. There's no, there's no one cause of any human behavior. But it, it really struck me. Oh, and, and one of my boys could make a gun out of anything, right? [laughs] We, we, you know, this is an era where we're trying not to-

    9. AH

      Even growing up in Berkeley.

    10. MB

      Oh, my. Well, especially in Berkeley, 'cause he wasn't gonna find a toy gun, but by, by golly, he could make one. Uh, and, and he was also the, the, the kid that, that, you know, loved any toy with wheels on it, right? So it was... And, and you know, even among monkeys, right? Melissa Hines, uh, showed it first. Even among monkeys, if you put in wheeled toys, it's the male monkeys that are much more interested in that than the females, and the female monkeys are much more interested in, in the dolls, et cetera. Um, so yeah. You, you have more than one kid, I, I predict you're gonna be amazed about how, you know, how different the kids are, even though you're the same family, right? They don't all come out the same.

    11. AH

      Once again, you've been a huge inspiration to me over the years, and I know that the listeners are greatly appreciative of everything you've taught, and we gotta get you back here. Oh, also, you're writing a book-

    12. MB

      Yes. Yep

    13. AH

      ... about the biology of sexual orientation.

    14. MB

      Yep. I'm, I'm trying.

    15. AH

      I didn't know this. We don't do... We actually don't really do book promos. That's not really the, our podcast, but when, when can we expect that book to hit the shelves?

    16. MB

      Oh, you put me in such a tough spot. So I, I, I'm, I'm struggling with it. I've, I've written six chapters and I'm, I'm intending t-there be 11. My goal is, can I get this first draft done by this fall? And then there, you know, there's reviewing and things like that that'll happen. So I do, you know, knock on wood, I'm, I'mI'm really hoping I'm going to finish this book. And, and if so, uh, well, you know, I expect you-- since, since you owe me so much, I expect you to buy a copy.

    17. AH

      Absolutely. I'll buy a copy, I'll read it, and I'll let the world know what I think about it. Dr. Marc Breedlove, thanks for coming here today. Come back again.

    18. MB

      It was a pleasure. I've had a great time.

    19. AH

      Thank you.

  24. 2:08:47 – 2:11:16

    Zero-Cost Support, YouTube, Spotify & Apple Follow, Reviews & Feedback, Sponsors, Protocols Book, Social Media, Neural Network Newsletter

    1. AH

      Thank you for joining me for today's discussion with Dr. Marc Breedlove. To learn more about his work, please see the links in the show note captions. If you're learning from and/or enjoying this podcast, please subscribe to our YouTube channel. That's a terrific zero-cost way to support us. In addition, please follow the podcast by clicking the follow button on both Spotify and Apple. And on both Spotify and Apple, you can leave us up to a five-star review, and you can now leave us comments at both Spotify and Apple. Please also check out the sponsors mentioned at the beginning and throughout today's episode. That's the best way to support this podcast. If you have questions for me or comments about the podcast or guests or topics that you'd like me to consider for the Huberman Lab Podcast, please put those in the comments section on YouTube. I do read all the comments. For those of you that haven't heard, I have a new book coming out. It's my very first book. It's entitled Protocols: An Operating Manual for the Human Body. This is a book that I've been working on for more than five years, and that's based on more than thirty years of research and experience. And it covers protocols for everything from sleep to exercise to stress control, protocols related to focus and motivation, and of course, I provide the scientific substantiation for the protocols that are included. The book is now available by presale at protocolsbook.com. There you can find links to various vendors. You can pick the one that you like best. Again, the book is called Protocols: An Operating Manual for the Human Body. And if you're not already following me on social media, I am Huberman Lab on all social media platforms, so that's Instagram, X, Threads, Facebook, and LinkedIn. And on all those platforms, I discuss science and science-related tools, some of which overlaps with the content of the Huberman Lab Podcast, but much of which is distinct from the information on the Huberman Lab Podcast. Again, it's Huberman Lab on all social media platforms. And if you haven't already subscribed to our Neural Network Newsletter, the Neural Network Newsletter is a zero-cost monthly newsletter that includes podcast summaries as well as what we call protocols in the form of one- to three-page PDFs that cover everything from how to optimize your sleep, how to optimize dopamine, deliberate cold exposure. We have a foundational fitness protocol that covers cardiovascular training and resistance training. All of that is available completely zero cost. You simply go to hubermanlab.com, go to the Menu tab in the top right corner, scroll down to Newsletter, and enter your email. And I should emphasize that we do not share your email with anybody. Thank you once again for joining me for today's discussion with Dr. Marc Breedlove. And last but certainly not least, thank you for your interest in science. [outro music]

Episode duration: 2:11:17

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