Peter Attia MD374 - The evolutionary biology of testosterone: male development & sex-based behavioral differences
EVERY SPOKEN WORD
120 min read · 24,430 words- 0:00 – 0:11
Intro
- PAPeter Attia
[upbeat music] Hey, everyone. Welcome to the Drive podcast. I'm your host, Peter Attia. [upbeat music]
- 0:11 – 8:25
How Carole became interested in exploring the biological & evolutionary roots of sex differences & the role of testosterone
- PAPeter Attia
Carole, thank you so much for coming out to Austin. Great to, great to meet you in person.
- CHCarole Hooven
Thank you so much for having me. I'm thrilled to be here.
- PAPeter Attia
This is a topic that we, we talk a lot about on the podcast, but usually from a pretty narrow lens, right? Which is in the form of replacement. Um, we talk about hormones, um, both in men and women, uh, sex hormones, and we talk about how they, they wax and wane as a, as an individual ages. We obviously then talk about, you know, sort of the medical use of them. But I don't think we've spent any time understanding the more basic fundamentals of these hormones, the role they play in our evolution. Um, and anecdotally, I, y- you know, I, I'll, I'll just share with you kind of the observation that any parent probably has, uh, if they have male and female children, right? So my, my first child was a girl, and I, we-- my wife and I very, very stupidly and arrogantly thought we were the perfect parents because, like, she was so well-behaved.
- CHCarole Hooven
[laughs]
- PAPeter Attia
And we were like, "What do all of these other parents with their boys running around misbehaving, like, what are they doing wrong?" And like, "How could we-
- CHCarole Hooven
[laughs]
- PAPeter Attia
"... teach them how to be as good as we are?"
- CHCarole Hooven
Yeah.
- PAPeter Attia
I mean, we didn't actually say that, but there was undoubtedly an annoying smugness to us. Um, and if you believe in a god, that god smacked us into our place with two boys that followed, who were, for all intents and purposes, treated the same way, socialized the same way, and there is a level of aggression in them, a fury in them-
- CHCarole Hooven
[laughs]
- PAPeter Attia
... that I've never seen, probably unless I were to go back and hear stories of what my mom said I was like.
- CHCarole Hooven
How old are your boys now?
- PAPeter Attia
Uh, eight and almost 11.
- CHCarole Hooven
Okay.
- PAPeter Attia
And they're a dif-- they're not, I wouldn't say they're a different sex. I would say they're a different species.
- CHCarole Hooven
Yeah, I was just gonna say that.
- PAPeter Attia
Yeah. So all of that is to say, I don't, I don't feel we did anything different, and yet they couldn't be more different. And I, I appreciate that that's not gonna be the case for every parent. Um, but I also don't know how much-- Well, I, what I hope to learn is how much testosterone has to do with that, because I also am under the impression that at this age, the testosterone levels wouldn't be that much different. And I understand and we'll probably talk about the differences in testosterone levels during the embryologic phase, because obviously, that led to the differences. But anyway, with that as backdrop-
- CHCarole Hooven
Yeah
- PAPeter Attia
... how did you get interested in this topic?
- CHCarole Hooven
Great. Okay, so I wanna make sure to come back to everything that you just said. Um, so how did I get interested? I'm gonna start at the beginning, which is that I grew up with three older brothers, and I'm assuming that this had something to do with my interest in testosterone. We-- They were different than I was, I am, in some pr- in some consistent ways. I don't think I thought much about that. And I think that probably made me really wanna understand what motivates, um, male behavior in general, and why it's different from female behavior. That wasn't sort of an idea that I had when I was in college that I was gonna go study this, but I did become intensely interested in the evolutionary origins of human behavior in general, and what makes us different from other animals. And that happened, I think, because of traveling. I traveled, uh, to a lot of different places in the world, mostly by myself, uh, during and after college, and there were such extreme differences culturally. Egypt was-- Your family's Egyptian?
- PAPeter Attia
Yep.
- CHCarole Hooven
That was one of the places I went that really freaked me out [laughs] because I-- that really shook me, um-
- PAPeter Attia
Say more
- CHCarole Hooven
... because the cultural differences were so profound in terms of the incredibly important role that sex plays in social life, and the segregation, uh, and different rules that applied to males and females. I was, I was alone, traveling by myself as a young woman, totally ignorant of what I was getting into in Egypt. I was harassed endlessly. Um, some of that was my fault for not understanding the culture well enough and what I was getting into. Uh, so this combination of w- being immersed in not only different societies that treated sex and sex roles very differently, but also different ecologies. I spent some time, um, in Africa and Kenya and Tanzania and got really interested in all of the animal behavior and why we are different from other animals, et cetera. So I had a whole other career before graduate school, and I ended up leaving that career and applying, uh, to Harvard to try to do a graduate degree where I could, um, do more to understand the evolutionary basis of human behavior. I ended up, uh, getting rejected, and I just persisted, and then was offered this job out in Uganda studying chimps for what was supposed to be a year. And that is what really triggered my interest in sex differences and testosterone. Because we, I think to a certain ex- extent, are indoctrinated, uh, to believe that most human sex differences are cultural, or if you think that they're not It's better you don't say that out loud to too many people or in the wrong place. Uh, so when I spent time with the chimps, I was really blown away by the ways that the sex difference in the ch- sex differences in the chimps paralleled human sex differences. Of course, not exactly the same, but the very basic things that you just described, um, even just in terms of energy and aggression, are present in the chimps in terms of being higher in the males and lower in the females. And I'm getting goosebumps because the reasons for that are so profound and far-reaching and start with sperm and egg, and that's what sex really is about, is the, um, not just the ability to produce sperm or eggs, but kind of the way that the organism is designed and the, uh, reproductive phenotype, including body and behavior. And then that, in humans, plays out in these really complex ways in terms of social systems. So I th- I really, I got interested in testosterone because this is one thing I could grab onto that links very clearly humans, chimpanzees, and every other mammal in terms of, um, males having much higher levels than females. And it's not just mammals. There are other forms, um, of steroid hormones that, uh, other species have, but this is, um, pervasive and just a very powerful way to understand proximately, that means what's happening sort of here and now in the organism, why the sexes are different. And then there are these deep evolutionary pressures that have to do with reproductive strategies for organisms that produce sperm versus organisms that produce eggs. And so then I ended up, uh, reapplying to Harvard and getting into the grad program there, and I did my dissertation on testosterone and sex differences in cognition, um, and the way we think and process information, and I had men watch sexy videos and also videos of dental surgery and collected [laughs] uh, their saliva and measured their testosterone in the lab. And, uh, and then I just stayed on at Harvard, uh, mostly just teaching.
- PAPeter Attia
So, uh, I
- 8:25 – 11:09
How testosterone & other hormones influence sex differences in aggression & behavior across species
- PAPeter Attia
wanna go back to something you, you, you sorta said a second ago, which is the distinction between mammals and non-mammals. Uh, and I never really thought of it until you said this, but if, if I were to look at a, a male great white shark and a female great white shark, first of all, do they have testosterone in them as the androgen or sex hormone?
- CHCarole Hooven
So vertebrates, most vertebrates will have testosterone-
- PAPeter Attia
Okay
- CHCarole Hooven
... or something very, very close to testosterone, yep.
- PAPeter Attia
Now if you, again, go back to the example of great white sharks-
- CHCarole Hooven
Yeah
- PAPeter Attia
... typically the females are larger. I would reckon they're just as aggressive as the males. Is that reflected in comparable levels of testosterone in those species?
- CHCarole Hooven
So sharks I don't know about specifically, but first of all, m- uh, males are not always bigger than females. Males will do whatever they need to do generally to compete for mates, and in many species it's not, uh, to be larger. Also, there are differences in the ability to defend a territory or defend mates in air and water and land, and th- that's really a interesting way to understand some male competitive strategies. So but generally, when in the species, if the female is just as aggressive, often it's, uh, maternal aggression and not necessarily, uh, mate competition.
- PAPeter Attia
Mm-hmm.
- CHCarole Hooven
And if it's, uh, maternal aggression tends to be mediated more by estrogen than testosterone. Even in hyenas, that, uh, which are very difficult to tell apart. The females are very difficult to tell apart from the males. They have this clitoris that looks exactly like a penis, and experts often can't even tell the difference. They're highly aggressive. Uh, and that seems not to be mediated by adult, in the adult at least, with, uh, by comparable levels of testosterone. There seems to be potentially something going on in early development. But often I, I don't know of good evidence that testosterone acts similarly in females to mediate, um, say, mate aggression that's, we'll say mating aggression, something like that.
- PAPeter Attia
So, so just make sure I understand. In the hyenas, if you took-
- CHCarole Hooven
Yeah
- PAPeter Attia
... an adult male and an adult female hyena, would they have similar levels of testosterone and estrogen?
- CHCarole Hooven
No. No.
- PAPeter Attia
The f- the males would be higher.
- CHCarole Hooven
The males, the males would be higher, um-
- PAPeter Attia
Despite the fact that phenotypically they look the same-
- CHCarole Hooven
Yes
- PAPeter Attia
... and they're both equally aggressive.
- CHCarole Hooven
I believe they're either just as a- aggressive, if not more so. I think they're, I believe that they're dominant to the males.
- PAPeter Attia
Got it.
- CHCarole Hooven
Uh, and there's something going on-
- PAPeter Attia
Yeah
- CHCarole Hooven
... with potentially adrenal androg- like maternal adrenal androgens when the fetus is developing that becomes the aggressive female, but I don't think it's, uh, completely worked out. I haven't looked at the literature on that in ages.
- PAPeter Attia
So the,
- 11:09 – 20:04
How chromosomes, the SRY gene, & early hormones direct embryonic sexual differentiation
- PAPeter Attia
the extent of my recollection from, um, from medical school on this topic was that, and again, we can come back and talk about the edge cases, but 99.9% of cases are either XX or XY, right? In terms of humans.
- CHCarole Hooven
In humans, yes.
- PAPeter Attia
Yeah, yeah, right. So we can talk about Turners and Klinefelters and things like that later. But in the 99.9% of cases of XX and XY, what are the steps, and, um, how do they involve sex hormones that create the phenotypic differences in the embryo?
- CHCarole Hooven
Yes. So phenotypic, um, we'll just stick to the body, and then we can also talk about the behavior.
- PAPeter Attia
Yes, yes, exactly. That's what I want-
- CHCarole Hooven
Yeah.
- PAPeter Attia
I just wanna start with let's get through the first nine months. [laughs]
- CHCarole Hooven
Yeah.
- PAPeter Attia
And then, like, let's help understand how those, those... Two options of chromosomes-
- CHCarole Hooven
Sure
- PAPeter Attia
... lead to two different body types.
- CHCarole Hooven
Sure. And I just wanna say right at the outset that we have a sex determination system that relies on chromosomes, but not every animal does. So chromosomes do not equal sex, and birds have used chromosomes, but they have a, a different system where the female is the one that has heterozygotic-
- PAPeter Attia
Mm-hmm
- CHCarole Hooven
... um, chromosomes. So there's temperature-dependent sex determination, so people should not confuse, uh, the sex hormones themselves with the definition of sex. However, they do-
- PAPeter Attia
The chromosomes or the sex hormones?
- CHCarole Hooven
Sorry. Th- sorry, sorry, did I say sex hormones?
- PAPeter Attia
Yeah.
- CHCarole Hooven
Sex chromosomes.
- PAPeter Attia
Yes, yes.
- CHCarole Hooven
Sorry. Uh, thank you. So se- the, in, in mammals, the chromosomes determine sex but do not define sex. Again, across sexually re- m- almost all sexually reproducing organisms, it's the, um, gamete type that the organism is basically designed around, uh, the re- that the reproductive system is designed around that defines sex. So and also we can h- other organisms have, um, can be hermaphroditic, have, uh, produce both gamete types at the same time, or they can be sequential hermaphrodites, so I just wanna-
- PAPeter Attia
Yep
- CHCarole Hooven
... get that out first. So in humans, the, uh, mom, the m- mother's egg is always the, the sex chromosome is always going to be an X that it donates, um, in its egg, and it's gonna combine with a sperm. 50% of the sperm are gonna have a Y sex chromosome, and 50% of the sperm are gonna have a X chromos- uh, gonna have an X in general. So those two, uh, combine, and the developing embryo is gonna be either XX and XY. So let's just start with the XY. Uh, so you were an XY. I had a son who is an XY, which is weird for women because they ha- they will have a, something inside of them that has testicles that's producing, that produce testosterone, uh, which I think is interesting. And so an XY fetus around, uh, five or six weeks... S- I should just say that XX and XY are both, uh, almost completely, they're almost identical until that time.
- PAPeter Attia
Sure.
- CHCarole Hooven
And the Y chromosome has a gene on it called the sex-determining region of the Y chromosome that produces a protein called the SRY protein, and this is a very important protein because it triggers the differentiation of the undifferentiated gonad. So what's really cool and interesting is that before that time, we all have a gonad that can become-
- PAPeter Attia
Both
- CHCarole Hooven
... either one. It can become, um, testes or it, it can become ovaries, and that's sort of an amazing design. That's evolution's way of not wasting energy, not hav- having to have two-
- PAPeter Attia
Two systems
- CHCarole Hooven
... two different systems-
- PAPeter Attia
Yeah
- CHCarole Hooven
... that one develops and the other gets discarded, at least in terms of the gonads. So they come first, and so in terms of sexual differentiation, that means that for XY, um, individuals, the gonads are gonna develop along the testicle route. And without the SRY gene, they will, by default... Y- wh- when I say by default, that doesn't mean that nothing else has to happen. Other genes have to be expressed, and, and that's an active process. It's not a passive process. But without the SRY gene, those undifferentiated gonads will differentiate in the female direction to form ovaries.
- 20:04 – 23:43
A stark contrast of male social bonding compared to females
- PAPeter Attia
just gonna-
- CHCarole Hooven
... constraint
- PAPeter Attia
... take you down a stupid detour-
- CHCarole Hooven
[laughs]
- PAPeter Attia
... for your next book. Um, we were at my younger son's, uh, baseball party at the end of the season.
- CHCarole Hooven
Yeah.
- PAPeter Attia
And so now picture at the, you know, at the time, a bunch of, I don't know, 27 year old boys running around the pool playing baseball, playing football, goofing off, and me and the dads were sitting there hanging out, and we were observing their behavior and, and I came up with this observation, which is there's, um, estimated to be about 110 billion humans that have lived, right, over the past 250,000 years, inclusive of, of course, the eight or so billion that are alive today. And just watching this small group of 20, you could already see the number of times one boy would walk up to the other and sort of flick him in the nuts, okay?
- CHCarole Hooven
[laughs]
- PAPeter Attia
And I was like, "All right," to the dads-
- CHCarole Hooven
What? [laughs] Oh
- PAPeter Attia
... "How many times, how many times in the history of 250,000 years has one male gone up-
- CHCarole Hooven
Yes
- PAPeter Attia
... to another male to flick him in the nuts? How, what's that number?"
- CHCarole Hooven
So it go- it goes back... So the chimps did this.
- PAPeter Attia
Well, th- so but let me finish the punchline.
- CHCarole Hooven
Yeah, sorry, sorry.
- PAPeter Attia
The punchline is whatever that number is-
- CHCarole Hooven
Yeah
- PAPeter Attia
... it's enormous.
- CHCarole Hooven
Yeah.
- PAPeter Attia
Now, what's the number of females that have gone up to another female and gone bing and tried to flick them in the clitoris? Like zero.
- CHCarole Hooven
Zero.
- PAPeter Attia
Exa-
- CHCarole Hooven
There is sometimes a little breast play-
- PAPeter Attia
Yeah
- CHCarole Hooven
... [laughs] I guess-
- PAPeter Attia
But it's like-
- CHCarole Hooven
... with teenagers, but nothing like what, what boys do
- PAPeter Attia
... how, how is this po-
- CHCarole Hooven
What men do
- 23:43 – 34:20
How hormones like DHT shape sexual differentiation, & how 5⍺-reductase deficiency reveals the distinct roles of these hormones
- CHCarole Hooven
Um, so I'm just gonna go through the ducts a, a little more quickly.
- PAPeter Attia
Yeah.
- CHCarole Hooven
That's n- th- there's two different systems. So the Wolffian ducts become what I'll just say is the male internal plumbing, and the, um-
- PAPeter Attia
Mullerian
- CHCarole Hooven
... Mullerian ducts become what is the female internal plumbing. So what's, what's important is that the Leydig cells produce testosterone, which stabilizes the development of the Wolffian ducts. The testicles have to produce, uh, two hormones. Leydig cells produce testosterone to stabilize the Wolffian ducts s- to connect the, um, sperm-producing organ to the delivery system ultimately-
- PAPeter Attia
Okay
- CHCarole Hooven
... which is the penis, and they have to cause The degeneration of the Mullerian ducts, so that's anti-Mullerian hormone and testosterone. So healthy testes, and this is important when we talk about, uh, the disorders or differences of sexual development, healthy testes will have those effects. And you can also think about, well, what happens if they can't produce anti-Mullerian hormone, or what happens if there's no receptor for testosterone or nor- no receptor for Mullerian hormone.
- PAPeter Attia
And by the way, is there, at any point, is any of this testosterone being converted to DHEA in any meaningful amount?
- CHCarole Hooven
Not that I know of. DHT for sure.
- PAPeter Attia
Yep.
- CHCarole Hooven
That's extremely important, and that comes next. Uh, so I would like to talk-
- PAPeter Attia
Sorry, I meant DHT.
- CHCarole Hooven
Yeah.
- PAPeter Attia
So I'm sorry. I'm sorry.
- CHCarole Hooven
Okay.
- PAPeter Attia
Yeah, yeah, yeah, yeah.
- CHCarole Hooven
So I w- I wanna make sure... Maybe I can just talk a l- about it a little bit now. Uh, so, so that conversion is via the enzyme 5-alpha-reductase-
- PAPeter Attia
Yep
- CHCarole Hooven
... that's president, that's present in, uh, high concentrations in the genital tissue. So what's interesting about this is that you have a mechanism to achieve high concentrations of a more potent androgen without that, uh, having to circulate through the general circulation-
- PAPeter Attia
Got it
- CHCarole Hooven
... which you do not want in a developing fetus. You wanna be able to control, um, the development of the penis, say, which is one of the things that DHT does. It takes the, um... So the, so the genital tubercle can become the clitoris or the penis, essentially, in the presence of testosterone and functional, uh, 5-alpha-reductase. It becomes a penis. The labia grow and then fuse to become the scrotum. Uh, and that, and also the prostate. The, uh, DHT is necessary for full prostate development and can later, uh, sustain the function of the prostate. So what's... It, it is interesting because it is this solution to an- to providing very strong androgenic signals in the tissues that need it without wasting energy on str- uh, strong androgenic signals in the rest of the body.
- PAPeter Attia
And so is that... I've never actually under- I've never thought about this until now. Is that why DHT has such a high affinity for the androgen receptor, you think?
- CHCarole Hooven
Yes.
- PAPeter Attia
Is so that you could permit it to only have a local effect-
- CHCarole Hooven
Yes
- PAPeter Attia
... during embryologic development? 'Cause otherwise, I don't know that it would matter as much in, in me at this old age-
- CHCarole Hooven
Yeah
- PAPeter Attia
... that DHT is that much more potent than testosterone, right?
- CHCarole Hooven
So I don't think it would matter as much, uh-
- PAPeter Attia
Because I'm, I'm-
- 34:20 – 47:13
How sex chromosomes & prenatal testosterone shape early brain development & explain sex differences in childhood behavior
- CHCarole Hooven
So the production of testosterone in the testes, this is really important and just fundamental to understanding sex differences. It's not that we have so many different genes. So at the same time, I should say, there i- we're learning more about the role of the 70 to 100 genes on the Y chromosome, many of which are crucial for, uh, typical development of male, uh, reproduction and, and reproductive function. Uh, but also it appears that there's some role even prior to the production and action of testosterone on the body and brain. The, there may be early expression of genes on the Y chromosome that act in the brain to shape later patterns of behavior. Uh, so that, there's a lot of work going on there to understand that. Excuse me. Um, so there are genetic differences, and I also wanna say that the genetic differences don't just stop at the differences with those genes on the Y. Uh, all the other genes are the same except for the sex chromosomes. But having one X versus two Xs makes a huge difference. It's extremely important. Uh, so typically, so people think that the, that females completely silence one of their X chromosomes, uh, in each cell, which is something that basically does happen so that we don't have a double dose of X chromosome genes compared to males. So that's something called the Barr body.
- PAPeter Attia
But if that were true, then wouldn't ... It must be more complicated or else-
- CHCarole Hooven
It is
- PAPeter Attia
... you wouldn't have Turner syndrome.
- CHCarole Hooven
It is. So, yes. So what happens is ... And that's right, and we can talk about Turner syndrome, but, uh, something like 20%, and here someone might correct me, but I think around 20% of the genes on the silenced X escape inactivation, and that turns out to be important that there are some genes in females that need, where, where the female needs the double dose of those genes, and if she doesn't have the double dose- As in, uh, Turner syndrome. That's a, uh-
- PAPeter Attia
Which we can define for folks as single X chromosome-
- CHCarole Hooven
That's right
- PAPeter Attia
... which presumably they got from mom, and then they didn't get a chromosome from dad. Or do we know that?
- CHCarole Hooven
They can get it from mom or dad.
- PAPeter Attia
Got it.
- CHCarole Hooven
And that's another rabbit hole we could go down. There are imprinted genes, uh, [lips smack] depending on the, the pa- parental origin-
- PAPeter Attia
Wow
- CHCarole Hooven
... meaning certain genes are preferentially expressed or suppressed in the mom's X versus the dad's for interesting evolutionary reasons, because the mom and dad have, uh, competing interests in what happens to the kid. [laughs]
- PAPeter Attia
And phenotypically, a woman with Turner's syndrome does appear phenotypically female.
- CHCarole Hooven
Yes.
- PAPeter Attia
But I believe she's not able to reproduce?
- CHCarole Hooven
That's correct, as far as I understand. I think that there's some evidence that there's technology now where, where they could reproduce-
- PAPeter Attia
Oh, so she's not f- but she's sterile under maybe natural conditions.
- CHCarole Hooven
In some case- I think in some rare cases-
- PAPeter Attia
Okay
- CHCarole Hooven
... that can happen.
- PAPeter Attia
Yeah.
- CHCarole Hooven
But generally, the ovaries don't, uh-
- PAPeter Attia
But her stature is distinctive.
- CHCarole Hooven
It's short.
- PAPeter Attia
Right? She's gonna be shorter.
- CHCarole Hooven
Yep. And there's those sort of-
- PAPeter Attia
There's a sort of wider neck-
- CHCarole Hooven
Yeah
- PAPeter Attia
... and a few other, uh, characteristics.
- 47:13 – 55:04
How gamete differences shape reproductive strategies, energetic costs, & sex-specific behavior
- PAPeter Attia
Define that again, 'cause I, I, I wanna make sure the listener understands when you're referring to gamete what you're talking about-
- CHCarole Hooven
Sorry
- PAPeter Attia
... and the production of them. Yep.
- CHCarole Hooven
Sperm and eggs.
- PAPeter Attia
Yep.
- CHCarole Hooven
So what road are... What does evolution... How... What has evolution designed you for? If you're XY, and you're going to be making sperm, and that, uh, there's gonna be a suite of characteristics generally that are gonna be different from the suite of characteristics that a female who has egg, who's, has ovaries and eggs will need to maximize reproduction. So all evolution cares about is how many, uh, uh, what portion of your genes are making it into future generations. So the design here is about reproductive strategies that coordinate how your body grows, what your body is like, what physical features you develop, coordinates, uh, the hormones, coordinate that with certain, um, patterns of behavior on average. Every, all of the, the bodies and the behavior can vary across XX and XYs, but what we're talking about is these broad patterns mostly to do with sex and aggression that tend to differ between males and females. So it's really all... And this is across sexually reproducing organisms for the most part. So all the other stuff can vary. It's not that, like, all XY people are going to have a higher sex drive and be some, more aggressive. That's just not the case. It's, uh, bodies vary, behavior varies.
- PAPeter Attia
I know you weren't consulted during the design phase-
- CHCarole Hooven
[laughs]
- PAPeter Attia
... but do you have a sense of why The female gametes are all produced up front.
- CHCarole Hooven
Oh, God.
- PAPeter Attia
And you, you basically get your lot at birth, and then you... That's it. It's a rate of attrition versus why the male gamete is just produced on demand. 'Cause I mean, again, I'm being a bit facetious. Of course, we don't-
- CHCarole Hooven
Yes
- PAPeter Attia
... know this, but do you, do you have an insight into why-
- CHCarole Hooven
I have-
- PAPeter Attia
... that's the case?
- CHCarole Hooven
I, I'm sure there's a better answer, but here's what I think, and I, um, and I hope people will write in with the better answers. Making eggs is expensive calorically and, and in terms of time and calories, it, they're expensive. And organisms-- So what we are designed to do is convert energy into offspring. That's basically what evolution-
- PAPeter Attia
[laughs]
- CHCarole Hooven
... uh, put us here to do, and you wanna do that as efficiently as possible. So eggs are energetically expensive. Sperm is less energy, uh, energetically expensive, and I don't know what happens in terms of how the eggs that go atretic. So we start out with, what is it, uh, 10 million? I know you just had-
- PAPeter Attia
I know. I just talked about this with Paula. The numbers are sort of staggering how much attrition there is between birth and, uh-
- CHCarole Hooven
So and then you end up, at birth, you have one million, and, or something like that. Okay, I'm not-
- PAPeter Attia
It may be a million-
- CHCarole Hooven
I don't think I have the numbers
- PAPeter Attia
... to a hundred thousand to-
- CHCarole Hooven
Right.
- PAPeter Attia
Yeah, yeah.
- CHCarole Hooven
Um, but most of them just die.
- PAPeter Attia
Yep.
- CHCarole Hooven
So maybe there's some selection process there. There's a overproduction, and then because for females, there's so much that goes into the production of each egg and time and energy, and each egg, um, that you produce is gonna limit your ability. If it takes a long time, that means you can only have, like, 8 or 10 or however many kids over a lifetime. Um, so they're very valuable. So we're talking about testes and sperm being, uh, testes sort of being not so well protected, but the eggs are extraordinarily well protected if they're, um, made early and then just stored-
- PAPeter Attia
Yeah
- CHCarole Hooven
... I, I think. And, uh, th- they resume meiosis, of course, when, when they are ovulated. So maybe there's this store, and then there's a selection process that goes on throughout life.
- 55:04 – 1:09:10
How evolutionary biology shapes sex differences in play, aggression, & conflict resolution
- CHCarole Hooven
male mammals that have to compete for status and, uh, operate in a dominance hierarchy, there's a, a, a lot of male mammals have dominance hierarchies wh- which tend to function to reduce aggression overall, because instead of duking it out every time there's a fertile female or a delicious piece of fruit in a tree, you just signal, "I'm not gonna take your fruit. I'm subordinate to you," uh, so you can get along kind of as a group. Yes, there's, there's infighting just like humans have, but humans have dominance hierarchies also. And if you don't learn how to compete physically with other males as a kid, this has been shown in, in non-human animals, and there's some evidence for this in humans, that, uh, you have more trouble... Sorry, it just occurred to me that this is obviously happening with social media. People are using their iPhones to compete instead of getting out in the yard and play-fighting or fighting with other boys. That's actually healthy because it ends up reducing aggression. It, it helps especially young boys and young men learn their place in the hierarchy, what they're capable of physically, how to be threatening and when to be threatening, uh, when to signal that they're submitting. You know, all of that happens, and it's fun, so they're driven to do it because it's adaptive for them evolutionarily. So I just wanted to throw that in. And females tend to have more nurturing play. I had three older brothers. I was climbing trees. I was wrestling with them. But the girls almost never play by choice just, uh, with each other. Like, they don't have a play date where they just tackling each o- they're tackling each other. My son is 16 now. He's still doing it, and he's six feet, and his friends are like, one of them is like 6'2", and it makes me very, very nervous, um, 'cause they can really hurt each other now.
- PAPeter Attia
Yeah.
- CHCarole Hooven
But yeah, they're still doing it, but...
- PAPeter Attia
Yeah, it's, it's, it's so-- it's such a beautiful thing to watch if you, if you just stop judging it for a moment and just-
- CHCarole Hooven
[laughs] Yeah
- PAPeter Attia
... ask yourself the why question.
- CHCarole Hooven
Yeah.
- PAPeter Attia
Like, what is driving this behavior, right?
- CHCarole Hooven
Yeah.
- PAPeter Attia
So again, for whatever reasons that are tragic, this has become a political discussion, but it's really not. It's simply a discussion of biology, and it's endlessly fascinating, right? Like, why is it that when I walk into the pantry and I see a candy bar versus a cheese stick or something, I want to eat the candy bar? Well, that's evolution. Like, I can't-- I, I can make a choice not to do it, but it would be silly for me not to appreciate how much my brain looks at the candy bar and sees the sweetness, the energy density, the fat, the sugar, and it's like, "Yeah, that's what I want."
- CHCarole Hooven
Yeah.
- PAPeter Attia
Versus like, you know, whatever, pick, pick the bland, healthier option. And similarly, when we watch kids play, um, I find it very interesting. I wasn't obviously aware of half of what you're saying, but this idea that, um, if you let boys kind of duke it out the way we all did, um, that ultimately it settles them down. Uh, y- again, 'cause it's probably too soon to tell what the results are of the natural experiment where kids play less. I mean, uh, uh, y- we-- there's certainly no shortage of discussion about what happens when kids are-- all the anxiety and things that come from endless social media. But this is kind of a deeper, uh, and more interesting question, which is what does it teach us about aggression, uh, or lack thereof? And, um, I'm, I'm curious. Have, have people been studying that as closely as the, as they've been studying the effects of social media on anxiety-
- CHCarole Hooven
Yeah, I don't-
- PAPeter Attia
... and some of these other things?
- CHCarole Hooven
I know that there are-- I'm not sure, um, what the current literature is on how social media is affecting play other than it's not happening as much-
- PAPeter Attia
Yeah
- CHCarole Hooven
... which I think is obviously bad. Uh, you're out there, you're being physical, you're learning about your body, you're, uh, developing relationships with other boys in particular that are trusting, but in- can involve physical aggression.
- PAPeter Attia
Mm-hmm.
- CHCarole Hooven
And you mentioned something about there, about, um, wanting to have-- What did you say? The chocolate bar? What was it?
- PAPeter Attia
Yeah, yeah, just, uh-
- CHCarole Hooven
Okay. Yeah
- PAPeter Attia
... like, your knee-jerk reaction is to always-
- CHCarole Hooven
Yeah
- PAPeter Attia
... eat something that's sweeter, more calorie dense.
- CHCarole Hooven
Yes.
- PAPeter Attia
You know, it's, it's-
- CHCarole Hooven
Okay, so that's a mis- we have a mismatch. We're designed to be motivated to seek out these foods, and we have to expend energy to get high-calorie foods. Say like we would have maybe gotten honey, and that would have been super rewarding, and we only would have had a little bit, and then we would have ran around-
- PAPeter Attia
Right
- CHCarole Hooven
... and spent those calories, and now we have, you know, you can just get your chocolate bar. So that's a mismatch situation that's maladaptive. And what's interesting is that we've figured out what to do to some degree with the male, uh, f- any women watching this who are super competitive and aggressive, that's a thing too. It's not that women are not this way. They certainly are, and I see more and more examples on my iPhone from like basketball games and stuff recently. Um, but they're not-- they tend to be less physically competitive than men.
- PAPeter Attia
On average.
- 1:09:10 – 1:13:12
Why males commit disproportionately more violent crime
- CHCarole Hooven
behavior.
- PAPeter Attia
So let's talk a little bit about the pathology, though. You just alluded to it, right? There aren't too many female murderers and rapists, and the, the disproportionate representation of men in violent crime is, you know, you don't need statistics to understand that.
- CHCarole Hooven
Right. But we definitely do have the statistics, like 95%-
- PAPeter Attia
Yeah, yeah
- CHCarole Hooven
... of murderers everywhere are-
- PAPeter Attia
Okay
- CHCarole Hooven
... male, and obviously sexual assault is-
- PAPeter Attia
Right
- CHCarole Hooven
... you know, 98% or something.
- PAPeter Attia
So what, what do, what role does testosterone play in that?
- CHCarole Hooven
So here again, I think just like with play, uh, people aren't gonna like this, but I wanna make sure I-- So I wanna make sure I s- I say it clearly. I do think that the difference, this broad pattern, is similar to what we see in non-human animals, where the males are much more likely to kill each other than the females. There's many more violent or aggressive, physically aggressive interactions. So we have the same, like if you look at both of us, we have different bodies. You are bigger and stronger. I started lifting weights because of you a year ago, so I'm, I'm getting there, but I'll never get to where you are. Also, I'm older. But, um, so physically, m- men are developed for competition, for m- essentially male-male competition for mates. This plays out in this destructive way in, in society. Um, and so I'm, I, I believe that the ultimate reason for the difference is testosterone. Uh, however, the, uh, crime, say, the murder rates in Canada, m- men are committing, you know, fewer murders in Canada than they are in the US-
- PAPeter Attia
Right. We can't attribute that-
- CHCarole Hooven
And more in-
- PAPeter Attia
... to testosterone levels.
- CHCarole Hooven
So that's not because of differences in testosterone level.
- PAPeter Attia
Yeah.
- CHCarole Hooven
It is because socialization and culture, religion, the laws, uh, you know, all have a huge impact on what the values are in a, any particular society, what is tolerated, what is encouraged. Some societies basically allow men to beat and rape their wives, right? So it's h- so you have higher rates of those male behaviors.
- PAPeter Attia
Yep.
- CHCarole Hooven
Where it's not tolerated, and the culture is totally different, you have lower rates of those behaviors. But everywhere, you're, you will have the sex difference with all of these behaviors higher in men. Uh, so I'm glad you asked this because the re- I think the main reason people don't like biological explanations for sex differences is, is because they misinterpret, uh, a tendency or a predisposition for a behavior or a, um, or a biological explanation as suggesting that it's impossible to change behavior. It's not. Uh, you know, that there's no variation across the sexes in behavior. There is. And just because there might be a biological explanation or even a, a genetic explanation, uh, the important thing to remember is that we develop within an environment. Every, you know, it's gene-environment interactions. We develop within a society, and how we develop and even how our hormones, say, respond to different kinds of interactions is impacted by the social system and, and by the ecology and everything else. So it's complicated. Um, but yeah, I think that the re- the ultimate reason is, is because of gen- the genetic difference, which is the Y chromosome and the hormones that it, hormonal differences that it leads to. And I, you know, we haven't talked
- 1:13:12 – 1:15:59
Why females evolved different behavioral strategies
- CHCarole Hooven
about female behavior, but of course, nurturing, if you're going to be growing and producing and holding and feeding and caring for a baby, and you're the one who absolutely has to do it, and that's the female. Of course, we get help from men, um, and sometimes men even take over as the, uh, primary caregivers, which is extremely unusual in animals, uh, in mammals. But So men are capable of all of that nurturing if the society values it, 'cause some societies don't value that, and then they're still capable, but they're not apt to do that. Uh, but so for females, it just doesn't pay reproductively, uh, in general, to be super aggressive. We need our bodies to be healthy, and we have to live a long life, so the longer our lives, the longer our reproductive output. Men can live short, uh, you know, die young and-
- PAPeter Attia
Right, because they can seed many more times
- CHCarole Hooven
... and have great reproductive success. Yes, if they take risks, and physical risks, and that just doesn't have the same payoff for females. There are some, uh, primates for instance, where the females are, you know, relatively aggressive, but it's almost never to the same extent, um, as males.
- PAPeter Attia
It's so interesting when you think about how as humans, right, like we, we hold ourselves to a higher standard than we would hold animals, right?
- CHCarole Hooven
[laughs]
- PAPeter Attia
And, and, and, uh, look, but I'll give you, I'll give you a very concrete-
- CHCarole Hooven
Yeah
- PAPeter Attia
... example, okay? So if we go back in time 500 years, first of all, neither of us would be alive, so let's, uh, forget that part of the discussion.
- CHCarole Hooven
[laughs]
- PAPeter Attia
But let's just say 500 years ago, if you had a male that was 25 years old, he would readily reproduce with a 14-year-old female.
- CHCarole Hooven
Yeah.
- PAPeter Attia
Right? That would be completely normal and evolutionary, evolutionarily wise. But we've made a decision, at least in our society, that that's unacceptable, and I think most people think that that's a good decision, right?
- CHCarole Hooven
Yeah.
- PAPeter Attia
So that's an example of we have made a societal norm-
- CHCarole Hooven
Right
- PAPeter Attia
... that says it's unacceptable for a 14-year-old girl to be reproducing, um, certainly at the hands of an older man. So if she gets pregnant from her 14-year-old boyfriend, we, that's a different discussion, and we can help them both out. But, but-
- CHCarole Hooven
Well, in this country anyway, yeah
- PAPeter Attia
... my point of the story is we've made a decision-
- CHCarole Hooven
Yes
- PAPeter Attia
... that this is no longer acceptable, just as we've made a decision that a husband can't rape his wife. We have just decided that that's not, you know, maybe that was cool 200 years ago.
- CHCarole Hooven
Yeah.
- PAPeter Attia
It's not cool today.
- CHCarole Hooven
Yeah.
- PAPeter Attia
So to play the other side of some of these arguments, right, is there someone watching us who's saying,
- 1:15:59 – 1:24:45
Whether male aggression is still necessary in modern society & why the underlying biological drives persist
- PAPeter Attia
"Peter, Carole, you guys are talking about all this aggression stuff, but we're humans living in the 21st century. Like, we have to change. We have to evolve as a species." Is there a case to be made that men should be less aggressive because all of these evolutionary reasons that you described aren't as necessary? Women and men are gonna live through their evolutionary-
- CHCarole Hooven
Yeah
- PAPeter Attia
... uh, pardon me, their reproductive lives. We don't have this urgency. We don't need this competition. Again, I'm not saying I agree with that or anything, but I'm just saying, like, there, there's a steelman for the other side of this, just as in those extreme examples of we don't have sex with 14-year-olds and we don't rape our wives.
- CHCarole Hooven
So what would it take for you to not eat that chocolate?
- PAPeter Attia
Well, it's interesting, right? Food is a really tough one, isn't it? Um, it can be done. It just takes a ton of willpower. That's the truth of it.
- CHCarole Hooven
Do you think it can be... So the food is a great way to think about it. There's food and sex, uh, and aggression is for, ultimately, in a way-
- PAPeter Attia
For both
- CHCarole Hooven
... for sex.
- PAPeter Attia
Yeah, well, I mean-
- CHCarole Hooven
Or food
- PAPeter Attia
... but also for both. Yeah.
- CHCarole Hooven
But it, yes. But people will f- yes.
- PAPeter Attia
Yeah.
- CHCarole Hooven
Um, so for men more than women, aggression is certainly more about-
- PAPeter Attia
But, like, to, to play off that, I don't need to be an alpha male to get as much food as I need today. Like-
- CHCarole Hooven
But you are an alpha male, and you have a lot of food, and you have, like, y- you-
- PAPeter Attia
But I don't need to be-
- CHCarole Hooven
Certainly when you competitive-
- PAPeter Attia
You don't, we don't need to be an alpha male-
- CHCarole Hooven
You've-
- PAPeter Attia
... to get food.
- CHCarole Hooven
No, that's right.
- PAPeter Attia
That's my point.
- CHCarole Hooven
But-
- PAPeter Attia
Today I don't
- CHCarole Hooven
... so you're saying we should get rid of the drive, okay.
- PAPeter Attia
I'm not saying, I, I'm just exploring this-
- CHCarole Hooven
No, and I'm glad you are exploring
- PAPeter Attia
... this, this idea, right?
- CHCarole Hooven
Because I think, so there's physical competition, which we certainly do not need, but think about what we get from the male. So there is a sex difference in certain drives. Uh, men tend to be more sort of driven to achieve specific and more narrow goals, and, like, hyperfocused on certain goals, and to achieve via, you know, a, um, to be the top of the heap in, in one thing, like chess. I wrote some article on sex differences in chess and learned a lot about, you know, 'cause I was like, what, why are men consistently better at chess than women? And they are.
- 1:24:45 – 1:30:38
How testosterone levels naturally shift to support fatherhood & caregiving
- CHCarole Hooven
it ha- there's, it's interesting 'cause even in hunter-gatherers, there's very different traditions across hunter-gatherer societies in terms of, um, expectations for paternal involvement, and when there's high involvement, there's lower testosterone in those males. That applies to humans and non-
- PAPeter Attia
Sorry, in the, in the m- father or in the child?
- CHCarole Hooven
In the father. So for fathers to be very attentive-
- PAPeter Attia
Yes
- CHCarole Hooven
... the testosterone generally is suppressed, and that's true in m- birds-
- PAPeter Attia
Okay
- CHCarole Hooven
... where the males are contributing. If you raise it, they neglect their kids. So there is a hormonal, uh, support there for parenting, so that's something that, you know, men can do to increase their reproductive success, so I just wanna say that I think that's something that has-
- PAPeter Attia
So we don't want the lesson here to be-
- CHCarole Hooven
... is not novel
- PAPeter Attia
... if, if you're, if you're a man out there listening with low T, ignore your kids.
- CHCarole Hooven
With low T? The-
- PAPeter Attia
If your, if your T is low, you should ignore your kids to raise your T. Is that the implication?
- CHCarole Hooven
Oh, right, right. Um- It doesn't drop by that, that much.
- PAPeter Attia
All right.
- CHCarole Hooven
And what matters is that you're in an environment where you see your little kids. Like, if you're a guy and you're m- mated and you have a partner and you're around your baby and you're interacting with your baby, your T's gonna drop a little bit, and that's a good thing. And this is one of the reasons that supplementing with exogenous testosterone, there are so many different ways that testosterone, male testosterone rep- responds and inf- to and influences social dynamics, and this is one of them that's really important. You're a better, uh, dad potentially if your testosterone does drop. You're potentially a better husband and, uh, you know, more attentive to your wife and your kids. There, this is, seems, uh, I don't know that there's the experiment-
- PAPeter Attia
Do we know that there's causality here?
- CHCarole Hooven
Yeah.
- PAPeter Attia
I mean, this is a pretty bold statement.
- CHCarole Hooven
We do. I would say, yeah, we do know.
- PAPeter Attia
So what, what, by what magnitude are we talking about here?
- CHCarole Hooven
Yeah, that's a good question, and I don't, I should have had the data and I don't have the answer. But it's shown across lots of different populations in humans and non-human animals, uh, that fatherhood, first of all, mating, being in a, a pair bond, this is like, it's like what birds do when they finally-- They're very aggressive when they're setting up their territory. Their testosterone is high in, in the males. When they find the female and establish a territory with her, the testosterone tends to drop because it's not adaptive to have high testosterone all the time, and that's why animals-
- PAPeter Attia
Because it would-
- CHCarole Hooven
... have mating seasons, et cetera.
- PAPeter Attia
Sorry to interrupt.
- CHCarole Hooven
Because it's expensive metabolically.
- PAPeter Attia
Because it would make us, it would make us go out and look for other mates-
- CHCarole Hooven
Yes
- PAPeter Attia
... when we don't need to?
- CHCarole Hooven
You're aggressing and fighting for status and singing or flexing your muscles or ignoring your kids or being an asshole to your wife. I mean, all of these, um... You're also not, uh, reinforcing adaptive behaviors with a bit of a testosterone spike. Like, if you're around a, a attractive woman and you're trying to seduce her, there, there's very possibly gonna be a testosterone increase which stimulates a dopamine surge and reinforces a, a behavior if you're successful.
- PAPeter Attia
How much can that happen?
- 1:30:38 – 1:38:42
How testosterone shapes male mating strategies, & why long-term pair-bonding persists even when reproduction is no longer at stake
- CHCarole Hooven
So I, I just wanna pause here, and I wanna get back to everything else you said. Um, there are different strategies that different men can use to maximize their output, say, in a natural fertility society. One is pair up forever with one woman, mate guard her, be good to her. And I'm gonna, like, getting teary-eyed for [laughs] for some reason. Invest in her. Oh my God, I have no idea what this is about. Um, I just, just I have estrogen, and estrogen increases crying, um, which it actually does. Testosterone inhibits it, although I also put on my testosterone gel this morning. Anyway, um, [laughs] so that's one strategy. And he had to compete and have certain status to get that woman, right?
- PAPeter Attia
Mm-hmm.
- CHCarole Hooven
You want a high quality female. You wanna keep her. You can do very well reproductively from your, for your lifetime output, and you're not out on the mating market constantly being vigilant, constantly trying to take down other males, constantly fighting for status. You can have sex with a lot of women, which is what you want. You're designed to want sex with, you know, m- more partners than females are designed to want sex with. But who knows how many of them are gonna get pregnant, and who knows how many of those babies are gonna survive? But that is one strategy where if you're a high status man, you can be very successful. You can have way more than eight kids, right? But that's a high-risk strategy. A lot of men are gonna fail, and they won't have the sure thing of the one female where they can invest in her. That seems to be not a lower testosterone man strategy, but it does seem that we, we know that when the kid is young, if the guy is physically involved with the, uh, a small dependent offspring, that there will be suppression in testosterone.
- PAPeter Attia
Hmm.
- CHCarole Hooven
And that is a good thing. It doesn't mean that your muscles are, will be smaller necessarily as far as I know. I'm not sure how big the drop is, but it does facilitate potentially more contentment with that life. If you have higher testosterone, what has been shown in non-human models is that the attention to the mate and the offspring is reduced. There's more attention to status seeking, um, a, you know, aggression, getting sex from other partners, et cetera. Like, so it, I think it's worth trying to understand what the, um, exogenous testosterone, which shuts down that system, does in men who, you know, I think there are potentially some very important behavioral and social effects that people don't think about because they're so psyched to get jacked and have more social status and have the dopamine hit. You know, it feels good. Um, I, I don't know. Uh, it's, I think it's worth looking into.
- PAPeter Attia
I mean, there's so much to unpack there, and it's, it's, it's such a, again, these evolutionary discussions are so interesting because I, I have to imagine that most guys who have chosen the path on your, uh, right, uh-
- CHCarole Hooven
[laughs]
- PAPeter Attia
... which is I'm gonna have as many partners as possible, are not doing that because of reproductive fitness.
- CHCarole Hooven
Oh, no, of course not.
- PAPeter Attia
They are often choosing not to have kids.
- CHCarole Hooven
That's right.
- PAPeter Attia
So I, I, how do we reconcile that, right? From an evolutionary perspective, I get it. The desire to have as many partners as possible increases your probability of su-
- CHCarole Hooven
Or even just, you know, serial monogamy, where you're in-
- PAPeter Attia
Yeah
- CHCarole Hooven
... a relationship, and then you sort of move on, or you divorce your wife and get a younger partner and then divorce your wife again and get a younger partner.
- PAPeter Attia
And is that rooted in evolution of reproduction, or is that rooted in the evolution of status in a way that is distinct from reproduction, you think?
- CHCarole Hooven
So do you mean, so I don't think status is distinct from reproduction. Do you mean psychologically-
- PAPeter Attia
Yes
- CHCarole Hooven
... what is the driver?
- PAPeter Attia
Yes.
- CHCarole Hooven
It's not reproduction. It's sex. It is sex.
- PAPeter Attia
Which is interesting. So this is the first time we're basically talking about sex independent of reproduction.
- CHCarole Hooven
Yeah. I, it's, um, ultimately, I think it is, uh, of course, we have love, and we have relationships and all of that, but that is for reproduction. That whole love thing is just to get the gene, the kids' genes into the, your genes into the next generation via the, the kid. And the love of the wife is to ha- is to ensure [laughs] that, you know, maximize the chances of that happening. So-
- PAPeter Attia
But are we, are we, is there any other species that does what we do as humans, which is, so you and your husband have a 16-year-old and-
- CHCarole Hooven
That's it.
- PAPeter Attia
Okay. So in two years or three years, when he's off in college-
- CHCarole Hooven
Oh, boohoo. Don't talk about it
- PAPeter Attia
... I know, I know, it's terrible, right? So, um, you guys will have done your job as parents, but, and-
- CHCarole Hooven
No, we're gonna keep doing it until we die.
- PAPeter Attia
No, no, no, okay, but, okay, but my point is-
- 1:38:42 – 1:49:50
The distinct roles of estrogen in male development, mood, libido, & muscle
- PAPeter Attia
You mentioned, so again, going back to kind of testosterone and estrogen, I wanna talk a little bit about estrogen now. So, um, obviously estrogen is a very important hormone for men and women. It's appreciated more, I think, in women than men. But, um, you know, to cite one study that I've talked about many times in the past, it, it's about a 13-year-old study that took men, uh, took a large group of men, chemically castrated them all, and then re- you know, made them replete with different doses of testosterone-
- CHCarole Hooven
Yeah
- PAPeter Attia
... with and without anastrozole. So-
- CHCarole Hooven
Oh, right
- PAPeter Attia
... so this study basically gave men ver- you know, I think there were five groups of testosterone and with and without anastrozole. So for folks listening, anastrozole would inhibit the conversion of testosterone to estradiol. So you bas-
- CHCarole Hooven
So it just inhibits aromatase.
- PAPeter Attia
That's right.
- CHCarole Hooven
Yeah.
- PAPeter Attia
It's an aromatase inhibitor. So you have, you know, from low to high, five levels of T with and without estrogen.
- CHCarole Hooven
Okay.
- PAPeter Attia
So it's a pretty elegant study, right?
- CHCarole Hooven
Way to know who, do you know who the-
- PAPeter Attia
It was in The New England Journal of Medicine.
- CHCarole Hooven
Okay.
- PAPeter Attia
I don't remember who, who published it. We'll link to it in the show notes.
- CHCarole Hooven
Okay, great.
- PAPeter Attia
Now, um, the question was, what did these 10 groups, how did they differ, um, with respect to, uh, body composition, uh, mood, affect-
- CHCarole Hooven
Bone density
- PAPeter Attia
... sexual desire, all these sorts of things. I don't remember if bone density was studied.
- CHCarole Hooven
Okay.
- PAPeter Attia
Um, it might not have been a long enough study. I, I, d- it's been so long since I've looked at it.
- CHCarole Hooven
Okay.
- PAPeter Attia
But here was the big takeaway. The, the TLDR was by far the best producing outcome was the highest T with high estrogen.
- CHCarole Hooven
Producing outcome for?
- PAPeter Attia
Everything. For body composition-
- CHCarole Hooven
Okay
- PAPeter Attia
... mood, you name it. So in other-- The, the, the, the learning to me, it wasn't surprising that higher testosterone was better than lower testosterone for all the metrics that were measured. The surprising insight at the time, again, is we now I think understand this much more, but for me at the time, the surprising insight was more estrogen was better than less for men.
- CHCarole Hooven
Mm-hmm.
- PAPeter Attia
Not just with respect to how they felt, but even body composition. And this was a wake-up call because I think there were a lot of doctors out there who were prescribing aromatase inhibitors to keep estrogen as low as possible in men. You know?
- CHCarole Hooven
In men who were...
- 1:49:50 – 2:02:44
How evolution, health, lifestyle, & androgen receptor biology shape modern testosterone replacement therapy (TRT)
- PAPeter Attia
us about the role of testosterone replacement therapy in both men and women, right? So let's go back-
- CHCarole Hooven
Yeah
- PAPeter Attia
... to something you said some time ago. So if we didn't muck around with nature, men would experience a pretty steady decline in testosterone from puberty on down. It never really has-
- CHCarole Hooven
In Western populations-
- PAPeter Attia
Oh
- CHCarole Hooven
... 'cause we don't, hunter-gatherers tend not to have that.
- PAPeter Attia
Oh, okay. Well, say more about that.
- CHCarole Hooven
Yeah. Um, well, they start out with lower testosterone because, again, testosterone is expe- high testosterone is expensive to maintain. Most animals keep it low and only raise it when females are fertile, and they need to compete. So that's why they're-
- PAPeter Attia
So that's the rut. Like, we're, we're-
- CHCarole Hooven
That's the rut
- PAPeter Attia
... animals, basically.
- CHCarole Hooven
Like, like if the red deer, you know-
- PAPeter Attia
Yeah, yeah, yeah
- CHCarole Hooven
... grow, their, their testicles grow. They grow weapons on their head. They become horny. They become aggressive when the females are fertile. If the females aren't fertile, all that stuff goes away, testosterone drops. Okay, so humans are also designed to keep testosterone low, which is why if there's a situation, a competitive situation, say, testosterone might go up, but generally it's gonna be kept low when it can be. But we are over-nourished in Western populations. We don't have to worry. We have enough calories to run our immune system and to do everything else we need to do. We have the luxury of being able to elevate testosterone over what it would be naturally.
- PAPeter Attia
But, but-
- CHCarole Hooven
So, yeah
- PAPeter Attia
... s- sorry, Carole, to interrupt. In the case of the deer-
- CHCarole Hooven
Yes
- PAPeter Attia
... all of the females go through estrus at the same time.
- CHCarole Hooven
Yes.
- PAPeter Attia
So it's easier-
- CHCarole Hooven
Yes
- PAPeter Attia
... for the bucks-
- CHCarole Hooven
Yes
- PAPeter Attia
... to say, "For these nine months-
- CHCarole Hooven
Great point. Great point
- PAPeter Attia
... I don't need testosterone," because all of the does-
- CHCarole Hooven
Mm-hmm
- PAPeter Attia
... are infertile, and then, bingo.
- CHCarole Hooven
Exactly.
- 2:02:44 – 2:10:32
Carole’s experience with hormone replacement therapy (HRT), & the risks associated with TRT in younger men
- CHCarole Hooven
M- I'm on progesterone, testosterone, and estrogen. I'm 59. I'm definitely, uh, and I had my ovaries out a couple years ago, and I have to say, I just wanna say when that happened, I was 57, so I was already in menopause pretty much, and, uh, everything changed after that. Like, it made a huge difference. My hair started falling out. My sex drive plummeted.
- PAPeter Attia
Sorry, just to be clear, you were on hormone replacement therapy-
- CHCarole Hooven
No, I was not
- PAPeter Attia
... prior to?
- CHCarole Hooven
No.
- PAPeter Attia
No. Okay.
- CHCarole Hooven
And I had my, I just was, I just wanna throw that out there because even, uh, I'm supposed to be an expert in hormones and I had my ovaries out at 57, and it was a huge, had a huge impact
- PAPeter Attia
Even though you were already in menopause?
- CHCarole Hooven
Yeah, I mean, I guess I wasn't f- we found out I wasn't actually f- I had some fresh corpus luteum in my ovaries, [laughs] so they said I wasn't actually in menopause. But, uh, yeah, it's just amazing. Even when they're pumping out low levels of hormones, I think-
- PAPeter Attia
They're still doing something
- CHCarole Hooven
... they're still pretty impactful. So yeah, I'm on-
- PAPeter Attia
So why did you decide to only go on hormone replacement therapy at the age of 57 when presumably you believed you were, uh, in menopause prior and didn't go on HRT?
- CHCarole Hooven
That's a good question. I guess 'cause I felt fine, and it wasn't until-
- PAPeter Attia
It was gradual
- CHCarole Hooven
It was gradual.
- PAPeter Attia
Yeah.
- CHCarole Hooven
Yeah, and, and, but that's a great question. Um, I think especially the, I, I, because of you, I started lifting weights a year ago. It total, totally-
- PAPeter Attia
You look like y- you look like you've been at it for years.
- CHCarole Hooven
Oh, thank you. No, I was just a runner and, you know, Peloton and biker and all that, and, uh, it's made a huge difference, I just wanna say, to, to, um, get into lifting. Now I'm addicted to that, and now I, now I have a back injury, um, which you'll have to help me with later. So [laughs] um, I think the testosterone must be helping-
- PAPeter Attia
Yeah
- CHCarole Hooven
... there in terms of my, like, really getting into the workouts and how much I can lift potentially. Um, I can't even remember what you asked me now, but oh, I guess I'm saying I myself am, am on these hormones.
- PAPeter Attia
And it sounds like you feel better as a result of it.
- CHCarole Hooven
Yeah, I think so. I think I feel better, but I definitely feel better when I'm working out and the drive to, but I, maybe I would've done that anyway. But I have no issue with people doing what they need to feel better. I just think people don't consider that especially testosterone, and I think also estrogen, these are hormones that give us signals, not about, I mean, all, about what's going on in our own bodies. Uh, like are we making eggs? Are we m- making sperm? Are we healthy? Are we sick? You know, all of that is communicated. Like, if you're sick, your, uh, those systems are suppressed, and your hormone levels are gonna be lower, which is adaptive, and it, it will help you. And, you know, and that won't happen if you're taking it all exogenously. And there's a, a lot of social signaling. Uh, so all of that goes away, but yeah, I think that's for each individual to decide. I, I do think there should be some regulation around testosterone because from what I understand, it really is addictive and also can, uh, permanently cause someone to, you know, cause someone to become infertile. Uh, that's something obviously that I don't know that people, young people in particular, really understand. So I think it's different t- uh, when people are, you know, after the age of 40 or 50.
- PAPeter Attia
Hmm.
- CHCarole Hooven
It's a different situation from someone who's young and healthy and is doing it and is getting addicted. I think at the, at younger ages, I think we should be much more careful.
- PAPeter Attia
Yeah, that's an interesting point, is, um, because as, as you know, but maybe some of the listeners don't, um, testosterone is a regulated scheduled drug, uh, hormone, whereas estrogen is not.
- CHCarole Hooven
Yeah.
- PAPeter Attia
So, um, uh, estrogen can be prescribed without any sort of DHEA scheduling. Testosterone is a schedule, I believe it's a Schedule IV. Um, and that's a real big difference.
- CHCarole Hooven
Wait, it's not DHEA scheduling.
- PAPeter Attia
Did I say DHEA instead of DE-
- 2:10:32 – 2:17:40
How Carole rebuilt after controversy: leaving academia & recommitting to scientific honesty
- CHCarole Hooven
Yeah.
- PAPeter Attia
So, um, so what are you up to right now?
- CHCarole Hooven
So I, um, am trying to finish a book proposal. I'm spending a little more time with my son, which is nice that I'm home when he gets home from school. And I have a part-time job at a DC think tank, which I'm really enjoying. Um, and I do some writing, um, and, uh, yeah, that's about... I mean, I have other things that I do, but-
- PAPeter Attia
Yeah
- CHCarole Hooven
... those are the relevant things.
- PAPeter Attia
So I don't want to go too far down the rabbit hole of what many people, if they Google you, are going to learn about the horrific experiences you had, but how long ago was all of that? That was about three years ago?
- CHCarole Hooven
So that was tw- happened, it started in twenty twenty-one, yeah.
- PAPeter Attia
So four years ago. So how, how has this experience been for you? You're four years on the other side of, I think, what any reasonable person would, would look at and say is just a, a complete and total injustice. Uh-
- CHCarole Hooven
Thank you
- PAPeter Attia
... a, a lot of incredibly cowardly people that I'm sure at one point you felt were friends and colleagues that, you know, completely sat by silently as a, as a, as a, as a minority mob went after you. Um, how are, how are you recovering from that experience?
- CHCarole Hooven
It's been really difficult because, uh, I was just reading my acknowledgments in my, um, book on testosterone, and I wrote, you know, "I have a great job. I have the privilege of interacting with these amazing young people." And it's, uh, it was teaching and advising undergraduates, uh, is hard. You know, it's hard. I, I teach about some really controversial and detailed and intricate, uh, topics, and I love that. I love putting in the effort and feeling the reward, you know, every day. And I loved have-- the relationships and changing people's lives and having them change mine. And it's a big, you know, that's work that is challenging and so deeply rewarding, and it helps to provide a sense of meaning in life and a sense of accomplishment and all these things. So not having that, um, is hard, and it's hard coping with the reason I don't have that and all the people and the institution I trusted and gave so much to and feel, uh, yeah, I feel that I was treated pretty horrifically. So it's hard. It's a transition. I know that it's a transition. I've had transitions before, uh, but this is a big one. I thought I'd be in that job forever. Um, h- but what it has done for me is made me much more committed to doing something like what you do, which is why I'm a hu- part of why I'm a huge fan of yours, and I'll probably start to cry again. Um, and I think it's very rare that there, that people get so into the scientific weeds with... I don't detect any bias on your part. I detect your very open and honest struggle to understand the evidence and to talk about the evidence and where it points, and that's what I've always tried to do. And I think it is so important, not just for science, but for people to be able to communicate with each other and share facts. Maybe we disagree about the implications of the facts, uh, but it's so important to take ideology and bias out of our understanding of reality. Reality's there whether we like it or not. It's always to our benefit to understand it and to try to figure out then to use, like, democratic processes to figure out what to do with reality or, or how to improve human health or whatever the issue is. So I guess that experience has just made me much more committed to doing that and to advocate for that, um, which isn't always easy. And it, you know, some of the things I said today are c- controversial, but, you know, I'd love for, to hear what, um, if people disagree, why, and then that's how we learn is by having our views and interpretation of evidence challenged.
- PAPeter Attia
So given how, in many ways, successful you were as a professor, how much your undergraduate students loved you, um, it's certainly one vehicle through which you can communicate this passion. Do you see yourself going back to that situation? Do you see yourself winding up back at a different university one day, or do you feel like, you know, the scars are sufficient that you don't feel like being in that arena again?
- CHCarole Hooven
So yeah, we didn't say what happened. I'll just say that I wrote a, a book, uh- T: The Story of Testosterone, The Hormone that Dominates and Divides Us. And I went on Fox News and, um, said that there are two sexes, male and female, and someone who was representing themselves as, uh, speaking on behalf of Harvard and my department accused me of transphobia. And then there was, there were other bad things that happened, and it resulted in me feeling I had no choice but to leave my job that I'd been in for over 20 years and, and loved. Um, and now I forgot your question. [laughs] So.
- PAPeter Attia
Would you see yourself back?
- CHCarole Hooven
Yeah.
- PAPeter Attia
Yeah.
- CHCarole Hooven
So no, because I'm so tra- I was traumatized. I was in shock. I could not believe how people were behaving, and I learned a lot, and one of the things I learned is that I was way too trusting. And whatever I do, I wanna throw myself into it, and I threw myself into that job, and that's why it hurt so much, because that was me. That was, like, all of me. I mean, I kept some of me, uh, for, for other parts of my life, but I really threw myself into it, and they-- everyone who worked with me knows that. And so it feels way too risky. I don't-- I won't trust an institution like that again. Um, or I don't know. I'll have trouble... Yeah, academia for me right now, not a fan. [laughs] So.
- PAPeter Attia
I think I'm sure a lot of people can relate to that because anybody who's put every bit of themselves, ev- uh, take an example like your first love, right? The first person you fall in love with.
- CHCarole Hooven
Yeah.
- PAPeter Attia
If they break your heart-
- CHCarole Hooven
Oh, yep
- PAPeter Attia
... you're gonna sit there and say, "That wasn't worth it. Like, I'm, I'm not doing that again."
- CHCarole Hooven
Mm-hmm. Mm-hmm.
- PAPeter Attia
The, the, the bliss of that experience wasn't worth the pain I'm experiencing today. Um, and I'm not gonna sit here and suggest that you have to do it again because of, you know, look, look at all the students you were able to help because there's other ways to do it, and you're obviously writing another book. And so, um, you know, the truth of the matter is being on a podcast probably reaches more people than you would reach in ten years of teaching.
- 2:17:40 – 2:25:41
Carole’s next book: examining masculinity, cultural narratives, & the cost of denying biological sex differences
- CHCarole Hooven
Right.
- PAPeter Attia
Um, what is, uh, what is your next book about? If you're-- Are you comfortable talking about what the subject is?
- CHCarole Hooven
Oh, totally. I'm really excited. It's about what's happening with masculinity, and I'm really interested in the cultural narrative. Uh, here's where I also cry, and that's how I knew I needed to write a book because why am I crying about masculinity and men being denigrated? Uh, which I get very upset about that. Uh, and I wanted to really understand what was happening culturally, why we are in a place where masculinity is, um, not valued, and also to explore the interaction between biology and genes and hormones and what's happening culturally. Why is it that these cultural changes that we've had are affecting men in the ways that are different from how they're affecting women, like economic changes, um, uh, you know, men are falling behind in education, for instance. And why is-- why-- what's happening in schools, and why are schools maybe less hospitable to typical male ways of behaving than typical females? So I really wanna dive into that intersection, um, and to explore some of the questions that we-- you were asking today about aggression and sort of men's-- w-we were talking about men's need, um, to compete and how it's different from women and how that plays out socially. So I wanna explore those issues really with an eye to understanding what's called the masculinity crisis and what I think has been, um, th-that there's a kind of backlash going on right now, which I think is interesting, um, in that men and their needs and their right to be masculine, I think has been under attack. And now I think there's a bit of, yeah, uh, some men are feeling freer to be more masculine, I would say today. What I want to explore is the denial of sex differences-
- PAPeter Attia
Yes
- CHCarole Hooven
... and how that plays out socially. Because if you believe that men and women are equally interested in engineering, then you don't believe in sex differences. You don't believe there are you-- important, meaningful differences between the sexes that play out in society-
- PAPeter Attia
Yeah
- CHCarole Hooven
... that are not all the result of the patriarchy, say. Certainly, there are social influences i- and, and that all matters, but there's this denial of that, of, of real differences, um, that we need to grapple with socially. And if it's-- if you, um, believe that all the differences are the result of society, then you're justified-
- PAPeter Attia
Yes
- CHCarole Hooven
... in, uh-
- PAPeter Attia
Yeah
- CHCarole Hooven
... say, po- potentially you're more justified in trying to create eq-equal outcomes, right? But if you deny biological differences, um, y- then you have more of a reason to do that. But if you appreciate that they're real and that we have to grapple with them socially, then it's gonna be more complicated, right?
- PAPeter Attia
Yeah. I, I, I mean, I, I completely agree. I mean, I, I joke about this with my wife all the time, right? Like, the, the reaction she has to a naturally aspirated V8 engine screaming at ten thousand RPM versus my reaction-
- CHCarole Hooven
So you go towards, she goes away, basically
- PAPeter Attia
... I mean, like, it's the greatest sound I've ever heard.
- CHCarole Hooven
Right.
- PAPeter Attia
And she is like, "What is that awful noise?"
- CHCarole Hooven
[laughs] Right.
- PAPeter Attia
And there's no socialization-
- CHCarole Hooven
Right
- PAPeter Attia
... that creates that difference. Like, on average, 'cause we only, we can only talk in averages here, men are way more hardwired to love that sound. Like-
- CHCarole Hooven
Yeah
- PAPeter Attia
... and, and I-- there are incredible-
- CHCarole Hooven
Could it be interested in cars?
- PAPeter Attia
Sure, sure. But there are incredible-
- CHCarole Hooven
And the mechanics of cars
- PAPeter Attia
... YouTube videos where you can literally listen to every engine.
- CHCarole Hooven
Oh, and it's like ASMR for you?
- PAPeter Attia
Yep. The V8 and V10 naturally aspirated engines screaming is the greatest sound I've ever-
- CHCarole Hooven
Wait, I don't know what, uh, naturally aspirated
- PAPeter Attia
Oh, just, it ju- just mean it's, that you don't have forced induction of air-
Episode duration: 2:25:41
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