Deena Emera Episode === [00:00:00] You mentioned the grandmother hypothesis. So this is one of the well-known, best known theories on why we go through menopause. It's actually not a hypothesis on why we go through menopause. It's really a hypothesis about why humans evolved to live longer. And so what do I mean by that? What's unique in humans and killer whales is that we live so much longer, past, the age at which we run out of eggs. So menopause itself is not that surprising in any species. Deena: Running out of eggs is exactly what you'd expect. Deena: What's unusual is that, we live so long beyond, [00:01:00] Mellisa: Hey, welcome to threshold wisdom previously known as this is aging. And you are in for a treat today. I have got an evolutionary geneticist on the show and we are going to talk about the mysteries of the female body from a perspective and an angle that might be totally new. It's definitely new for me. And I learned so much in this episode. I don't think there's any need to say anything else. So let's just get into it. Mellisa: Melissa here, and I've got Deena Mellisa: Emera here on the show. Mellisa: Deena Mellisa: is an evolutionary geneticist, an author and a teacher, and she earned her bachelor's degree from uc, Berkeley. Mellisa: She's Mellisa: got a Mellisa: master's from NYU and a PhD from Yale. Mellisa: She currently Mellisa: serves as a scientist and writer and residence at the Buck Institute, Center for reproductive longevity and equality.[00:02:00] Mellisa: And one Mellisa: of the Mellisa: reasons I'm most excited to have Deena on the show is because she recently published a book called A Brief History of the Female Body, which is Mellisa: really Mellisa: drawing on Mellisa: her expertise as a biologist, and also it turns out a mother of four. Mellisa: I'm Mellisa: so excited to chat with you, Deena, and learn more about the mysteries of the female body. Mellisa: I think that some of the episodes that we have done on the show that have Mellisa: Approach the conversation, the very necessary conversation about hormones and what happens in midlife Mellisa: do leave a little bit to be desired in the sense of like, why is this, ha, why is this stuff happening in our bodies to begin with? Mellisa: And should we really mess with it? Mellisa: So welcome. Mellisa: you. wanna Tell me just a little bit more about you before we dive in? Deena: in. Yes, thank you. It's such a pleasure to be here. So I think you hit all the important points. I'm a scientist. I have spent a lot of my career studying [00:03:00] female bodies, female reproduction. Deena: My PhD was on the evolution of pregnancy, so I studied. I'm very interested as a biologist in sort of big transitions during evolution. So, pregnancy's a perfect one 'cause mammals used to lay eggs. So how do we go from. Laying eggs to growing our babies inside our bodies. So these are the sorts of questions that I'm really interested in. Deena: I studied periods, and for everything that I, investigate. I'm interested in both the how and the why. So, Deena: I'm a geneticist, so I'm really interested in the how, like how did, what were the changes in DNA that require that, sorry. That led to these big changes in bodies. Deena: But of course when you're studying the how, you're also very interested in the why. Like, why did we start, why did mammals start growing babies inside their bodies instead of continue to lay eggs? So, those are the types of questions I'm interested in. [00:04:00] And I've done lots of different things over the course of my career, but I'm sort of back to the female reproductive system studying. Deena: Menopause and the lack of menopause in mammals. Mellisa: Yeah. We're definitely gonna talk about that because that is so interesting to me. And it again, like I said, has come up Mellisa: in other conversations and I think it's I Mellisa: think Mellisa: there's just a lot of Mellisa: uncertainty and mystery around Mellisa: around Mellisa: what Mellisa: is Mellisa: really going on in the Mellisa: female body. What Mellisa: and if we should be Mellisa: intervening Mellisa: in some of these ways that are available. Mellisa: to Us nowadays. Mellisa: So, Mellisa: I Mellisa: wanna start with asking you, Mellisa: because, Mellisa: 'cause, ' Mellisa: some of your most recent things that I've seen you post about on social media have actually had to do with aging. So let's start there because Mellisa: that Mellisa: is one of the, the broader concepts that we're talking about here on the show. Mellisa: Can I Mellisa: ask you first what your Mellisa: current Mellisa: relationship to aging is like? Mellisa: Just Mellisa: your Mellisa: own experience? Mellisa: of it. Yeah, that's a great question. So I'm in my mid [00:05:00] forties. I think, as many women in their mid forties are experiencing or have experienced, that's perimenopause. So, for me how that is manifesting is anxiety. Deena: You mentioned I have four kids, so you know, I'll. Set out to do a task that I've done a million times, like make everyone dinner. I think because I, my hormones are, , behaving in a different way than they used to. One of the side effects of that is, feeling very anxious or overwhelmed about like a very trivial thing. Deena: Like, I've made dinner so many times, so I just feel this. How am I ever gonna do this, and I have to calm myself down and break it down into steps. So for me, , I'm not having any of the classical symptoms of perimenopause and menopause. Like, I haven't had any hot flashes or anything like that. Deena: My, this, maybe this is too much [00:06:00] information. My, my periods are very regular still, but they have definitely shortened, which is one of the early, of perimenopause is that your cycles do get shorter. But yeah, the anxiety and a little bit of depression again, completely new. Deena: I've never had, I've never experienced those, symptoms I've never had those, , feelings before. And I think that's, a big challenge of women now. At, in their forties because a lot of women are having kids later. , you've got all the responsibilities, of raising younger kids and older kids. Deena: My kids span, nine and a half years. So I've got a teenager, but I've also got a 5-year-old. Mellisa: Yeah. I'm in the same boat. Deena: yeah. So, we've got, the. Challenges of mothering young kids. But we're doing it at a time, perhaps later than our moms or grandmothers, were doing it. And so our hormones are starting to fluctuate. Deena: We're starting to have these, new [00:07:00] symptoms. Our parents are older, so it's just you're s. Just slammed from all directions. Many women who are working, it might be a critical part of, their career where their responsibilities have ramped up. It's a hard time. Deena: I'm navigating it fine. I have a very supportive partner. It's hard for sure. Mellisa: I Mellisa: think Mellisa: you're Mellisa: absolutely right that Mellisa: now Mellisa: more than ever. Mellisa: we Mellisa: have so much on our plates, and Mellisa: you've Mellisa: probably heard the term, the sandwich generation, where Mellisa: you Mellisa: know, Mellisa: at, that time of life where you're caring for kids, you might also be caring for aging parents. Mellisa: And you've got Mellisa: a career that Mellisa: is in an important, like you said, critical Mellisa: stage Mellisa: of its maturation. And I do think that Mellisa: being in Mellisa: our forties and still having young kids is probably physiologically not Mellisa: ideal. Because we're. We are having changes in energy levels and all of that kind of stuff. Mellisa: We did an [00:08:00] episode Mellisa: With Mellisa: the Mellisa: women at Wise and Well Mellisa: about Mellisa: midlife hormones and They actually said that the two Mellisa: first Mellisa: things to Mellisa: aware of Mellisa: that will happen in menopause are, or sorry, in perimenopause, Mellisa: are Mellisa: mood changes Mellisa: and Mellisa: sleep disturbances. Mellisa: And that was Mellisa: really Mellisa: educational for Mellisa: me. because I think yes, we do tend to just hear about Mellisa: the Mellisa: really, Mellisa: the things that we hear about are Mellisa: hot Mellisa: flashes. Mellisa: And Mellisa: The loss of menstruation. And ultimately some people may not experience hot flashes or Mellisa: may not until Mellisa: later in the Mellisa: journey. And it's those early things that can actually be so disruptive. But we're not. Mellisa: even really paying attention to them. Deena: Or we've noticed them, but we're blaming it on something else. Deena: The sleep, we're blaming it on stress. Deena: I will say on the sleep, I didn't mention that was one of the things I was experience experiencing. But I mention it [00:09:00] now because I cut out caffeine and that has made a dramatic difference in my ability to sleep at night. And I made the mistake yesterday. Just, this is fresh in my mind. Deena: Of having a cup. I do drink one cup of black tea, like first thing when I wake up. 'cause I do love caffeine. I've just switched to decaf coffee. I made the mistake though, yesterday of having a. Cup of white tea, which does have caffeine like a second cup, Mellisa: Oh, Deena: did not sleep last night. So all of that to say that I think some people are very sensitive to caffeine and I don't know of any research that suggests that this changes as we get older, but I have noticed. Deena: Extreme sensitivity to caffeine and cutting it out made a big difference. So if you are one of those women who's really suffering with sleep disruption, I would try I would try reducing coffee. I. Mellisa: Yeah, that's a great tip Mellisa: And probably Mellisa: not super well received because no one wants to, hear Deena: no [00:10:00] one wants to do it. No one wants to listen to me when I say this, but, Deena: Having a cup of decaf is not quite as nice, but you still, can participate in the ritual and make the coffee and it tastes similar. Deena: So, Deena: so I'm having my cup of decaf right as we speak. Mellisa: I'm one of those very rare birds. I've never actually had a cup of coffee, so Mellisa: I don't Mellisa: even have to take your advice. Deena: Wow. Mellisa: yeah just Mellisa: Never ever got into it. Mellisa: So. Okay, so let's talk about Deena: about Mellisa: the Mellisa: recent post you did about Mellisa: the Mellisa: current Mellisa: research that is validating Mellisa: this Mellisa: theory about Mellisa: aging. Mellisa: Like why do we age and it has to do with fertility Mellisa: and the genes that are good frail, Good for fertility when we're younger, Mellisa: that then become Mellisa: more Mellisa: problematic when Mellisa: we're older. So this is very interesting to me and also Mellisa: a little bit upsetting to me. Deena: me. Mellisa: So ex Mellisa: Explain this. Mellisa: in more detail. Deena: [00:11:00] So, if you think as an evolutionary biologist, I know many people don't think this way but I'm gonna force you to do that right now for a second. Deena: Evolution is all about reproduction. So, the traits that we pass on to the next generation those get passed down because, we've had kids and, the more kids you've had the more of those traits you're gonna pass down. And of course, if. The traits are affecting how many kids you have. Deena: That's, evolution's sweet spot. That's how natural selection works, right? So nature is selecting for traits and genes that are involved in producing those traits that. Affect, you've heard of survival of the fittest. That's a little bit of a misnomer. Deena: Evolution's about survival. Natural selection is about survival, but it's really about reproduction. So [00:12:00] survival Mellisa: Reproduction is Mellisa: survival. Deena: survival. Yes. But, survival is important only because it allows you to reproduce, right? So. There are many species who reproduce in one big burst and then they die. Deena: So, nature doesn't care so much about survival. What it cares about is. Reproduction. Deena: And so one of the main hypotheses on aging, which is hard to test because aging is affected by hundreds, thousands of genes. But one of the hypotheses is that. We have, the context is we have a limited number of genes. Deena: It's not like you have one gene that's, that does x. At age YI mean, you've got this set of a limited set of genes and the genes are doing things throughout your life. Deena: And. Many of the genes I'll give a concrete example 'cause I think that [00:13:00] will help. Everyone's heard of the BRCA one and BRCA two mutations. Deena: So these are the mutations involved in breast cancer. So if you have these mutations, they elevate your risk of breast cancer. And. They were made famous by Angelina Jolie years ago when she found out she had these mutations. And so she preemptively had her breasts removed because she found out she had the mutations. So there have been studies showing that. Women in natural fertility populations. So in places where women don't use birth control these mutations exist in those populations. Deena: They're not common, they're not very frequent mutations, but they exist more than you would expect. You would expect a mutation, like the BRCA mutation to get weeded out. But they haven't. Deena: And so anyway, people have been puzzled like this. Why are there mutations around that increase your risk of breast cancer so dramatically.[00:14:00] Deena: And so people have studied it and they found out that in populations where no one is using birth control those women with the BRCA mutations have more children. So there's something about those genes having those mutations and those genes. Early in life, they actually help you have more kids. Deena: And so that's why mutations like that have stuck around is that they're good for fertility early in life. Deena: Nature cares less about what's happening later in life. Breast cancer in these women is usually happening later in life. And so, Deena: you know what's more important? Again, this is from the evolutionary perspective. This is not, I'm not saying that it's more important for us, personally as humans. Deena: But what succeeds over, evolutionary timescales are genes that help. An individual or help many individuals have more [00:15:00] children. There was another case study on the A POE four allele, which is well known for in increasing your risk of Alzheimer's and cardiovascular disease. Deena: Same thing with these. That, the a POE four allele, people who have it in natural fertility populations have more kids. Deena: So, so that is one of the main hypothesis on a hypothesis on aging is, Deena: all nature cares about are, those early. Reproductive events and Deena: It caress less about what's happening after you've reproduced or after you've produced most of your offspring. And there's of course costs associated with having lots of children and, so anyway, I think the post that you saw was a much larger scale study on hundreds of thousands of people in the uk. Deena: We [00:16:00] have lots of. Genetic information about these people, but also phenotypic information like how many kids they have when they had their first kid, et cetera. Deena: For some people when they died, we know when their parents died for, certainly. And so people have studied this question of aging on a genome wide scale and lots of people, so not just one gene in a population in, Bolivia, but. Deena: The entire genome and they found just what I said, which is it looks like the parts of the genome that allow some people to have more kids are also the same parts of the genome that cause them to die a little bit younger. So they have slightly shorter lifespans, but Mellisa: of Mellisa: con like condition related. Mellisa: It sounds like, like the things you've mentioned are Mellisa: Cardiovascular Mellisa: disease, Alzheimer's, Mellisa: breast cancer. I'm sure there are more, those are just Mellisa: examples. you're giving, But it sounds [00:17:00] like it's not just, Mellisa: it's Mellisa: not just a general lifespan Mellisa: differentiation. Mellisa: It's Mellisa: actually like the Mellisa: onset Mellisa: of degenerative conditions. Deena: Yes. Deena: But those are the things that make us die. Mellisa: Yeah. Mellisa: So, Mellisa: okay. So here's. Mellisa: a follow up Question, maybe you know the answer to, in Mellisa: those people that have these genes that would Mellisa: give Mellisa: them the ability to potentially Mellisa: have Mellisa: more offspring. Mellisa: is Mellisa: there any research suggesting that if they were to have less kids, Mellisa: that Mellisa: they would then reduce the likelihood of Mellisa: those Mellisa: degenerative? Mellisa: conditions? Deena: a great question. And the answer's no. So I'm talk, what I'm talking about here are genetic. Gene versions, what I'm specifically talking about. It's not like the experience of having the children, although that certainly could affect lifespan. And there are studies, that look into that. Deena: But these are genetic differences between people. So it wouldn't, it doesn't [00:18:00] matter that they have or haven't had more kids. Mellisa: Genes can still Express Mellisa: themselves. Deena: Exactly. And they will, right? That, let's say that woman was using birth control or that woman and didn't wanna have children, or, she still has the genes that would have allowed her to have more kids had she not been using birth control. Deena: And those still, those genes are still gonna express themselves late in life. As slightly Mellisa: This may, this helps make sense of why these studies. Mellisa: are done in natural fertility environments where Mellisa: You're Mellisa: not having Mellisa: to Mellisa: factor for Mellisa: birth Mellisa: control and Mellisa: that kind of stuff. Mellisa: Okay. Deena: Yes. Although that big study that I mentioned was not done in natural fertility populations and the signals, we still saw the signals, which was somewhat impressive. Mellisa: Okay. Mellisa: This is Mellisa: Really, Mellisa: interesting and still upsetting to me. Deena: me. Yeah. Mellisa: just Mellisa: Because Mellisa: I, Mellisa: totally Mellisa: can put Mellisa: on the Deena: the hat, Mellisa: to an extent that you're [00:19:00] describing, which is this Mellisa: e evolutionary Mellisa: perspective. But of course, I Mellisa: also Mellisa: feel Mellisa: a, Mellisa: I Mellisa: feel compelled by Mellisa: another Mellisa: narrative, which is Mellisa: perhaps a more spiritual or philosophical narrative about, Mellisa: human Mellisa: existence and human meaning. And Mellisa: all of these things. Mellisa: So it's just Mellisa: interesting to, to try to balance Mellisa: all Mellisa: of these different Mellisa: aspects. let's talk about, Mellisa: oh, go Mellisa: ahead. Deena: ahead. Sorry. Let me just interject there and say that lifestyle factors, diet, those are really important. And I would say that, one of the biggest problems we face as humans today is that our lifestyles and diets are so very different from the lifestyles and diets of our ancestors. Deena: Because really that's when our genomes evolved, our genomes are. Constantly evolving. It's not like we have stopped evolving, but this current way that we live is just a [00:20:00] blip of human evolutionary history. Deena: And so for the thousands, tens of thousands, hundreds of thousands, even millions of years that humans have been evolving this is not how we lived. Deena: And so I do think that a lot of the health challenges that we face now, is it's because of this mismatch between how we're living and how and what our genomes are expecting. We're not expected to be consuming huge amounts of very concentrated sugar, for example. There were, there was sugar around but not, Deena: the way that it's, consumed now. Mellisa: Yeah, Mellisa: Yeah, Deena: So, I don't know if that addresses, your disappointments but I want to make sure that people understand that there are absolutely so many things that you can do for your longevity and your health span. Deena: And, I think that's really what most people should be focused on. [00:21:00] So, there's a whole movement of people who think that we can extend human lifespan. Deena: It's about 120 years now. So, there's like the celebrity people who wanna live until they're 150 or 200. That's, at this point, I think a little bit silly. Instead we should focus on living those 120 years as healthy as possible, and that is doable. I. Deena: And we know, I'm not gonna say it here because, I don't wanna nag anyone, we all know the things that we need to be doing. Deena: Exercise, healthier diets, the obvious things, sleep Mellisa: yeah, Deena: friendship, Mellisa: Friendship Mellisa: community Mellisa: Is so. integral, And that's Mellisa: something that has come up again and Mellisa: again. that quality of life and quality of health is so, so interconnected. Mellisa: to a Mellisa: lot more than just dietary Mellisa: factors. The actual Mellisa: Way Mellisa: that we live our lives, Mellisa: the kind of community, Mellisa: that we're in, the way that we're making meaning of our Mellisa: ourselves, of our experiences, of our relationships is really [00:22:00] huge. Mellisa: Yeah. Mellisa: Yeah. Mellisa: Which I think does tie into the menopause question because. Mellisa: This is one of Mellisa: the Mellisa: points that actually Mellisa: brought Mellisa: me to finding you and to being really interested in your work Mellisa: is this Mellisa: question of what is the Mellisa: evolutionary Mellisa: or functional purpose of menopause? Mellisa: Like, why do we stop producing hormones as women? Mellisa: I know that it does change for men as well, but not nearly in the same way that it does for women. Mellisa: And the Mellisa: more Mellisa: I have learned about Mellisa: the. Mellisa: quote unquote Mellisa: Harmful effects of the loss of estrogen in the body, in terms of the onset, Mellisa: of disease, osteoporosis heart Mellisa: disease. Mellisa: Like, there's just so many things Mellisa: that Mellisa: can begin to occur and so often do for Mellisa: women that it Mellisa: just really makes you go, okay, why do we experience, men experience, menopause? And I, am, Mellisa: by Mellisa: definition Mellisa: myself, I am the kind of person Who Mellisa: who Mellisa: takes a pretty naturalist approach. Like, I don't want to Mellisa: [00:23:00] intervene with Mellisa: very much. I grew up on a farm in northern Canada Mellisa: there's just a lot that Mellisa: I see as Mellisa: like, it's the way it is for a reason. Mellisa: So that's how it should be. Mellisa: And I'm Mellisa: really Mellisa: looking more closely at that with this menopause thing. So, I'd love to hear from your perspective, I know about the grandmother hypothesis, Mellisa: which we can, we can talk about that, but I'd love to know. Mellisa: From Mellisa: your Mellisa: perspective, Mellisa: what really is going on in the female body, why do we go through menopause? Mellisa: Is Mellisa: it Mellisa: functionally Mellisa: necessary? Deena: Okay, so that's a big question. So let me try and tackle it sort of piece by piece. So, first of all, menopause is very rare. So, I'm an evolutionary biologist, so I'm always thinking about any trait in humans, but in the broader context. Deena: So menopause is very rare. It does exist in a few other species. There's strangely all toothed whales, [00:24:00] so orcas. Beluga Whales, narwals and another species, they're called short fin pilot whales, Mellisa: My daughter would know all of these. Mellisa: by the way. Deena: She said she loves marine mammals. Mellisa: Yes. Deena: So we know the most about orcas. So Orcas actually have a similar lifespan as humans. Deena: So many of them will live into their nineties. They also have a very similar reproductive span, the females as human females, so they will stop reproducing in their forties. So that's really interesting because, one of the. Thoughts on menopause is that it's just specific to humans that it's, humans have longer lifespans now and it's not really a natural life history trait is what it's called because, it was really just uncovered when humans started living longer and that, that is very misleading. Deena: [00:25:00] And I won't get into the math of it, but. We have lots of EV evidence that humans have been living past the age of menopause for some time. It's not like, Deena: Something that emerged in the last couple hundred years. So I. The fact that these other animals go through a very similar transition halfway through halfway into their lives suggests that it's like a real trait. Deena: It's not this thing that was artificially uncovered when we started taking vaccines and antibiotics. Deena: So menopause is rare. And it is puzzling on evolutionary grounds because, like we talked about earlier, it's all about reproduction. And so it really doesn't make sense that Deena: all the females in a species would stop reproducing halfway through their life. Deena: That is the puzzle. I. Before we get into the theories on it, and I will say we don't have an answer, so I'm gonna disappoint you and your listeners here. We don't have a solid [00:26:00] answer. And anyone who tells you that they know the answer, is misleading you, we really don't know. These types of traits are really hard to study 'cause they don't leave a trace in the fossil record as an example. Deena: We don't. Know how long people were living, and we certainly don't know when they were going through menopause. So there are hard traits to study. Deena: One thing that I think is interesting for people to know about menopause is Deena: this difference between men and women like you mentioned. Women are set up to have menopause because of the way we produce our gametes or our eggs. Deena: Men are not set up in the same way to lose the ability to reproduce 'cause they have these stem cells that allow them to continue producing sperm. We don't have those. So I don't know if you've covered this in earlier shows, but we make all our eggs as fetuses. And once we're born, like we cannot make any more eggs. Deena: So we [00:27:00] basically stock up our ovaries with eggs, and then we've, we're stuck with that pile of eggs, for the rest of our life. And this is not unique to humans. This is true of all mammals and actually birds. So we make this pile of eggs, and then we've got a, make do with what's there. Deena: And that's interesting in and of itself. Why would females have this completely different strategy of making their eggs? Arguably Deena: making eggs and making offspring like this is the most important thing, right? From the evolutionary perspective. So why would we do that? Why would all mammals and birds do that? Deena: And one of the ideas, and it does have quite a bit of support, is it's this idea that it's safer for female mammals to make their eggs this way. So [00:28:00] as everyone knows, female humans all female mammals, the. Producing offspring involves a lot of investment, just making the egg. When you compare a human egg to a human sperm cell, we invested a lot more into making one egg than a man invested in making one sperm. The sperm is much smaller. It's not packed with all of the goodies that a human egg is packed with, beyond that, we are pregnant for nine months if we're a human. We're nursing our babies for quite a long time, so this is a really big investment. Deena: And so female animals in general because. They're making such big investments in their babies, have all these systems of quality control. So we have, as an example and something that I've studied and I'm really interested in, at very early stages of human pregnancy our uterus actually [00:29:00] weeds out embryos that its senses are unhealthy, that its senses are not developing normally. Deena: Like our uterus actually prevents those embryos from implanting. Why would it do that? Why would it evolve that mechanism? Because. If it lets that embryo implant, that embryo is probably not gonna make it, but it may take up three or four months of time and investment until that embryo is dies. Deena: And so, for a female animal, that's a big deal. That's three or four months that it's not investing in a different embryo that would make it. So my point is we have lots of these strategies again, not just humans, but all mammals. Two. Increase the chances that we're investing in offspring that are actually gonna make it and reproduce themselves. Deena: And so the thought is that, we make all our eggs up front [00:30:00] because that limits the, one thing I didn't mention about making sperm throughout your life. Those stem cells are continuing to divide over and over again over the course of a man's life. And that's great for making lots of sperm, but what happens is that those cells start accumulating mutations and mutations tend to be harmful. Deena: It doesn't matter as much for a typical male mammal because. It's not really investing anything in reproduction other than this isn't true of course for all species, but for many species, all the male is contributing is his sperm. He's not Deena: carrying the children. Nursing the children, caring for the children, Deena: the female Mellisa: diapers. Deena: Changing their diapers. Exactly. Female mammals are school. Yes. So, so, sorry, backtracking a little bit, 'cause I'm going down this rabbit hole. This is a really interesting [00:31:00] question to me, just this difference in. This basic difference in how we make our eggs and sperm and the reason we make our eggs the way we do, makes a lot of sense when you think about it in terms of this, broader context of, how much females invest in their babies and having ways to, keep our eggs, our babies, our embryos, our babies healthy for for as long as possible. And diverting our energy into those offspring that are gonna make it. Deena: so Mellisa: so let me make sure I'm understanding this. So essentially you're Mellisa: saying that the conditions in utero, Mellisa: when a fetus Mellisa: makes Mellisa: all of those eggs up front. Mellisa: are Mellisa: likely to have to be better closed conditions for the quality Mellisa: of Mellisa: that overall batch of eggs that female is going to have Mellisa: versus Mellisa: the Mellisa: sperm that's created over a [00:32:00] lifetime that is, can be affected by mutations and whatever else may occur Mellisa: in that Mellisa: male lifespan. Is that a Mellisa: good Deena: Absolutely. It's all about cell divisions. Deena: The more cell divisions, something goes through the higher, the chance that a mutation like cancer as an example, but lots of other things the higher the chance that those things are gonna come about. So females, the limit, the number of cell divisions that their eggs go through, they basically make 'em, and then they. Deena: Don't touch 'em until they need to be used. It's not a perfect system. Other things can happen to eggs. And they do, in older women, the proteins that hold chromosomes together, they, the, they start to fall apart. And so that's why in older women there's higher chances of down syndrome and, other chromosomal problems. Deena: But that's something separate from the mutate, this gene mutations that I'm talking about. Those happen during cell [00:33:00] divisions. Okay. Mellisa: So back to Mellisa: the theories about Mellisa: the Mellisa: limits on Mellisa: The reproductive Mellisa: span of females. Deena: cells. Mellisa: You Mellisa: said that there really is no Mellisa: answer that is Mellisa: clear. Mellisa: What Mellisa: are Mellisa: some of the. Mellisa: possibilities that Mellisa: relate to what you've just shared, Deena: Right? Deena: So. Deena: You mentioned the grandmother hypothesis. So this is one of the well-known, best known theories on why we go through menopause. It's actually not a hypothesis on why we go through menopause. It's really a hypothesis about why humans evolved to live longer. And so what do I mean by that? When you look at chimpanzees, so these are our closest living relatives. Deena: Often when we're studying traits in humans and we wanna understand when and why they evolved, we look to chimps. Chimps go through menopause at about [00:34:00] 50. I just explained that all female mammals and birds are set up for menopause. Deena: What's unique in humans and killer whales is that we live so much longer, past, the age at which we run out of eggs. So menopause itself is not that surprising in any species. What's surprising is and many animals will, especially animals living in captivity, they will live longer. Deena: They'll stop reproducing and then they'll continue living a few years. Deena: Unusual in the species that go through menopause, humans, killer whales, those other whale species, is that we live decades. It's not just, we live a little bit beyond the age we run out of eggs. Running out of eggs is exactly what you'd expect. Deena: What's unusual is that, we live so long beyond, so the grandmother hypothesis. Isn't an explanation for menopause. Menopause is, we sort of inherited it according to this hypothesis. We inherited it from our ape [00:35:00] relatives. The simplest explanation is chimps go through menopause at 50, so our ancestors must have gone through menopause at 50. Deena: What's different in humans is that we started living longer, and so the grandmother hypothesis is an explanation for that. Why did humans evolve to live longer? And longevity is definitely a trait. That evolves. It is a little bit confusing because of very recent technological medical advances in humans that make us live even longer, but Mellisa: so suddenly, like such a dramatic Mellisa: increase. Yeah. Deena: Exactly. But humans. Live a long time relative to chimps, our maximum lifespan is much longer than chimps. Whether you've taken the vaccine or whether you've taken the antibiotics or not. So in places where people don't take those medications, they still live quite a long time. Deena: And so that's the grandmother hypothesis. Deena: It's this idea, it's this hypothesis [00:36:00] about why humans started living longer and. The idea is, Deena: We were humans, were living in these groups. We were living in close family groups, and there were some. E there must have been some ecological changes that sort of spurred us, some things to change in our populations. Deena: And so Kristen Hawks, who's sort of developed the hypothesis after her work with the hazah in Tanzania, this is a hunter gatherer tribe. She studied the hadza and noticed that the grandmothers in these small family groups. Played a really important role in their families, and specifically what they were doing was helping feed their young grandchildren, their weaning grandchildren, and the grandchildren. Deena: Kids who were to or [00:37:00] three would never be able to process, dig up the like potatoes or tubers. Process them, mush 'em up, they never would've been able to access those calories without the help of those grandmothers. And so those grandmothers. Who were heavily involved in feeding their grandchildren. Deena: They had more grandchildren survive, so they were basically passing on their genes through their grandchildren. And so the grandmother hypothesis is really a hypothesis about human longevity. So why did humans start living longer? It's because these grandmothers develop these new behaviors of. Feeding their grandchildren. Deena: And so they were passing on more of the genes than, more of the genes involved in these traits of, the behavioral traits and the longevity. They were also living, they must have been living longer to provide these services for their grandchildren [00:38:00] and. That set up this feedback of, more grandchildren slightly longer lives. Deena: Other changes, shorter intervals be between births. So if a grandmother was helping feed her grandchild, Deena: then her daughter could wean, start weaning her children earlier, and so she could actually have more kids by reducing the distance between births. Mellisa: right. Deena: So it was a really appealing hypothesis and I think that it probably was, it probably played a role in some of these traits that we're talking about but I don't think it answers all the questions. So, the truth is you still have, you still pass on more of your genes through your children. And so the question is, why didn't why didn't human women evolve a later age at menopause? Deena: That's really the question. We know that elephants. Female elephants. [00:39:00] The grandmothers are very important sources of knowledge for their entire groups. These are matriarchal groups but the females continue having their own kids. Deena: So, why didn't that happen in humans? Deena: I'm really interested in a species of whale. They're called bowhead whales. These are the longest lived mammals in existence. They live over 200 years. They're incredible. They live in the Arctic and sub-Arctic. As far as we know. They don't stop ovulating. Deena: They continue having babies. And so, I described this setup of why we go through menopause. Deena: We make our eggs up front and if we live long enough, we run out of eggs. That's essentially what happens at menopause is Deena: we don't completely run out of eggs, but the numbers of the number of eggs goes below a threshold where, we can't support cycling anymore because there aren't enough [00:40:00] follicles making the hormones that talk to the brain, that tell the brain to, keep our cycles going. And so we basically run out of eggs, but bowhead whales don't. Elephants don't, and so there's very easy ways to evolve a longer reproductive span, and many species have done it. And so the question is, why haven't humans, and so other folks have come up with other ideas on why. Deena: Reproductive span in humans has kept, was kept short. As an example, this is a more obvious one. It alone doesn't answer the question, but, childbirth in humans is very difficult and it becomes riskier as you get older. Deena: More older women die in child childbirth than younger women. Deena: But that increase in child and maternal death is not so high that it would explain why we have to go through menopause at [00:41:00] 50. It does increase a bit, but it doesn't increase dramatically. It's not like it goes up to 50%. For women having babies, not in hospitals, it's like 3 percent or something just, terrible if you're that one woman, but it's, it's, it's not enough to explain why humans must go through menopause at 15. Deena: Yeah, and so there are other ideas one that's fairly complicated. It's called the reproductive conflict hypothesis, but the idea is, there's limited resources. In, in these early human groups and older mothers and younger mothers are reproducing at the same time. And, there's conflict over those resources and the conflict is greater for older, the older women are related to the younger. Deena: Women's children, they're her grandchildren, but the younger woman might not be related to the, because of the way that humans have to [00:42:00] move around not just humans, all mammals, you know, mammals typically want to avoid inbreeding and all mammals do this naturally. And so typically either males or females at maturity leave the group. Deena: So, anyway, the, the details are a little bit complicated, but the idea is, in these early human groups, there was potentially conflict between older and younger females. Over those resources for reproduction, and it made more sense for the older females to stop reproducing and instead divert those resources to the grandchildren. Deena: So it's actually a combination of these hypotheses. Yeah, Mellisa: which, which seems like, I think I heard someone say once that. If you are, if you are looking at option A and option B, the answer is almost always going to be some combination of A and B, like there's, it's so, so rare in life that there would be a very clear, super linear, super [00:43:00] definable reason for something this complex and it does just seem everything that you're saying, I'm just thinking about all of the incredibly complex social dynamics that are there. Mellisa: specific to human populations. Not that other mammals don't have really developed social ecosystems. They do, but not, not to the level that humans do, and what you just said too about the, the resource conflict also makes sense of the opposite direction of, male. Male mammals, or I will even just say humans enjoying the company of younger women, right? Mellisa: Like it, it makes, it makes sense of it on that level too. And I think, I think for me, as I ponder all of this, which I often do, but now I'm doing so with a lot more information, thanks to you. I think about those. Intergenerational factors, which if you look at [00:44:00] any traditional society, I don't think you have to follow a hunter gatherer society in the middle of nowhere to see that most societies really have that intergenerational component where. Mellisa: People are living intergenerationally grandmothers are really invested in their grandchildren and that's we can still see that today. And I think that that it frees up resources in all directions, right? Like mothers can be. Doing what they're doing, grandmothers can be doing what they're doing, fathers can be doing what they're doing, and that probably worked really well for a long time. Mellisa: Now it seems to be breaking down in our society because we have, obviously we have different goals a lot of times for our modern selves, but traditionally speaking, that worked well for a long time, it seems. Deena: Yes. And I think. I think a lot about grandmothers just in the context of my own life, because I live very close [00:45:00] to my mother and my mother in law, and I think a lot about their relationship to my kids and to myself, and, my observation is that they get a lot of pleasure, not necessarily in, Babysitting my kids all day, every day, like they don't, they're not interested in that, but they get a lot of pleasure in being involved in their grandkids life. Deena: And I think, however it is that they, my mom, her love language is buying gifts for people, so she takes my daughter out. Anytime she takes my daughter out, she's buying her shoes and, clothes and and I think what's really interesting, people don't often think about pleasure as something that evolves, but actually, our, evolution's very sneaky. Deena: It, it, it, there are certain things that we have to do, like eat, as an example. If we don't eat, [00:46:00] we don't survive. If, we don't have intercourse, we don't have children. And so, evolution has actually created these pleasure and reward systems in our brain to trick us into doing these things that are critical for our reproductive success. Deena: We know that that's why eating, delicious foods, why we love that, why that's a pleasurable experience. Why sex feels good, these things. Evolve for a reason, these sort of pleasure, these experiences that our brain tells us is pleasurable. Yeah. And I see that with my mother and my mother in law. Deena: I think, this pleasure that they have being involved in the lives of their grandchildren, I think that's something that evolved. And if you look at a different species where there's no grand parental involvement, it's, the. These it's a solitary species as an example, you take care of your [00:47:00] kids until you can read them and then that's it. Deena: Nothing like this exists, right. And those species I think if you look at those whales that go through menopause, what's really interesting is that they are very close knit social species where, there is this intergenerational groups are intergenerational. Deena: There's knowledge and information that's passed down even in these whales. So that's not specific to humans. And I, and I think that these traits definitely played a part in this. Trait of menopause and longevity evolving certainly. Mellisa: So really quickly, you, you mentioned the evolution of pleasure, and I think that this is one of the other mysteries of the female body because orgasm is not. Mellisa: a reproductive necessity for a female. So do you think that it's related to what you just said, the, the sort of [00:48:00] sneaky the sneakiness of evolution to, to create that, that desire or that openness to sexual experience for the purpose of reproduction? Deena: Yeah. That is a big question. And I could talk about this forever. Mellisa: Maybe yeah, maybe we can have, we can do another episode about, about that. Deena: Yeah, the female orgasm is, when I was researching my book, this is one of the most fascinating topics. Partly because it's such a contentious topic in the field of evolutionary biology. There have been a number of people who've studied this and orgasm in males, there's no question why they have them and why they feel good to males. Deena: It's, as I said, traits that are required or critical for our reproductive success, they tend to evolve to be pleasurable. Our brains tell [00:49:00] us that those things feel good. For males, though they can't reproduce without an orgasm, right? They, the Release of sperm is tied to it's tied to that orgasm, right? Deena: It's, it's all connected. And so, the debate about the female orgasm has to do with. Why it exists in females where they're not required, right? There are, we know that a female woman does not need to have an orgasm to reproduce and many don't a vaginal orgasm. And so, yeah, this is a big question and I think we're going to need to do another podcast Mellisa: episode. Mellisa: Deal. Deal. I'm pretty sure that this will be, this will be the perfect teaser and we will get a lot of requests for that second episode. That's absolutely perfect. Okay. So I do just, maybe the, maybe we can wrap up with this [00:50:00] instead. That is, I. I'm really curious, you're talking about these evolutionary timescales and, the things that Maybe have been uncovered in the last couple of 100 years where so much research has been going on may may artificially cast light on certain things. Mellisa: But I'm curious from your perspective, evolutionarily, and maybe you can also just briefly. Describe the relationship or the difference between evolution and epigenetics, but what do you think is happening right now in terms of what is changing for our species? Because 1 example that I have, I'm a birth worker and, have been involved in the birth space for almost a decade and there is research showing that because of the increased rate of cesarean, that the actual anatomy of the pelvis is starting to change for women. And I'm curious your thoughts on that and how, how quickly can things change? What is changing right now for [00:51:00] humans? Deena: So that's a great question. Um, we have to define what change means. I think, there are things that. Change, if, if you don't give birth through your birth canal for that one woman that might affect the ultimate shape that her canal takes on, as she ages. But that's not a change that's going to be inherited. Deena: In the next generation, if that makes sense. Deena: People often think that humans are not evolving and that is absolutely not true. Deena: There's no reason to think that, because, we're so technologically advanced that we have stopped evolving because modern, of modern medicine, we have stopped evolving. That's, that's not true. And actually there have been some studies showing that our reproductive spans have been getting slightly longer. Deena: So both [00:52:00] the age that girls are having their first periods and Is earlier. Yeah. It is earlier. I think much of that is dramatic changes in lifestyle, like we talked about earlier, we know that for example, better fed girls are going to, get their period slightly earlier than, an anorexic girl or so some of this is just built in to the system that has evolved quite a long time ago, you know, it's not like our, it's not like our genes tell our bodies to hit puberty at this exact time and to go through menopause at this exact time. There's a lot of flexibility built into the system and depending on how much you're eating and how stressed out you are, you may hit puberty, you may go through menopause earlier or later, but there's evidence that there have been genetic changes to the timing of puberty and the timing of menopause. Deena: Very, very slight changes. So, over a couple of generations, we're talking about, days and weeks not [00:53:00] years. And so, practically speaking, this isn't going to, Affects a woman's quality of life, she's, she's not going to be able to have kids five years later because of these, population level differences that are happening but they are, we think that they're happening. Deena: Um, again, most evolutionary change is very slow. And so, again, practically for women, it's not going to make a big difference in our lifetime, in our daughter's lifetime, these, these. genetically encoded changes. The thing that you mention about the birth canal is very interesting. Deena: I haven't read about this, but I, I will. I'm curious. Mellisa: I'm curious about that in the follow up. We can talk about that in the follow up episode. Deena: I'm curious. I didn't realize C section rates were So high Mellisa: that it's not necessarily that they're so high. In some parts of the world they are, but overall the global C [00:54:00] section rate has gone up just because of access to, there's, there's a number of factors we can, we can definitely, we can broach that another time, but some of it is just pure access, right? Mellisa: People, some people that would have just died in childbirth before now have access to cesarean, but there are a lot of unnecessary cesareans as well, right? Deena: Right. And so, those are very, Deena: If C sections are allowing women who would have otherwise died because their birth canals were too small, if, they're allowing many women to, Have babies in theory that could slowly change the size of the birth canal, but I, can't imagine that we would be able to observe that on such short time scales, but I need to see, we think about evolution needing to be slow, but it doesn't always proceed slowly. Deena: So, got to look at it case by case really. Mellisa: For sure. This is so, so, so helpful. I know we have to wrap up [00:55:00] because you've got to go, and I think we're definitely going to have to have another conversation. Can you tell everyone a little bit more about your book and where to find it? Deena: Yes, so, I wrote a book, A Brief History of the Female Body, it's available anywhere that you buy books, Amazon, Barnes and Noble bookstores it's really a story about why our bodies the way, are the way they are, but from the evolutionary perspective. Deena: So why do we have breasts? Why do we have orgasms? Why do we have periods? Why do we go through menopause? And I don't pretend in the book to have all the answers, but I take my readers through, all the ideas in many cases, the one that I think is the most reasonable or the set of hypotheses that I think are the most reasonable. Deena: And I think it's really important for women to understand the history of their bodies because it. It [00:56:00] has such a, I think when we're thinking about our own health I think it's really important to understand why we have some of the health challenges that we're having now. And a lot of it has to do with the way that our bodies evolved and the way that we're currently living our lifestyles. Deena: Yeah. So often we're pushed to take a drug and many people prefer, like the easy solution, but I, like you tend to be suspicious of intervention unless it's really critical. And there's so many things that we can do about our diets and lifestyles that that women should know about and understand why. Deena: It's 1 thing to tell someone to eat healthy or to eat more green vegetables or whatever, but understanding why those why we should live a certain way and why we should eat a certain way, I think helps. It certainly helps me make better choices. Knowing that the deeper context. Mellisa: [00:57:00] Yeah. And just very, very quickly, I know you're not a medical expert, but from this perspective of the midlife loss of hormones and all of the deleterious effects that that can cause like osteoporosis, et cetera, et cetera. What do you think about hormone replacement therapy? Like, does that feel like a advantageous intervention? Deena: I'm of two minds. A lot of women don't think twice about taking birth control. And I certainly didn't when I was younger and the hormone replacement therapy formulations, and even the amount, the hormones are much lower than, the amounts in a birth control pill. Deena: There's this long history of the studies that. Studies on hormone replacement therapy. I'm sure you've gone through this with other podcast guests. Um, there's, there's a lot of fear around HRT that there isn't necessarily about birth control, which Mellisa: is, it should actually [00:58:00] be the other way around it based on my. Mellisa: Yeah. Deena: I, I'm on the fence. I think it's the right answer for lots of women. I don't think it's the right answer for every woman. Yeah. And I also tend to be a little bit suspicious of, things being pushed on me that don't feel right. Right. Yeah. So I'm actually headed right now to an appointment with my primary care doctor. Deena: And I'm going to broach this conversation with her. These are the symptoms I'm having. What do you think? And think I'm willing to experiment and see how that goes. Um, the thing that you always worry about with interventions is side effects. And I have a good friend who after reading my book decided to try some estrogen therapy and she said it works miracles. Deena: She had this rage that all of a sudden went away. But yes, [00:59:00] but she developed really dry eyes and she's an eye surgeon. And she said she couldn't function with such dry eyes. So, there are always pluses and minuses and I think every person has to weigh individual. Mellisa: Yeah, it's so individual. Mellisa: And I think that too comes down to. As with anything, working with a provider that can be really responsive, there's no one size fits all approach to this kind of stuff. Like, yeah, maybe this doesn't quite work, but can we try this instead? Yeah, for anybody listening, I highly recommend listening to our episode with wise and well, I'll share a link in the show notes to that too. Mellisa: And thank you so much, Dina. You have just been a wealth of. Wealth of wisdom and information. I can't wait to share your episode. I will definitely share the link to your book and highly recommend everybody get a copy of that. Thank you again so much for joining me today and I'll look forward to doing another [01:00:00] episode with you soon. Deena: Yeah, I had fun. That was, that was great. Thanks for the conversation and for absolutely asking me so many fun questions that Mellisa: you bet there. I have many more. [01:01:00]