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Insights Into Menopause Come from Killer Whales

A fun fact about human people with uteruses is that we are one of the very few species in which menopause happens and the person can continue living a long and happy life for many years afterwards. There are only three species in the world in which females live for significant years after they lose their fertility: humans, pilot whales, and killer whales. So that’s a little weird. Most mammals have pretty similar reproductive patterns, and it does make an evolutionary sense that after an animal has stopped being able to produce babies they don’t stick around for too long and take up resources. So why on earth do we have menopause?

There are a few theories that have been floating around for a while. One suggests that technology and medicine simply changed our lifespans so that women lost their fertility at about the same age but kept living. But the most common hypothesis was called the Grandmother Hypothesis, which suggests that women stop bearing children and move to caretaking roles that improve the chances their children and grandchildren have of surviving. Of course there’s nothing about this hypothesis that explains why humans but almost no other species do this, or why it would improve one’s evolutionary chances more than having your own kids (who are more genetically similar to you than your grandchildren).

But studies on killer whales might give insight into the mechanisms of menopause. One of the most striking things that orcas, pilot whales, and humans all have in common is the patterns of habitation that offspring use. In all of them, children either continue to live with their parents into adulthood, or only daughters leave and move to their mate’s family. That means in all these cases, only some of the mother’s grandchildren will be in close proximity to her.

For killer whales, this translates into a whale’s grandchildren through her son spreading into different pods, while her grandchildren through her daughter stay in her pod. Statistically, that means it’s most beneficial to put resources into the son, as his children won’t be competing with each other, since they’ll be spread among different pods. And that’s exactly what studies of whales found: female, menopausal whales put the most effort into keeping their sons alive and healthy. An adult male whale was 14 times more likely to die in the next year if his mother died. It turns out that these grandmotherly whales do actually help their offspring to survive, particularly by providing information about where choice sources of food are. During lean years, researchers found that the menopausal whales took on an even greater importance in the pod.

So why does any of this matter beyond the interest of cool scientific findings? Well it certainly calls into question many of the assumptions that people make about how evolution has changed us. Especially in fields like evolutionary psychology, many people operate on the assumption that all of the adaptations that have got us where we are happened in order to allow men to have more sex and to allow women to keep their mates close to help raise children. What these insights ask is whether more offspring is really always better, or whether there are intellectual resources that parents can pass to their offspring. These findings call into question some of the most basic ways that science falls into sexism, and provides some evidence that smart women are completely necessary for the survival of the species. It might even push some evo psych proponents to try using actual science instead of assumptions and stereotypes.

Thanks menopause!

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Olivia

Olivia is a giant pile of nerd who tends to freak out about linguistic prescriptivism, gender roles, and discrimination against the mentally ill. By day she writes things for the Autism Society of Minnesota, and by night she writes things everywhere else. Check out her ongoing screeds against jerkbrains at www.taikonenfea.wordpress.com

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  1. I have a complex relationship with the label “evolutionary psychology.” On the one hand, an awful lot of nonsense and bad science has been and continues to be promulgated under that banner, and the popularization of half-formed, ill-supported, and simplistic hypotheses by some scientists and writers like Robert Wright has given rhetorical ammunition to those like MRAs, who find it convenient to co-opt the label “science” to rationalize their regressive social beliefs.

    On the other hand, there is more to evolutionary psychology than just that. The core idea, that certain aspects of human cognition and behavior can be understood as products of a process of evolution which has shaped them in specific ways, is fairly uncontroversial within biology; what is unknown is which aspects can be explained in this way, in what manner they have been shaped, and to what extent the evolutionary explanation has explanatory priority. This is an approach to the study of behavior which has been extremely successful in other animals, and while culture is a tremendously powerful influence in humans which must not be ignored, there are many ways in which human behavior also resembles that of other animals, and is amenable to investigation with similar methods.

    Olivia, you wrote, “Especially in fields like evolutionary psychology, many people operate on the assumption that all of the adaptations that have got us where we are happened in order to allow men to have more sex and to allow women to keep their mates close to help raise children.” This is a little vague — who are the “many people”? The lay public? Science writers? Scientists? And which scientists? A researcher’s approach to evolutionary psychology might vary dramatically depending on whether her original training is in psychology or evolutionary biology. I would expect that very few researchers with a strong background in the study of animal behavior would make that assumption, as it would imply that human behavior is vastly simpler than that of most other animals, who evolve novel behavioral traits for much more complex reasons than those. On the other hand, it is certainly true that some professional scientists (e.g., Satoshi Kanazawa) espouse such simple-minded approaches to evolutionary psychology, so your arrow is not off the mark.

    My friend, colleague, and collaborator, Dr. Lauren Brent, studies killer whales, participating in the research program on the evolution of menopause described here. (A recent paper of hers was published as an open access article in Current Biology, so you can read the primary work for free.) Once during a discussion on the merits or lack thereof of evolutionary psychology, she told me she considers her broader research program to include evo psych. I can assure you that Lauren’s thinking about evolution is by no means simplistic, and is well-informed by a solid grounding in animal behavior (her original training was in primatology). Our discussion about evo psych was a few years ago so her thinking may have changed since then, but I think it’s worth noting that at least one researcher on the project you’ve described sees her work as generally compatible with evo psych.

    1. Hi biogeo. Hope things are going well for you. =)

      The core idea, that certain aspects of human cognition and behavior can be understood as products of a process of evolution which has shaped them in specific ways, is fairly uncontroversial within biology;

      Actually, I think even outside of biology, this idea, as you’ve expressed it here, is fairly uncontroversial (though I might nitpick that cognition and behaviors are better described as shaped or influenced by evolutionary forces rather than as products of such forces, but I digress).

      The problem, of course, is what you bring up next.

      what is unknown is which aspects can be explained in this way, in what manner they have been shaped, and to what extent the evolutionary explanation has explanatory priority.

      And herein lies the problem with evo psych approaches to human behavior. It is just not possible to tease these things out. For every explanation invented under the evo psych rubric, we could come up with others that do not appeal to evolutionary adaptation. We do not have evidence of specific behaviors in pre-history outside of some inferences from the archaeological record, which is inherently incomplete. Thus, there is no way to draw detailed and nuanced comparisons between behaviors that people engaged in pre-historically with behaviors that people engage in today. All we have are inferences and conjecture, which are easily colored by all kinds of biases.

      This is an approach to the study of behavior which has been extremely successful in other animals, and while culture is a tremendously powerful influence in humans which must not be ignored, there are many ways in which human behavior also resembles that of other animals, and is amenable to investigation with similar methods.

      The issue I have with this is basically what does it mean for a human behavior to “resemble” that of other animals? In order to draw such comparisons, don’t you have to strip culture out of the equation, since humans are the only animals with culture, particularly if we consider how thoroughly cultural human cognition is?

      To me, the idea that “it looks similar to me so it must have been shaped by the same forces” is highly problematic.

      1. I agree.

        We’re sentient creatures capable of abstracting ourselves, making long-term plans, and learning complex ideas from others. Any sort of simple deterministic model of human behavior falls apart 3 inches out of the gate.

      2. Hi Will, thanks as always for the thoughtful response!

        Actually, I think even outside of biology, this idea, as you’ve expressed it here, is fairly uncontroversial (though I might nitpick that cognition and behaviors are better described as shaped or influenced by evolutionary forces rather than as products of such forces, but I digress).

        It’s a fair enough nitpick. In general when I say “trait X is a product of evolutionary forces” I don’t necessarily mean that evolutionary factors are the sole explanation for trait X, so “shaped” is probably somewhat more precise than “product.” In general I’m a strong adherent of Niko Tinbergen’s “four questions” approach to understanding animal behavior: a complete explanation involves historical contingency in evolution (phylogeny), adaptive significance or function, individual developmental history of the animal (ontogeny), and physiology (mechanism). Any one of these four explanations might be considered a “cause”, but they address different levels of causation.

        We do not have evidence of specific behaviors in pre-history outside of some inferences from the archaeological record, which is inherently incomplete. Thus, there is no way to draw detailed and nuanced comparisons between behaviors that people engaged in pre-historically with behaviors that people engage in today. All we have are inferences and conjecture, which are easily colored by all kinds of biases.

        Well, I think that depends on what kinds of behaviors you’re interested in trying to explain. I suspect you are thinking about fairly complex human behaviors of the sort that are either entirely dissimilar from animal behavior (e.g., language and culture) or so dramatically more complex in humans that the relationship with animal analogues is unclear (e.g., mate bonding). In this case our “sample size” for evolutionary comparisons is effectively one, so reasoning about evolutionary influences on these behaviors is thorny to say the least. But some interesting human behaviors are in fact shared by other animals. For example, gaze following, the ability to look at a social partner’s eyes, infer where she is looking, and orient your own gaze to the same focus of attention as your social partner, is something that almost all humans do effortlessly, and often unconsciously, but which is fairly rare among animals. Most or all nonhuman primates seem to do it, there’s some evidence that crows can do it, and I believe I’ve read reports that dogs can do it, but most animals can’t. The neurobiological mechanisms supporting gaze following even seem to be conserved between humans and monkeys. So we could try to look at the evolution of this trait by looking at various species that do or don’t have it and trying to understand what about their behavioral ecology seems to explain the presence or absence of gaze following, and this may help us gain some insight into the evolutionary history of this trait in ourselves as well.

        The problem, of course, comes when you move from fairly well-defined, restricted behaviors like gaze following to much more complex, variable, and even poorly-defined behaviors, like “monogamy.” Here I think evolutionary psychology should fear to tread.

        The issue I have with this is basically what does it mean for a human behavior to “resemble” that of other animals? In order to draw such comparisons, don’t you have to strip culture out of the equation, since humans are the only animals with culture, particularly if we consider how thoroughly cultural human cognition is?

        I think this is an extremely important objection, and I hope you’ll never stop raising it in these discussions. I think unfortunately few biologists who are interested in human behavior seriously consider this problem, and it’s something I wrestle with all the time. To me, the key to establishing that an animal behavior really does “resemble” human behavior involves demonstrating that not only does the behavior superficially resemble human behavior, but mechanistically as well, as in the case of gaze following. That said, I think there are many cases in which the mechanistic resemblance is clear. For example, in mammals the hormone oxytocin is involved in birth, lactation, maternal care behavior, and at least in some species social bonding between adults. The role of oxytocin of all of these has been established in humans as well. While the core oxytocin system is highly conserved through evolution, the way that various other brain regions respond to oxytocin seems to vary considerably, even between closely related species, in ways that explain differences in social behavior. But even in animals, social behavior is tremendously complex and multifactorial, and differences in the oxytocin system explain only some of the variability in social behavior. Human behavior, of course, is much more complex. It would not surprise me to learn that there are cultural differences in the functioning of the oxytocin system in social behavior that are associated with different social behavioral patterns, nor would it surprise me to learn that the oxytocin system is relatively consistent among humans and the large variation in cultural expressions of social cognition is independent of oxytocin function. But in either case, to the extent that we can explain human behavior mechanistically with oxytocin, we can understand something about how it evolved by understanding how the oxytocin system evolved. And to the extent that we can’t explain human behavior with relatively well-conserved neurobiological mechanisms, we may indeed be unable to address its evolution in a serious way.

      3. “We do not have evidence of specific behaviors in pre-history outside of some inferences from the archaeological record, which is inherently incomplete.”

        Its actually worse than that, and quite a few people who deal with genetics think there is **nothing** of value in evo-psych because of it. Its cultural centric. Which is to say that it tends to ignore human adaptability, outlying cultures, where the proposed rules do not exist, or more obvious explanations, and even historical differences, all in favor of attempting to go, “Well, we see this behavior, we have literally ***no*** genetic evidence for it, but every modern human, or at least everyone that is in the cultures we bothered to look at, exhibit it, therefor it needs to be explained as an adaptation. Or rather, as a ‘genetic’ adaptation.”

        The other massive disaster is the assumption that all adaptations are genetic ones, despite the very fact that our “biggest” one is a very malleable brain, which can actually do things like simultaneously argue that monogamy is normal for humans, yet, via genetic testing, fail at it so badly that the average, across all social statuses, races, etc., for the number of kids that “are not genetically related to the man raising them.”, is 1 in 7. Pretty much 100% of everything evo-psych has claimed is in this sort of category – we do it because its cultural, and the evo-psych people presume that its part of our culture, without any evidence, because it is tied to a genetic adaptation.

        Even if correct, this doesn’t mean much. Domestication, for example, produces a *huge* range of behavioral changes, yet the number of genes needed to do it… Why? Because all of the behaviors are tied together, so flexibility as to who is “pack”, or what is “same as me”, drastically alters “all” of the linked behaviors. There is no “gene” for playing frisby, or for eating dog food, instead of hunting, there probable are genes for remaining dependent on food that is “brought to them”, or play, which doesn’t involve hunting, etc. But, those things are already there, they just override what should have shown up later in the animals behavior. Yet, dogs “can”, if not as well, develop hunting behaviors too, so its not gone, its just.. more malleable, and easier to ignore, or something not dissimilar to that.

        Humans.. can ignore entire bloody elephants in the room, and construct truly elaborate explanations for why X is true, when X isn’t even an evolved behavior, at all. But… it might have been, culturally, adaptive, at one time, when the rules we invented for ourselves where more strict, because we though they had to be.

        Problem is… that isn’t genetics. And, until you can point at the bloody gene, or cluster of genes, that actually produce an adaptation, never mind explain how and why those mutations cause someone to, say, feel the need to wear high heals, or some stupid nonsense that evo-psych has decided, this week, to babble on about, its not genetics, or science, its rampant, culturally biased, speculation. Being popular doesn’t make it genetic, unavoidable, or adaptive. Often, it just means that we haven’t had a good reason, YET, to throw the idea out.

  2. I certainly didn’t state that evo psych HAS to be contradictory to science, and I do think it can be practiced in some really good, responsible ways.

    Here are some places that talk about sexism in evo psych:
    http://disruptingdinnerparties.com/2013/05/09/whyevopsychisalmostneverscience/

    http://www.science20.com/michael_taft/why_evolutionary_psychology_pisses_you_and_why_maybe_it_shouldnt-87622

    http://feministing.com/2011/01/20/evolutionary-psychologists-women-are-less-like-to-get-themselves-raped-when-theyre-ovulating/

    1. Sorry, I might have been reading a little more bite into your article than you intended. There’s been a recent trend of knee-jerk anti-evo-psych in skeptic+feminist circles, which is certainly understandable considering how bad some of its practitioners make it look, and something I’ve even probably been guilty of too at times. Like I said, it’s a label I have a complex relationship with — sometimes I hate it and sometimes I want to defend it.

      Thanks for the additional links! I agree that a lot of evolutionary psychology has a sexism problem. It’s odd in a way, considering that one of the founders of evolutionary psychology, Leda Cosmides, is a woman, and as far as I know not particularly sexist. Some of her theory papers that helped establish the field back in the late ’80s and early ’90s are actually quite brilliant, though in my opinion suffer from the same flaws that Will raised above.

        1. Interesting. I knew about differing cultural attitudes toward menarche, but I never thought much about the other end of a woman’s childbearing years.

          (And yes, shooting the moon in Portal 2 is a Freudian thing.)

      1. And yes, I think the jury is still out on non-human primates with “long” menopause due to issues of measuring lifespans (as well as the onset of menopause) across species. Thanks for the clarification. ;)

        1. For what it’s worth, my friend Lauren Brent who studies both primates and whales also cites the “humans and two whales” fact in her article I linked above. I’m not fully versed in that literature myself so I can’t give a good citation, but last time I talked to her about it I recall she was pretty skeptical about the evidence for “true” menopause in any nonhuman primate.

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