Thursday, August 16, 2012


I'm almost done with Mother Nature, by Sarah Hrdy. It is a great book, but also a very dense book- I almost want to go back and reread it immediately, since I'm sure I haven't fully assimilated all of the information in it. I probably won't do that, but I do want to write a few posts about the data and ideas it discusses.

One of the themes that has stood out for me is that of different strategies for success. This is a book primarily about biology, so success is primarily meant in the biological sense- i.e., passing on your genes. Hrdy draws from studies featuring a wide range of species, from insects to humans. Most of the studies Hrdy cites look strictly at individual reproductive success, looking out for two generations (i.e. to the existence of grandkids). However, I found myself extrapolating from the ideas to think about how different practices and behaviors might impact the success societies or groups of various sizes- it is hard not to! But for now, I want to limit my discussion to strict biological success, and will actually only talk about first generation effects, because the second generation (grandkid) effects are interesting enough that I want to write a separate post about them.

We only look like we're all headed towards the same goal
When we look at evolutionary control of traits involved in reproduction, there are many different individuals trying to optimize success, and while their interests overlap, they are not always completely in sync. The mother's overall reproductive success, for instance, may or may not coincide with one particular child's optimal success- which is a difficult thing to acknowledge as a mother, but still true. The father's reproductive success is not completely in sync with either the mother or the child, and if you add siblings things get even more complicated. There are biological traits that influence all of these various individuals' success, and these traits are therefore under selection pressure. But they all also interact, making it very difficult to identify the biological "best" way to do just about anything.

Take something as seemingly simple as the spacing of children. Biologically (i.e., without the help of chemical or other forms of birth control), this is controlled in large part by the length of time that the first child breastfeeds intensively. Many people assume that there is an optimal length for breastfeeding, or some natural limit that is hardcoded into our genes. But the evidence indicates that this is not true. The optimal length for breastfeeding depends on the type of society in which the mother and child live. How easy or hard is it for the mother to find food? Does the society provide allomothers (other adult individuals who care for children while the mothers obtain food)? Are there other suitable foods for an immature individual to eat? And so on.

Hrdy's discussion of birth spacing made me think about the common advice given to ambitious women: have one child if you must, but don't have more. The advice comes from looking at the statistics- on average, the more children a woman has, the less likely she is to stay in the workplace. This advice may be practical and accurate from a strictly statistical standpoint, but it ignores the individual variations that can make all the difference, and Hrdy's analysis of the biological research points us to what I think is the most important point of variation: the amount of support a mother has. The studies she cites show that when a group of animals, whether it be a species or just a breeding population within a species, makes more use of allomothers, the breeding interval drops. In other words, mothers who have more support and help from other adults can successfully rear more children with less time in between them. It shouldn't be surprising, but somehow a lot of people seem to be missing this point. Now, whether or not a society wants to encourage more kids per mother is another question. But both the extreme right wing who think that women must sacrifice all other interests in order to successfully reproduce and the extreme left wing who argue that women who reproduce are necessarily sacrificing their other interests are missing an important point. The story doesn't have to be about the mother and her child, all alone, and in other species, it rarely is. Other people can help, and that can make a big difference in success.

There are also different strategies for how to increase the odds your children will survive to produce their own children, and again, these different strategies are seen when comparing breeding groups within species as well as when comparing species. We often assume that the best thing a mother can do to increase her children's success is to selflessly devote herself to their care. In fact, that is not always true. Hrdy describes the research done on a mother chimp named Flo, who was initially seen as a prototypical devoted "martyr" mother, due to her patient and giving mothering style. Further research and analysis, though, showed Flo was also an extremely successful chimpanzee in terms of securing territory. And in fact, Flo's material success translated directly into greater reproductive success for her daughter. As Hrdy writes:

"A female's quest for status- her ambition, if you will- has become inseparable from her ability to keep her offspring and grand-offspring alive. Far from conflicting with maternity, such a female's "ambitious" tendencies are part and parcel of maternal success."

Particularly attentive readers may recall that I have posted that quote before. I will confess to feeling a certain affinity for Flo. If a chimpanzee can combine devoted motherhood with broader success in her society, then surely, so can I?

Unfortunately, though, I happen to live in a society that is deeply conflicted about my role as a mother, and in which many people do not recognize my approach (and Flo's) as a valid parenting strategy. My mistake, I guess.

I don't want to give too much weight to biology here. Once humans evolved consciousness, we changed the rules of the game, or at least increased their complexity. We are no longer limited to strictly biological definitions of success in life. I do not think we are even close to understanding how our ability to consciously act against our own reproductive success influences the evolution of other traits, let alone what all this means at a societal level.

But, like Hrdy, I think we can gain some insight from thinking about the biology of the system. The biological advantage from diversity is in handling bad times- maybe one of the diverse individuals has a trait that will allow survival where others will fail. I cannot help but think that diversity in mothering strategies functions in a similar way. In normal times, the outcomes from the different strategies may be almost indistinguishable. But when the rules change, some strategies may lead to thriving offspring while others lead to... well, less than thriving offspring, perhaps even to no offspring. Again, from the standpoint of an individual's life and happiness, this may be meaningless, because humans can choose to optimize different parameters. From the standpoint of a breeding group or a society, though, this can be a very big deal indeed.

Hmm. This post is getting rambly and it is getting late. I also find myself writing about societies when I said I was going to stick to individuals and strictly biological definitions of success. So perhaps I should end this, with a promise (or is it a threat?) that I will be writing future posts about other thoughts inspired by Hrdy's book. In the meantime, if you're at all inclined to think about the biology behind our societies, I cannot recommend the book enough. If you aren't, then I'll just advocate for keeping an open mind when you run across people with different parenting strategies than your own. The combination of traits in their little family unit may be very different than in yours, which may lead them to choose a different strategy. Or perhaps they're just following a different strategy because that is what helps them optimize all of the various types of success they want in life. And that diversity of approach- within reason, of course! I'm not advocating that we tolerate abuse or anything like that- may actually be a good thing for our overall society.


  1. Anonymous7:13 AM

    A related thing I've been pondering is how evolution tends to hedge its chances with all these deviant things that are unhelpful in many situations but life-saving in a few situations. Like how sickle-cell anemia is protective against malaria if you only have half the variant. There are tons of examples like that.

    As a woman with PCOS, which 10% of the female population has, I've wondered if it's evolutionarily advantagous because when times are good, a woman with PCOS is going to have many fewer children because of the way the disease interacts with weight, but when times are bad, she'll reproduce more like a normal woman. I wonder if that helped reproductive survival strategies for the tribe when there were shocks which changed good times to bad and vice versa.

    1. The malaria thing is an example of heterozygote advantage (= when one of your two copies of the gene has a "bad" mutation and that gives you an advantage, even though having both copies is harmful). There are arguments for that in cystic fibrosis and some lipid storage diseases, too. Figuring that stuff out is really interesting.

      Your PCOS theory would be something else, not sure of the official name for it. The PCOS thing could also be an example of a trait that wasn't a problem for most of evolutionary time- since times were rarely as good as they are now, calorie-wise, and is now slowly coming to equilibrium in a new environment.

      But evolution and genetics are not my strength. I find the theories fascinating, and I've studied the molecular detail of the sickle-cell anemia mutation (it is a fascinating store at the protein structure-function level, too), but I am not at all an expert on this stuff.

    2. Anonymous6:37 AM

      No, I specifically mean it in the same sense that diseases can help (provide an evolutionary advantage) under certain circumstances (in the sickle cell case, when you're in a place with malaria and you only have one half of the gene).

      Times have been good at some evolutionary points in the past (look at the CA Indians before we killed them off, for example), and in those times, women with PCOS would have had a small number of high quality children while normal women would be having a large number of children. (You don't have to be overweight for PCOS to cause infertility... but being underweight makes it less likely, while normal women have fewer kids when underweight.) Then when times hit bad, they'd have fewer mouths to spread food out to.

      I've also thought similar things about no-sleep no-fear early-gross-motor babies. It's great to have a superior baby, but some number of these must have crawled off cliffs back in the day.

    3. "I've also thought similar things about no-sleep no-fear early-gross-motor babies. It's great to have a superior baby, but some number of these must have crawled off cliffs back in the day."

      My theory is that back in the day, the probability of poor nutrition coupled with the prevalence of disease (though I realize I'm oversimplifying here, especially given the relative isolation of different groups and thus, reduced spread of germs) meant that those babies who are now "superior" were once just those who had enough energy/toughness to survive versus, you know, not.

    4. Anonymous6:21 AM


      I don't think that's likely or they wouldn't be such a small portion of the population today. There's other ways to be superior than not sleeping or being unafraid of things... and early gross-motor skills mean you're burning off calories that could have been useful for survival in a limited calorie environment.

  2. Do you remember a big international study that came out ~2005 that discovered that the .best. predictor of whether a wife will have a second child is how much housework and childcare her husband does? It trumps everything else, including money, class, education and employment.

    1. No, I missed that one. But it makes complete sense to me!

  3. Keep "an open mind when you run across people with different parenting strategies than your own."

    AMEN! That belongs on a bumper sticker. And Flo rocks.

  4. Heya Cloud,
    I am a regular reader of yours, though a rare commenter. This is like the 3 rd one...
    Got to say there is something nice that most of your blogs leave me with!

    Your biological success made me think of how happy my grandma would have felt whe she saw my son!! I could see her so much more happy since his birth.

    About your point about the modern way of living, changing the meaning of success, I don't think it really has. The need to have progeny is possibly coded into us. And, those who defy that and still are (truly) happy would have done the same thing even in primitive way of living.

    Makes me wonder what the achievement of our luxurious life is. (in comparison with forest dwellers).

    Awaiting your next in series!


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