In defense of evolutionary psychology, part 3: Hamilton’s rule and reciprocal altruism

Hume once said that “A man naturally loves his children better than his nephews, his nephews better than his cousins, his cousins better than strangers, where every thing else is equal.” When I first found this quote from Hume, I was quite impressed, because it anticipates an idea that wouldn’t be formulated until roughly 200 years after Hume lived: Hamilton’s rule.

I’ve been meaning to restart my series defending evolutionary psychology for some time (see part 1 and part 2). Initially, I was thinking part 3 would be about sex differences in behavior, but ever since I saw this post by Stephanie Zvan, I’ve wanted to respond to it and the post at another site it was promoting, “Altruism — can we do good just for the sake of it, after all?” by Anne Buchanan. I’ll quoting Buchanan’s explanation of Hamilton’s rule:

Evolutionary biologist, William Hamilton, formalized the idea in an equation published in 1975, in what came to be called inclusive fitness:

      rb > c


      is “degree of relatedness”,
      is the reproductive benefit to the recipient of the altruistic behavior, and
      is the reproductive cost to the altruist.

In very basic terms, you and your sib, parent, or child share half your genes.  This is on average and it’s statistical.  You can’t say in advance which genetic variants you’ll share, just that overall it’ll be half of them.  That’s because everyone gets half their genes from their father, half from their mother.   So, if you do something for your sib that puts you at risk, say, of having one of your own children, but your assistance leads your sib to have at least 2 children s/he that wouldn’t have had without your help, then the genetic variants you carry will, on average, proliferate–via your sib’s children who will carry those variants.

This is exactly right. It’s worth explaining that we share 50% of our genes with our siblings, parents, and offspring; 25% of our genes with our aunts, uncles, nieces, and nephews; and 12.5% (1/8th) of our genes with our cousins. And the key thing here is that this number is the same as the probability of sharing any one gene. So a relative-helping gene will be promoting a copy of itself 1 out of every 2 times it helps an immediate relative, 1 out of every 4 times it helps a niece, nephew, etc., and 1 out of every 8 times it helps a cousin.

I hope that makes sense. If not, Richard Dawkins has a brilliant explanation of Hamilton’s rule starting on p. 90 of The Selfish Gene, and this is one of several reasons I recommend everyone read the book. Though his explanation is longer than the one I just gave, so I won’t try to quote it; read it for yourselves.

I should mention that Buchanan describe’s Hamilton’s rule as a formalization of the idea that “altruism is selfish after all.” It can be tempting to think that way, but I agree with Hume (at least I think he also said this, can someone find the quote for me?) that concern for family is not part of what we normally mean by “selfishness.” Nor, to update Hume, is promoting one’s genes what we normally mean by “selfishness.”

Now for Buchanan’s argument that Hamilton’s rule isn’t relevant to explaining human behavior:

Under these conditions, if a variant in question leads you to this helpful rescuing behavior, the variant will (statistically) proliferate, because helping your sib to have more children than you give up will increase the frequency of those helping-variants in the next generation.  Likewise, you share 1/8 of your variants with your cousins, so to give up a child of your own by helping your cousin, that cousin would have to have at least 8 more children than without your help.  That’s what Haldane meant.  This may make little sense in slow reproducers like humans, but could actually work, in principle at least, in fast reproducers who produce hundreds or thousands of offspring–like ants.

So, Hamilton’s rule seemed to explain why vampire bats feed each other, why bees will sting, and die, to defend the hive, and why Ken dove into a pool to save a drowning stranger years ago.  It even came to explain things that had nothing to do with altruism, such as homosexuality, which could evolve because homosexuals cared for the offspring of their kin, thus perpetuating their own genes even if they themselves didn’t reproduce.

This would seem to show clearly that, by itself, Hamilton’s rule simply cannot explain human (or even primate) sociality.  In all human societies people routinely help their cousins and other more lineally distant relatives.  But primates simply cannot have 8 or more additional children as a result of being helped.

This is a mistake. Thinking in terms of whole offspring may be useful for introducing Hamilton’s rule, but it’s not true that sacrificing one offspring is the minimum cost of actions we take to benefit relatives. For example: a stone-age hunter kills a large animal, and he and his immediate family eat as much of it as they possibly can. But there are leftovers, and without refrigeration or even salt, it will rot before the immediate family can eat any more.

Hamilton’s rule suggests that in this situation, the hunter will give the meat away to his more distant relatives. Because the meat will rot otherwise and be of no use to the hunter, the cost (“c”) is basically zero. Because of that, even a slight positive benefit to the distant relatives, a slight positive increase in their reproductive chances, will be a “b” large enough to make the action satisfy Hamilton’s rule.

Or, to use the historical example that gave us the word “nepotism,” if you’re a medieval Pope, handing out church offices to your nephews might cost you very little if the people surrounding you in the Catholic hierarchy don’t care that you do it. If you’re following your vows of chastity (though not all historical Popes did so), the reproductive cost to you might be zero. So the reproductive benefit to your nephew doesn’t need to be very large to satisfy Hamilton’s rule.

Back to Buchanan:

So those who have thought about this have had to devise various escape-value explanations to preserve the essence of Hamilton’s rule; one is ‘generalized reciprocity’ the idea that I may help you because some day you may return the favor.  But with such escape valves, and the complexity of society, it should long ago have been clear that all bets are off.

Stephanie comments on this in her own blog post:

In other words, in order to tweak the model to accommodate actual, observed social behavior in primates, it becomes so squishy that it loses its predictive power. That, of course, is where it stops being science. It certainly isn’t impossible that someone will come along and add complexity to the basic model in a way that allows it to become predictive again, but the idea isn’t at that point at the moment.

First of all, Buchanan is wrong that the idea of reciprocity was added as an “escape valve” to avoid the “cannot have 8 or more additional children” probablem, because that “probem” isn’t one. But it’s also not true that taking reciprocity into account makes the model “squishy.” It very clearly cannot explain any altruism whatsoever; it wouldn’t for example explain a willingness to be repeatedly taken advantage of by non-relatives. And it wouldn’t change the fact that we should expect animals to be more altruistic towards relatives than towards non-relatives. (By the way, The Selfish Gene is also excellent on explaining reciprocal altruism.)

I’m going to pass over some of her complaints about the fact that E. O. Wilson has changed his mind on some issues, as well as the question of whether haploidity explains eusociality in insects. Even if Buchanan had a point about those things, it wouldn’t settle more general issues about the evolution of altruism (though the eusociality issue is interesting, and I may try to write about it later). Instead, I want to deal with this part from the end of the essay:

Why is the demise of Hamilton’s rule as Gospel such a big deal?  Because it shouldn’t have been a Big Deal in the first place.  And yet why should we care what Wilson says this time around anyway?

The problem with all of this is the desire or even deep hunger, to find some precise, competition-centered pat explanation for observations about life. Anything that looks organized is assumed to be due to systematic, force-like Darwinian competition.  Even group selection, which Wilson is now advocating, is a simplistic notion, that orthodox Darwinians cannot accept because it doesn’t work strictly at the level of the individual which they insist, for some good reasons, it must, since it is only individuals who carry genes and either do or don’t reproduce.  From that point of view, everything that looks cooperative simply must have arisen and/or work strictly to the advantage of the individual.  Or, to be even more precise, it has to work at the level of individual genes.  It has to, to seem like real science!

This is a reverse kind of logic.  If you view the world as horribly selfish and cruel, then of course anything can be explained by selfishness.  On the other hand, if you see cooperation as being important, you can argue that things good for a group advance even if genetically they arise only in one member of the group.  You can argue that over time, the kindliness genes will spread and advance: each kindliness mutation will add to the group’s success.  Even those without kindliness variants will do well, but they won’t out-do their nicer peers.  Arch Darwinists who seem to be convinced the world is full of cheaters (does this imply that they know they’re cheaters themselves, and is some sort of tacit confession?), will always devise (again post hoc) reasons why kindness for unselfish reasons will never win.  Or they will always be able to find reasons why kindness is just competition in disguise.

Again, first of all Buchanan is wrong about the demise of Hamilton’s rule. But the reason theories like kin altruism and reciprocal altruism have gained widespread accepted in the scientific community is not because of a mysterious “deep hunger” to find competition-centered explanations. It’s because the alternative explanations don’t work (and these theories do).

If there ever were a population of organisms with genes for behaving altruistically towards non-relatives, regardless of whether the non-relatives responded in kind, it should be easy to see that those genes could be quickly replaced by variants for behaving more selfishly, as long as the variants were able to arise in the first place. One strategy would be to benefit from other’s altruism while displaying none of it yourself. Though in many situations, a better strategy might be to go tit for tat, helping those who’ve helped you in the past and not helping those who’ve refuse to do so.

Can we, as the title of Buchanan’s post suggests, do good just for the sake of it? Perhaps in a sense. But not in any sense that helps with understanding the evolution of animal behavior (human behavior included), at least not until someone explains how “good just for the sake if it” could impact gene frequencies. By the way, if you get thinking about group selection here, the consensus seems to be that it doesn’t work. I may devote post to the subject in the future but for how, I recommend Steven Pinker (actually a great article on the evolution of altruism in general) and this this more narrowly focused piece by Eliezer Yudkowsky.

Final point: the last of the paragraphs I’ve quoted is one bit of data that confirms my general impression that discomfort with evolutionary psychology tends to be driven not by the science, but by confused moral objections to the ideas. Buchanan doesn’t exactly say that the ideas she criticizes are immoral, but she does speculate that the reason people hold them is because they’re bad people. To which I reply: evolutionary psychologists may not behave very altruistically towards non-relatives when they don’t stand to gain anything in return, but then neither does the vast majority of the rest of humanity.

Case in point: in the past, I’ve made efforts to donate money to charities that will actually help other people the most with that money, and encouraged other people to do the same. And I intend to do more of that in the future. But there are plenty of petty things I spend my money on much more readily on than that. And I haven’t empited my savings to save strangers from malaria, whereas if my little brother desperately needed money for a life-saving medical treatment, it would be an easy decision to empty my savings for his sake. And yet my tendencies in that regard are not especially selfish or nepotistic for a Homo sapiens.

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