Wednesday, May 18, 2011

Coyne Contra Brooks

Jerry Coyne lucidly schools the NYT columnist and author of The Social Animal on the problems inherent in the group selection hypothesis (read Coyne's full article here):
In yesterday’s New York Times, Brooks writes about recent scientific “advances” in the understanding of human altruism.  And he signs on to the idea that altruism evolved by group selection.
I disagree, and see Brooks as ignorant about the true scientific issues.  If true altruism (which I define here) is indeed a trait that’s deleterious to an individual’s reproductive fitness, then it could, as Brooks envisions, evolve only by the differential survival and reproduction of groups.
That form of evolution would work like this: although genes for altruistic behavior would be constantly weeded out of populations (for altruists, by definition, sacrifice their own genetic heritage for others), those genes might survive if groups that contained higher proportions of altruists were the groups that persisted, giving rise to descendant groups more often than groups lacking altruists.  (The idea here is that groups without altruists wouldn’t flourish very well.)  That’s group selection, and it’s how Brooks sees altruism as evolving:
In his book, “The Righteous Mind,” to be published early next year, Jonathan Haidt joins Edward O. Wilson, David Sloan Wilson, and others who argue that natural selection takes place not only when individuals compete with other individuals, but also when groups compete with other groups. Both competitions are examples of the survival of the fittest, but when groups compete, it’s the cohesive, cooperative, internally altruistic groups that win and pass on their genes. The idea of “group selection” was heresy a few years ago, but there is momentum behind it now.
Let’s be clear about what biologists really know about group selection and altruism.  If true human altruism has a genetic basis, it is individually disadvantageous and could have evolved only by differential propagation of groups. That’s very unlikely, since it requires that the rate at which altruist-containing groups reproduce themselves must be high enough to counteract the substantial rate at which altruism genes disappear within groups.  It’s unlikely because groups reproduce much less often than do individuals!  Further, once a group consists entirely of altruists, any non-altruistic genes would rapidly invade it, as their carriers reap the benefits of altruism without sacrificing their reproduction.
Now if we’re talking about apparent altruism, in which individuals appear to sacrifice their reproductive interests but actually reap hidden genetic benefits, then we don’t need group selection to explain it.  As I’ve written in a longer post on this topic, kin selection (“inclusive fitness”) can do it, as can simple individual selection based on reciprocity or, simply. selection for the advantages of cooperation, as in hunting lions.

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