Is Kin Selection Dead?

I went to a nice seminar today hosted by the UCLA Center for Behavior, Evolution and Culture. Peter Nonacs gave a talk titled Is Kin Selection Dead and Is It Time to Move On in Understanding the Evolution of Cooperation?. E.O. Wilson has been publishing a critique of kin selection for years, but his most recent article in Nature has generated a lot of recent activity. In particular, this response’s author list reads like a “who’s who” of eminent evolutionary biologists.

Peter spent the first part of his seminar introducing the debate, which, as he puts it, centers on the difference between an “actors-view” perspective on the evolution of cooperation or a “genes-view” perspective on the evolution of cooperation. Traditional kin-selection theory takes an actors-view perspective which focuses on evolution at the level of the individual or indirect benefits to the individual through indirect fitness. The “genes-view” perspective is more of a multi-level selection argument a la David Sloan Wilson. In the genes-view perspective you don’t need to take relatedness into account to explain the evolution of cooperation. The math is a bit beyond me, but Peter summarized it briefly by saying that the central observation is that individuals breed better in groups than in solitary arrangements and you don’t need to take relatedness into account to explain group formation. I believe you do need to get some level of population structure across groups to get the evolution of cooperation in the multi-level selection framework – so in a way, even in multi-level selection theory you do need to take genetic similarity into account. Some have suggested that the differences between the two groups is a matter of semantics.  I think that Peter thinks that the differences between the groups are real, but that each framework may be at times useful.

Or at other times, perhaps neither framework works well.  Peter spent the second half of his talk introducing the concept of social heterosis. It’s a very interesting topic, but I am not quite sure how well it fits in the kin selection debate. Peter claims that social heterosis provides a pathway to cooperation that does not require the clustering of related individuals. Heterosis is another term for hybrid vigor – in many breeding experiments, outcrossing leads to healthier offspring than highly inbred individuals. Inbreeding typically leads to the expression of deleterious recessive alleles. If you know a couple of folks with pets, you may be aware that owning a mutt will generally lead to a healthier, long-lived animal than owning a “pure-bred”, which are often susceptible to diseases and genetic abnormalities. Social heterosis applies the same logic of the reproduction of an individual, but instead applies it at the level of a group. In 2007 and 2008, Peter and his PhD student Karen Kapheim, published a series of papers that models the social heterosis mechanism. The model estimates a within-group fitness benefit and an across-group fitness benefit. Across-group fitness benefits are primarily determined by the genetic diversity of the group composition and increasing group diversity leads to higher fitness. Peter has a nice slide illustrating the benefits of diversity which shows a photograph of Karen and another grad student, Brittany Enzmann picking fruit in an orchard. Karen is tall and picks the fruit near the tops of the trees while Brittany is short and picks the fruit from the bottom. If they were the same height, they would not be able to exploit the resources from the environment as efficiently. As it is the NBA playoffs right now, I thought of another illustrative example. A basketball team composed of all point guards or all centers would not do as well as a basketball team that had players that specialized in the different rebounding, shooting, and dribbling skills. I see the social heterosis concept as a potential answer to the question “what maintains genetic diversity” in some traits, but missed how it provides a solution to the central differences between the kin-selection and the multi-level selection viewpoints. I am not sure Peter claims that it is a potential solution, but is rather another model of group-trait evolution.

I need to read Peter and Karen’s paper a little more closely to look at their potential case studies, but I wonder whether the social heterosis mechanism is widespread. I am especially interested in whether there are any natural examples of group formation where close relatives are excluded and foreign individuals are readily incorporated. There are many examples of sex-biased dispersal to prevent inbreeding, but the other sex typically remains around.  In cooperatively breeding groups, aren’t helpers almost always relatives? It seems to me that kin-structured groups are prevalent in nature – primarily due to philopatry. It will be interesting to see if the social heterosis concept takes off, but it is clear the the evolution of cooperation is a hot topic in the community right now.