Asymmetries of Relatedness

For five years—and probably more—I've been tinkering with an idea. I think it may be the most interesting one I've ever had, and I'm overjoyed to say that it's just been published in fine form in the Proceedings of the Royal Society B: Biological Sciences.

(Don't worry: there's a video at the bottom of this page that will make sense of it, I promise. Feel free to skip to the end if you'd rather not wait.)

In social evolution, we usually consider two parties: the actor, who performs a behavior (like altruism or spite), and the recipient, who feels its effects. From Peter Taylor's work, however, I had learned that others beyond this primary actor-recipient pair also influence social evolution. Dubbed the "neighborhood," these other individuals have to compete with the surfeit or dearth of offspring that interactions between the actor and recipient will usually breed. Taylor showed that, since one's neighbors are also often one's relatives, this secondary layer of competition can sometimes cancel out the genetic benefits of the primary interaction. 

David Queller took Taylor's argument and made something beautiful out of it. He suggested that, with some simple rearrangements, we can think about genetic relatedness as a statement not about the actor and recipient's probability of sharing copies of the gene causing the behavior, but about their probability of sharing the same gene above and beyond chance. And chance, in Queller's formulation, is dictated by the frequency of the gene in the neighborhood. 

Once I understood this, I realized that there was something truly new to be said about the evolution of social behavior: that individuals might regulate how nice or nasty they are to a partner based on both their partner's genotype and the genotypes in their neighborhood. This implies that individuals with common genotypes might behave differently from those with rare ones, and so the concept of "asymmetrical relatedness" was born. 

With Lisa DeBruine and Ben Jones, I published a sketch of this idea in a book chapter. But, with lots of chalk and ink and pixel dust, Peter Taylor and I managed to turn it into something much more rigorous and powerful. As promised, this video will explain the origin and effects of asymmetries of relatedness. I hope you find the concept as interesting as I do. 

Cover image by G. Mützel