Time and Relatedness in Microbes and Humans
The concept of relatedness plays a central role in models of the evolution of cooperation. We tend to think of relatedness as arising through shared ancestry (i.e. kinship), but it can also arise by other means, and in microbes there is a particularly interesting and under-explored source of relatedness: horizontal gene transfer. When genes are transmitted horizontally between adjacent microbes, those microbes come to resemble each other genetically in ways they did not before. I ask: (i) what implications does this hold for the concept of relatedness?, and (ii) can these lessons from the microbial case be used to inform models of cultural evolution, where horizontal transmission (of beliefs, values and skills, through social learning) plays a crucial role? Drawing on my book The Philosophy of Social Evolution (2017, OUP), I argue that horizontal gene transfer pushes us to redefine relatedness in diachronic, rather than synchronic terms, and that a diachronic concept of relatedness may be useful for understanding cultural evolution.