This article is excerpted from Steve Stewart-Williams’s latest book, The Ape that Understood the Universe. On the purposes of altruism and kin selection:

The details of Hamilton’s theory are complex, but the basic idea is fairly simple. The starting point is the observation that organisms share a larger fraction of their genes with relatives than they do with unrelated individuals. This has an important implication, namely that any gene that contributes to the development of a tendency to help one’s relatives has a better than average chance of being located as well in the recipients of that help. As a result, by helping one’s relatives to survive and reproduce, one can indirectly help to spread the genes that gave rise to that very tendency.

I’m currently reading Rory Sutherland’s Alchemy, which is full of evolutionary concepts and factoids like this, even though it’s ostensibly about marketing, bias, and decision making. Stewart-Williams’s book sounds right up there; will add it to the list.