 The very idea that biological altruism can come about through natural selection may initially seem puzzling. One way of characterizing natural selection, after all, is in terms of “selfish genes”: natural selection occurs when a variant of a gene (an allele) at a given locus tends to cause a modification of a bodily or behavioral trait (a phenotypic trait) in a way that, in the overall environment, tends to cause that variant of the gene to increase its relative frequency in the next generation; this then increases the representation of the associated trait modification as well. Typically this happens when the phenotypic modification is one that causes the organism to have greater reproductive success: if, in the overall context, allele A causes its carrier to have a trait T that causes the organism to have more offspring than other organisms in the population who carry rival allele A* and display alternative trait T*, then A will be inherited and carried by more organisms in succeeding generations; and that means that T will likewise be displayed by more organisms (Dawkins, 1989). But how do we get from “selfish genes” increasing their representation in the gene pool, via improving the reproductive success of their carriers, to such things as cooperation and biological altruism? It turns out there are many ways.