Kinship, need, and the distribution of altruism.

The optimal distribution of investment in kin cannot be determined solely on the basis of knowledge of genetic relatedness. The distribution will be affected by the fact that altruists are likely to encounter diminishing returns on their investments in kin. Returns to altruism will also vary because of phenotypic variation among recipients. Differences in fitness conversion efficiencies may outweigh relatedness considerations so that a distant relative may be more valuable than a close relative. Or else, if all kin are superefficient at converting investment into fitness, an even distribution of investment among kin may be optimal irrespective of differences in relatedness. It is necessary to ascertain whether the principal consequence of investment results in increased fecundity or increased survivorship of recipients because the optimal distribution of investment may differ considerably in each case. -Authors