Strangled by Roots

Genetics and evolutionary theory predict that the biology of kinship should have biased our thoughts and emotions about relatives in several ways.

The first is the simple fact that blood relatives are likely to share genes. To the extent that minds are shaped by genomes, relatives are likely to be of like minds. Close relatives, whether raised together or apart, have been found to be correlated in intelligence, personality, tastes, and vices. The discovery of an ancestor is thus felt to reflect on the descendant, who may feel he has an explanation for the kind of person he is, and who can claim to have a dose of the ancestor's praiseworthy traits.

The similarities among blood relatives mean that they are likely to share values, and shared values can lead to easy solidarity because of what ecologists call mutualism and economists call positive externalities.