From Herbert Gintis:

Re: Giving among strangers more nurture than nature, study suggests (Oct. 13): Regarding “Giving among strangers more nurture than nature,” your report is misleading. Suppose all humans have an equal genetic capacity for altruism. Then all reported differences will be cultural. This does not mean there is no genetic component, but only that it is not heritable. For example, virtually all variation in number of hands in humans is cultural (e. g. , some societies cut off hands of thieves). Nevertheless, the number of hands in humans is genetically determined to a high degree.

Herbert Gintis
Santa Fe Institute and Central European University
Northampton, MA