Prosociality in large human groups more likely due to culture than to genetics.

Bell et al. think about whether human prosocial behaviors such as food sharing, taxation, and warfare - nearly completely absent in other vertebrates - are more plausibly explained as arising from to cultural or genetic selection during competition among large groups. They use the term "group-level selection" to refer to the scenario in which groups differ in the frequency of individuals who are willing to sacrifice their own labor, time, or safety in ways that promote the competitive ability of the residential group, so that over time groups with higher frequencies of such “altruists” may tend to replace groups with fewer. A key point is that:

Selection for culturally-prescribed altruists occurs through the same process as for genes: groups of altruists leave more daughter societies. However, one advantage that cultural variation has over genetic is that it does not require violent inter-group competition, nor group extinctions. If failed groups were incorporated routinely into successful ones, conformist transmission and other forms of resocialization of failed groups can lead to effective cultural selection on groups even though such a pattern will generate rates of migration that keep genetic F_ST (a measure of genetic differentiation between populations) very low between neighbors. Thus selection on culture can be powerful precisely when genetic selection at the group level is weakest.

The meat of the article is formal calculation using the Price equation (don't ask...) that suggests much greater scope for cultural rather than genetic group-level selection in allowing altruism to arise.