 A second example of a more pragmatic, problem-driven invocation of cultural selection can be found in the ‘Tribal Social Instincts’ hypothesis. As Darwin (1877, 134) noted, humans are regularly moved to act in ways that benefit others, even when those others are not members of extended families. He suggested that we are moved by sympathy for others, and that the ultimate explanation for why we have such fellow-feeling can be explained as a result of a process of selection, albeit one that acts at the level of what he calls ‘tribes’. This explanation has been updated across a long series of publications by Richerson, Boyd and others, who also aim to explain the very widespread tendencies of modern humans to share valuable resources across broad social networks (e.g. Richerson and Boyd 2005, Richerson et al. 2016). Their view is that the resources of more mainstream evolutionary theory are not up to this explanatory task. Kin selection is insufficient, they say, because humans regularly share with people outside their immediate family groups. Moreover, they take the view that the Pleistocene social groups in which (they believe) these sharing behaviours evolved were probably too large for reciprocal altruism to explain their emergence. Their favoured explanatory hypothesis is a complex one, involving interaction between what they call ‘cultural group selection’ and natural selection acting on genetic variation: “Selection on tribes can account for the innate foundation of our social psychology via the process of gene-culture coevolution” (Richerson and Boyd 2005).