 Needless to say, this work is contentious. It is possible to challenge the claims made about the innateness of the social psychological dispositions in question, the characterisation of likely Pleistocene social groups, the inability of more traditional evolutionary resources to explain our altruistic tendencies, and so forth (see Birch 2018). Such challenges are inevitable when a hypothesis is as ambitious as this one, and when it draws on such a variety of supporting sources of data. There are also conceptual concerns. A recent paper lists three different forms of cultural group selection, of which straightforward competition between groups is just one variant (Richerson et al. 2016). The authors also offer selective imitation (by individuals) of individuals in successful groups, and selective migration (by individuals) into successful groups, as two further types of cultural group selection. These are indeed additional ways by which behavioural traits that are of benefit to a group can increase in frequency in a larger population of groups. However, in the second two cases, trait frequencies are increased simply by individuals’ attraction to traits that they regard as bestowing collective benefits. Because of this, thinking of them as forms of group selection may introduce confusion (see also Morin 2016). Regardless of these worries, it is clear that the cultural group selection explanation for forms of altruistic behaviour marks a significant effort to synthesise theory and evidence across a wide set of domains.