J. M. Burkart and C. P. van Schaik
Thornton & McAuliffe (2015) recently questioned the cooperative breeding hypothesis (CBH), i.e. that cooperative breeding has a variety of socio-cognitive consequences. However, the CBH is not merely a modified version of the social brain hypothesis as implied by Thornton & McAuliffe, since it does not claim that a species would have to be particularly smart to engage in cooperative breeding. Rather, the CBH posits that the immediate tasks associated with extensive allomaternal care require motivational proximate mechanisms, such as increased social tolerance and proactive prosociality, which, as a side effect also can facilitate performance in socio-cognitive tasks. Eventually, over evolutionary times this constellation may also, under specific conditions, facilitate increases in brain size. We first clarify these conceptual issues and then address the criticism of the empirical evidence. We conclude that the evidence for the CBH is strong for primates, and future work on other lineages will reveal its generality.