Figure 1.

Alternative explanations for the evolution of large brains in primates. Explanations differ in whether their central claim is (a) about ontogenetic or energetic constraints, versus ecological or social processes, (b) whether they view food, mating or predation as the rate-limiting process for fitness, and (c) whether they view the fitness benefits from large brains as being direct (individual-level benefits) or indirect (arising out of social processes). Principal references: ^a[22–24], ^b[20,21], ^c[22,25–27], ^d[28–33], ^e[25], ^f[34], ^g[17,18,35], ^h[17,36,37], ⁱ[38], ^j[39], ^k[40] and ^l[5,6,8,41,42].