Table 1.

Comparison of the main hypotheses for brain evolution against the five key explanatory criteria.

	hypothesis can explaina
criteria	instrumental	MIH	CIH	VIH	SH	SBH
(i) primates have larger brains that other animals	X	√	X	(√)	(√)	√
(ii) quantitative variation in primate brain size	√	(√)	X	X	X	√
(iii) brain size correlates with group size in primates	X	X	X	X	X	√
(iv) primate sociality is complex (bonded)	X	X	X	X	(√)	√
(v) pairbonded non-primates have large brains	X	X	X	X	√	√
(vi) some primates are more innovative technically	√	X	√	X	X	√

^a√, the hypothesis provides an explanation for the phenomenon indicated; X, hypothesis is unable to account for the phenomenon. Parentheses indicate cases where the evidence is arguable.