David Sherry also stressed the need to use comparative studies. He illustrated this through research into spatial memory in both birds and mammals. Food sharing birds have an increased hippocampus and related brain areas. Rodents show sex differences in the same brain areas. Polygenous male rats, who need to find females in the environment, having the larger hippocampus.
Humans also show sex differences in spatial ability.
A comparative approach suggests that sex differences in human spatial ability are sex specific adaptations and may provide tools for determining the adaptive significance of sex differences in human cognition. There is one problem with Sherry's sex differences in cognition. Human culture has often restricted female experiences, therefore any differences may not show the adaptive differences in human cognition only differences imposed in the very recent past. Steven Pinker focused as one would expect exclusively on language evolution. His approach too embraced the cross cultural and complementary approach to cognitive research and the social aspects of cognition.