Damon Clark and colleagues of the Department of Molecular Biology, Princeton University compared the relative sizes of different brain areas to total brain size. In the 10 May Nature they report that within a mammalian group the relative sizes of different brain areas are fairly constant, despite huge variations in brain size (Nature 2001, 411:189-193). For example, although the human brain is much larger than that of the lemur — a small insectivorous primate — the brain area proportions were found to be similar, and formed a group with those of other primates.