In "The Prince," Machiavelli set out his manifesto of duplicity and deception. His name stands for cunning, for forming alliances with those in power. The theory of Machiavellian Intelligence proposes that with the advent of social interaction, the advantage gained by manipulating others was the driving force behind the evolution of the primate brain. The theory receives support today from a paper in Nature.

Mammals, we all know, have big brains. Brain size increases with body size, so as you move from mice to monkeys, brain size gets proportionally bigger, like moving through a Russian doll set from the inside out. But Damon Clark and colleagues at Princeton University's departments of Molecular Biology and Physics have now found that the Russian doll analogy doesn't describe the whole picture.

If you look at brain size within a group of mammals, such as insectivores, the analogy holds: Brain size changes in proportion to body size, and the various parts of the brain, like the cortex and the cerebellum, stay the same size in proportion to each other. However, the proportions of different parts of the brain to the total brain size change in different groups of mammals. In other words, each layer of the "doll" is not just a bigger version of the last but is sometimes architecturally different.