The Machiavellian theory, or the Machiavellian intelligence theory, is a social theory that hypothesizes that the increase in brain size during human evolution from primates occurred due to humans working in groups. This group work in turn causes humans and primates to think about complex issues and relationships.
Machiavelli's theory suggests that the group work that humans and primates take part in drive their brains to grow larger because they are using more of their brains. As they work in groups, they are developing more neural connections to think about complex relationships. His theory suggests that intelligence in humans is an evolved reaction to a complex environment that primates once lived in.