Question

According to recent studies, if the __________ of the primate brain has a larger than average volume, the more likely that primate is to be sneaky.

Answer 1

I think the blank refers to 80% of the mass.  The theory called Machievellian Intelligence Theory, it states that the larger the brain of a primate the higher social skills it possesses. Aside from the complex skills, it also possesses better cognitive skills compared to other mammals.