Final answer:
The increased folding of the cerebral cortex in haplorhine primates creates more surface area, which is related to intelligence and complex social behaviors.
Step-by-step explanation:
The surface area of the cerebral cortex in primates is a measure of the brain's complexity and is related to intelligence and complex social behaviors. It is due to the increased folding of the cortical sheet, which creates more sulci and gyri. This increased surface area is seen in haplorhine primates, which include monkeys and apes. Monkeys and apes have less prognathism (protrusion of the jaw) and no tooth gap compared to other primates.