This is due to the reduction of the olfactory region of the brain and the reliance on their sense of smell. Other parts of the primate brain have become larger through evolution in order to accommodate social behaviors, sight and eye-hand coordination. The result is an increase in the overall brain-to-body ratio which is larger than other mammals. Primates also have eyes that are arranged in a forward facing position to give them stereoscopic vision; thereby enhancing depth perception.
The physiology of female primates has evolved to be able to support a longer gestational period than most other mammals their size. Humans have a gestational period of about 280 days which is comparable to chimps, orangutans and gorillas. The smaller primates such as the lemurs and baboons have somewhat shorter gestational periods. Primates also have a longer lifespan than other mammals their size.
Finally, primates are social animals and they spend a great amount of time in social interactions. One of these interactions is called “social grooming”. This is an activity where primates will take turns cleaning the