One of the main reasons why we are so interested in the other primates is that by looking at them we can obtain some ideas of what our ancestor must have been like a few millions years ago. Even though, we are not descended from any modern-type monkey or ape, our lineage does appear to have gone through stages in which we were a medium-sized, reasonably intelligent creature with good binocular vision, hands that were good at manipulation and the ability to climb trees. An evolutionary trend in primates involves the development of offspring both before and after birth and their integration into complex social systems. Another trend in primate evolution has been toward a more elaborate brain. In addition to brain size and gestation periods, social organization also demonstrates and plays an important role in primate evolution due to its complexity and hierarchy.
Brains size does matter
The larger the size of the brain the more intelligence the species, and throughout primate evolution size of primate brain has grown in size.
Most mammals display some asymmetry between the right and left side of the brain in size and morphology. According to Prince Charles Lucien Bonaparte who in 1837 divided mammals into two groups namely Educabilia and Ineducabilia. One Group, with brain surface that must be reflective of at least some intelligence, Bonaparte called Educabilia. The second and obviously inferior group he referred to as Ineducatbilia. Bonaparte's Educabilia consisted of the carnivores, ungulates, manatees and other sirenians, whales and of course primates. Educabilia was characterized by having the large portion of the brain, the cerebrum, subdivided by a crease of fissure into two or three lobelike "segments." The other group had only a single-lobed, undifferentiated cerebrum.
Not only do the large hominoids have large brains, their brains differ from those...