Anthropoid primates today include New World monkeys, Old World monkeys, great apes and humans. Anthropoids differ substantially from other primates on anatomical, behavioral and ecological levels. Anthropoids have larger brains, generally live in larger groups and are more socially complex; all anthropoids, with the exception of the douroucouli, are diurnal, and all, with the exception of humans, move in forests or on the ground mainly by quadrupedal walking rather than by saluting from a vertical support. Humans differ from other anthropoids mainly in two particular adaptations: bipedalism and their large brains, but other fundamental aspects of our anatomy are inherited from our anthropoid ancestors.
The marked differences between anthropoids and other primates, both present and fossil, have made the search for the origin of anthropoids one of the oldest and most controversial issues in Paleoanthropology. Traditionally, paleontologists have placed the origin of the anthropoid lineage in Africa. Since anthropoids are usually considered more evolved than other primates, many who have studied them have assumed that they took a long time to evolve. Today's anthropoids are larger than lemurs and tarsiers, and many have suggested a trend in early anthropoids towards increased body mass. As a result, some scientists have written that anthropoids must have evolved from the largest of the Eocene primates, lemur-like adapiforms such as the recent (and largely discredited) German fossil Darwinius.
