It was known for centuries that man and the apes were related. At heart, their anatomy is similar, despite many superficial differences. This was the reason why Buffon and Linnaeus, in the 18th century, put them together in one family. Charles Darwin's theory of evolution says that such basic structural similarity comes from the common origin of the group. The apes and man are close relatives, and are primates: the order of mammals which includes monkeys, apes, lemurs and tarsiers.