As we had said earlier in section 13.2, Darwin had recognized that humans and the great apes shared many physical characteristics. This led him to conclude, that humans and apes descended from a common stock. Darwin's conclusions were based on the study of fossils and the physical similarities that he had observed. Now, a century later biochemical studies of proteins and the genetic material-DNA show how good his guess was, Biochemical studies show us that, as evolution proceeds and the species get differentiated, they accumulate changes in the structure of their proteins and DNA. Longer the separation time, greater the changes. These changes are expressed in terms of percent genetic distance which indicates the proportional difference between the DNA of the two species. Comparative studies of the proteins of the African apes and humans showed that chimpanzees, gorillas and humans are closely related to one another, while the Asian apes, i.e. the gibbon and orangutan were the more distant cousins of this trio .
Once the Asian and African apes were considered to be closely related and it was thought that the hominids developed from apes prior to 15 million years ago. Biochemical evidence, however, indicates that the ape-human divergence may have been much closer to five million years and that thc gorilla split off first, leaving the chimpanzees and the human-like creatures to share a common ancestor briefly before separating. Ramapithecus fossil specimen found in Asia, Europe and Africa was at one time thought to be closely related to the species of modem man. However, on the basis of biochemical evidence, it has now been shown that it cannot be considered a homonid, because it lived before the Asian apes diverged from hominids. Same is true for Sivapithecus indicus, a fine fossil specimen of which was discovered in 1980 from the foothills of the western Himalayas in Pakistan.