studies of Ape DNA have explained a great deal about how the living apes evolved. The Asian apes evolved first. the line of apes leading to gibbons diverged from other apes about fifteen million years ago, whereas orangutans split off about ten million years ago. Neither are closely related to humans.
The African apes evolved more recently, between six and ten million years ago. these apes are the closest living relatives to humans, some taxonomists have even advocated placing humans and the African apes in the same zoological family, the Hominidae. chimpanzees are more closely related to humans than gorillas are, diverging from the ape line less than six million years ago. Because this split was so recent ,the genes of humans and chimpanzees have not had time to evolve many differences. humans are chimpanzees share 98.6% of their nuclear DNA, a level of genetic similarity normally found between sibling species of the same genus. a human hemoglobin molecule differs from its chimpanzee counterpart in only a single amino acid.
Gorilla DNA differs from human DA by about 2.3%. this somewhat greater genetic difference reflects the greater time since gorillas split off from the ape line, some eight million years ago. Sometime after the gorilla lineage diverged, the common ancestor of all hominids split off from the ape line to begin evolutionary journey leading to hominids. fossils of the earliest hominids, described later in the chapter, suggest that the common ancestor of the hominids was more like a chimpanzee than a gorilla. The common ancestor of apes and hominids is thought to have been an arboreal climber. Much of the subsequent evolution of hominids reflected different approaches to locomotion. Hominids became Bipedal, walking upright, while the apes evolved knuckle-walking, supporting their weight on the back sides of their fingers, monkeys by contrast use the palms of their hands.
Humans depart from apes in several areas of anatomy related to bipedal locomotion. Because humans walk on two legs, their verbal column is more curved than an ape’s and the human spinal cord exists from the bottom rather than the back of the skull. the human pelvis has become broader and more bowl-shaped, with the bones curving forward to center the weight of the body over the legs. the hip, knee, and foot have all changed proportions.
Being Bipedal, humans carry much of the body’s weight on the lower limbs, which constitute 32% to 38% of the body’s weight and are longer than the upper limbs, humans upper limbs do not bear the body’s weight and make up only 7% to 9% of human body weight. African apes walk on all fours, with the upper and lower limbs both bearing the body’s weight, in gorillas, the longer upper limbs account for fourteen percent of to sixteen percent of body weight, the somewhat shorter lower limbs for about eighteen percent.