Although they belong to the same order, primate, the physical differences between man and the present-day apes are so great that we cannot imagine a direct line of descent from one to the other. The evolutionary path taken by the apes does not lead to man. It is a detour. Like the lemur and the monkey, the ape occupies a side branch on our family tree. Our direct ancestor must have lived before the four present varieties of ape ever came on the scene.
The ape's cranial capacity is between 400 and 500 cc; man's is 1450 cc, more than double. An Ape's foramen magnum (the hole through which the spinal cord goes in to join the brainstem) is located toward the back of the skull; man's foramen magnum is at the center of the bottom of the skull, giving him a balanced posture of the head and, hence, a better view and perspective of his surroundings. Man has longer legs, shorter arms, and a basin-shaped pelvis. Although both have hands, fingers and flat fingernails, man's hand has a strong finger opposing the other four, called thumb, giving him dexterity when manipulating tools and weapons, such as a spear or ax, and accuracy at throwing stones.
The ape's backbone forms a single arch; man's is an S curve. Its jaws are U-shaped; ours, more gently curved, look like horseshoes. The ape's canine teeth are exceptionally long; our canine teeth are about the same height as the rest of the teeth. All apes have two spaces in the row of upper teeth into which the long lower canines fit when the jaws are closed. Whereas the foot of the ape has been modified to so serve as an additional hand with which to hang onto a tree branch, the foot of man has become specialized for walking, developing an arch in the sole. Although the ape can stand and walk (awkwardly), still it is not a biped, that is, a creature, like us, that goes about on two legs at ease all the time. The ape is a brachiator, most at ease when it brachiates, or swings, through the trees hand over hand, with its hands adapted for such acrobatics. Our hand, since it is not used for locomation, has become primarily a highly specialized grasping organ.