62:2.1

A little more than one million years ago the Mesopotamian dawn mammals, the direct descendants of the North American lemur type of placental mammal, suddenly appeared. They were active little creatures, almost three feet tall; and while they did not habitually walk on their hind legs, they could easily stand erect. They were hairy and agile and chattered in monkeylike fashion, but unlike the simian tribes, they were flesh eaters. They had a primitive opposable thumb as well as a highly useful grasping big toe. From this point onward the prehuman species successively developed the opposable thumb while they progressively lost the grasping power of the great toe. The later ape tribes retained the grasping big toe but never developed the human type of thumb.