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The primates are one of the earliest of the mammal groups to evolve after the mass extinction that took place 65 mya. They appear to have arisen first in what are now North America and Europe, but the success of their adaptations allowed them to radiate over the Old World and back into the New World after the hemispheres separated. About 23 mya, primitive apes first appeared, and from one group of African apes our family, Hominidae, branched off around 5 mya or earlier. The habitual bipedalism that marks our family seems to have evolved in response to a fluctuating environment of both forest and open plains. These earliest ancestors were essentially small, bipedal apes. About 3 mya, a further climate change led to two new hominid adaptive responses. One gave rise to another small, bipedal apelike form with massive chewing bones and muscles adapted to the tough, gritty vegetation of the plains. The other response was the evolution of larger-brained hominids. These hominids, the first members of genus Homo, survived by inventing stone tools, which, among other things, allowed them to scavenge the meat of the vast herds of grass eaters. From this adaptive base, the evolution of our genus accelerated. The Homo erectus stage, with its basically modern bodies and even larger brains, migrated all over the Old World, encountering the climatic changes of the Pleistocene, improving stone tool manufacture, and, at least in some areas, taming fire. Modern-sized brains were reached 750,000 ya, although crania retained some primitive features. These archaic Homo sapiens, first seen in Africa and southern Europe, also spread across the Old World, and exhibited such typically human behaviors as burial of the dead and care of the elderly and infirm. The Neandertals are one of the best-known forms of this stage. The anatomically modern Homo sapiens stage, first appearing in Africa around 300,000 ya, is characterized by further advances in toolmaking, the clear practice of big-game hunting, and the first expressions of art. Members of this stage entered Australia and nearby islands and reached the New World. Farming, cities, writing, and all the cultural features we associate with modern humanity follow. |