EVOLUTION BEFORE THE HOMO GENUS It is sometimes helpful to understand how evolution proceeded prior to the arrival of the Homo genus. Primates on earth have existed for 65 million years. There are several animal species that have been termed the first primates”. These were likely the Plesiadapis from North America and the Archicebus from China, although there were others in Eurasia. They evolved into several life forms, some of which became modern great apes. The catarrhines or the genus Catarrhini were early ancestors to monkeys that liked in Kenya, arriving at about 24 million years ago. The archaic species had tails and were not bipedal. About 22 million years ago, in the early Miocene period, there were many different catarrhines that lived in trees in East Africa. There were many descendants of these species. The earliest Old-World Monkeys were found to date back 20 million years ago, leading to the ape lineage, which began about 13 million years ago. Most lived in tropical and sub-tropical environments in places as far north as Spain and Austria. Gibbons have no fossil record for their origins but these were the first divergence of the great apes. The Orangutans followed these. There were those in the Nakalipithecus genus in Kenya found to be the last common ancestor for gorillas, chimpanzees, and Homo sapiens. The first gorillas split off about 4 to 8 million years ago and the chimpanzees followed. There is little fossil record for these early chimpanzees and gorillas, partly because the climate tends to dissolve bone. There is little fossil record also for the divergence of hominins from the gorilla and chimpanzee lineages, with the early human lineage being the Sahelanthropus and Orrorin. These were followed by the Ardipithecus genus. It is argued that these primates engaged in selfdomestication because of behavioral adaptations occurring in evolution at the time. Australopithecus existed in East Africa around 4 million years ago but became extinct about 2 million years ago. There were several species that have been discovered, as well as some subspecies. At least one species, referred to as Little Foot, had an opposable big toe, indicating that the species was probably a good climber. Because of predation, it is thought the nested in trees.
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