Human evolution
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Human evolution

Anthropologists believe that our human ancestors separated as a species from the apes at least 6 to 12 million years ago. We are handicapped in attempting to determine more accurately when the split occurred and in following the evolution of humans because the fossil record is very scant. Because of the gaps in our knowledge, scientists disagree on many important questions, including which hominids were direct human ancestors and which were only cousins, what factors caused the split of hominids from the apes, and what the key factors were in shaping human evolution. New fossils are discovered frequently, however, and with each discovery we move closer to understanding the story of human evolution and the reasons that humans are so much more intelligent than any other species.


African beginnings
The split with apes is believed to have occurred in Africa. A possible environmental change that reduced forests and increased plains may have forced quadrupedal creatures (walking on all fours) to venture into the open in search of food. In time, natural selection led to bipedal motion (walking upright). Preserved footprints indicate that this occurred at least 3 million years ago. The conversion from walking on all fours to walking upright required a significant redesign of the body (longer legs, a basin-like pelvis, a curved spine, an arched foot with toes, new muscles) that would have evolved only if it resulted in major advantages.
The conversion to upright movement may eventually prove to be the key to human intelligence. Although walking upright was a handicap in escaping predators, there were substantial compensations.
The raised head allowed a greater range of vision. A larger larynx could be accommodated, allowing the development of speech. Speech, in turn, led to rational thought, a larger brain, and the development of culture. The hands were free for carrying weapons and other objects. This may have led to the opposable thumb, which allowed a precision grip rather than the power grip of the apes. The precision grip increased dexterity and was crucial to human cultural development. Thereafter, the brain, the hand, and the eye evolved somewhat together.
Natural selection favored the ability to think, reason, and anticipate events and actions, the primary advantage of humans over other species today.

Human expansion
Hominids spread from Africa into the neighboring continents of Europe and Asia. From these African roots different human species evolved, although only Homo sapiens has apparently survived to the present. Humans spread eventually across oceans to Australia perhaps 60,000 years ago and by land bridge to the Americas perhaps as early as 40,000 years ago.