click here for WaPo article on anthropology Footprints can provide a clue. Two sites in Laetoli, Tanzania, feature footprints of human ancestors who lived about 3.6 million years ago. They were members of the genus Australopithecus. That's the genus of “Lucy,” the 3.2 million-year-old human ancestor whose fossilized bones were discovered in Ethiopia in 1974. Our primate cousins generally continued to live in trees, existing largely on ripe fruit, with their anatomy adapted for vertical climbing and swinging from branch to branch. But long ago, some chose a different path, striking out for the frontier. They went to the ground more often and then, eventually, through many evolutionary changes they left the trees behind altogether.
To scientists who study human evolution, the Fongoli chimpanzees offer some intriguing parallels to our ancestors millions of years ago. Studies of DNA indicate that our two evolutionary branches split roughly seven million years ago. The earliest members of our branch (known as hominins) may have been chimp-like in some respects, growing fur and walking through forests on their knuckles. click here for NYT article on scientists finding by studying Chimps on Savannah of Africa That stress might have only been overcome when hominins evolved new physical adaptations. Humans have skin glands that let us sweat much more than chimpanzees, for example. The origin of our upright posture might also be intertwined with our struggle with heat.
click here to access NYT article about human migration based on DNA click here for NYT article about development of Neanderthal migrations based on DNA analysis
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