According to most widely acceoted theory, Man appeared on Earth 100 000 years ago in East Africa, in the current region of Somalia. The primates in this region have acquired bipedalism as a result of geological changes, resulting in a change of vegetation which became more sparse. Unable to take refuge in trees, they straightened up to anticipate any potential danger. Bipedalism is the origin of subsequent amendments to the Man in relation to primates, such as brain development ...
Without going into details of the evolution of hominids (I'm also incapable and this is not the subject), Man gradually occupied all the territories at his disposal. Regarding the settlement of America, we must go back to the last ice age ended 10 000 years ago.
To understand the origin of Man there, the researchers compared the current population of skeletons from this period. The best known are the Kennewick Man (Central America) and the Spirit Cave Man (South America) which both have similar features with the population called "Caucasian" Europeans, but show significant differences with today population.
A recent theory argued therefore that waves of "Europeans" have crossed the Bering Strait 11 000 years ago, while still frozen: there was an ice bridge between Asian and American continents, at this time -- end of ice age - ice began to recede, allowing the passage along the coast. Since then the 2 continents are completely separated.
However, more recent research have uncovered the remains of animals (wolves, bears ...) dating back 50 000 years! The men would then have crossed the "strait" well before the start of melting ice. Some assume that Man arrived in America 16 000 years ago, in full ice age. Moreover, the Kennewick Man and Spirit Cave would be more related to denizens of Japan and Hainou Man, dating from the early Asian arrivals in China 20 000 years ago.
The current population of America has similar appearance to the branch called "Mongoloid". There are thus 2 hypotheses on the evolution of Man from the beginning of the peopling of America: either the Spirit Cave Man has evolved to the current population, or it has disappeared, replaced more recently by the "Mongoloid" people from Asia.
The theories of evolution being often based on only a few skeletons (half a dozen in this case), they can often be challenged. In the future, current progress of paleontology will certainly improve our knowledge in this field.
Sources : ARTE, TMC, Odysée, various books
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