28 mars 2016

Le lac qui nous a vus naître?


Notre espèce a-t-elle vu le jour sur les rives du lac Turkana? C'est tout à fait possible, mais pas certain.

Extraits de l'article:

During the wetter times, it was an ideal place for early humans to live, and when they died it was a perfect place for their remains to fossilise. That's because Lake Turkana lies in a volcanic area, where tectonic activity can move Earth's crust and create new layers. It is within these layers that fossils from different time periods are found. 

(...) The earliest known Acheulean hand-axes were discovered near Lake Turkana in 2011. They are 1.76 million years old and were probably made by H. erectus.

(...) Lake Turkana has also helped reveal what was happening even earlier in human evolution, before the Homo genus arose.

In 1974, researchers in Ethiopia discovered a 3.2-million-year-old fossil Australopithecus afarensis, nicknamed "Lucy". Lucy's species was immediately hailed as a key contender for our direct ancestor.

(...) Her team found fossils on the western shore of lake that demonstrated there was "diversity at the age of Lucy".

In the 1990s, her team discovered a possible ancestor of Lucy's species, known as A. anamensis. This was the oldest species known from Lake Turkana, having lived about four million years ago.

A few years later, again on the west of the lake, her team discovered another new species called Kenyanthropus platyops, or "flat-faced man". This species lived 3.5 million years ago, when other members of Lucy's species also roamed.

That meant there were now several contenders for "the common ancestor" of Homo, and largely killed off the idea that humans evolved on a single line.

(...) In the summer of 2015, researchers announced the discovery of the oldest known stone tools, dating to 3.3 million years ago. It had been assumed that only Homo species could make stone tools, but the tools were older than any known Homo fossils, suggesting that older species like A. afarensis or K. platyops could also make stone tools.

(...) When you look at all these finds together, it is abundantly clear that Lake Turkana has played a pivotal role in our understanding of human evolution. But that is not to say the area was particularly significant for the early humans themselves.

Lake Turkana was simply an ideal place for fossils to be preserved, says Spoor. "That doesn't mean human evolution doesn't happen everywhere else in Africa."

For instance, many of our ancestors might have lived in rainforests, where the ground is too acidic for fossils to survive. "Absence of evidence does not mean evidence of absence," says Spoor.



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