Les scientifiques ont découvert la preuve solide que les humains anciens n'étaient pas aussi séparés que nous le pensions autrefois—ils se mélangeaient et se mêlaient ! En étudiant l'ADN des fossiles, les chercheurs ont trouvé que nos ancêtres, Homo sapiens, avaient des enfants avec les Néandertaliens et un autre groupe appelé Denisoviens. Ce mélange a laissé des traces génétiques qui existent toujours chez les humains modernes aujourd'hui, comme certains traits du système immunitaire. Certaines personnes portent même de l'ADN lié aux Denisoviens qui les aident à s'adapter aux hautes altitudes. C'est comme une réunion de famille préhistorique, montrant à quel point les premiers groupes humains étaient interconnectés. Ces découvertes réécrivent l'histoire de l'évolution humaine, prouvant qu'elle n'était pas linéaire mais plutôt comme un réseau de relations ! Animation créée par Sympa.
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FunTranscript
00:00There could have been more human species in history than we thought.
00:06In an eastern region of China, scientists discovered the remains of a human being who lived about 300,000 years ago.
00:16They found a jaw and parts of a skull.
00:19They carefully studied these bones to compare them to those of other ancient and modern humans.
00:26The remains themselves were not so unusual.
00:30We know that our human family is very diverse and that it has existed for millions of years.
00:36You know our former parent, Australopithecus, don't you?
00:40These gaiars lived in different regions of Africa and were known to walk on two legs, just like modern humans.
00:48But their brains and other parts of their body brought them closer to monkeys.
00:53It is their teeth that tell us that they were a mixture of modern monkeys and humans.
00:58Their canines were smaller than those of monkeys, but their posterior teeth were larger than ours.
01:05There were different types. Some are recognizable by their large jaws and teeth.
01:14One of the most famous fossils of Australopithecus is Lucy, an old lady of about 3.2 million years.
01:21She was discovered in Ethiopia.
01:24So we know that our family has grown a lot since then and probably even before.
01:30But it is always nice to welcome new members, which seems to be the case with this new discovery.
01:36Some of these bones look like the bones of ancient humans, while others look more like the bones of modern humans.
01:44For example, the person whose bones were discovered did not really have a chin.
01:49This means that we cannot classify her in any of the groups we know, such as the Neanderthals and perhaps even the Homo sapiens.
01:57Could it be that we are missing a branch of the human genealogical tree or an important stage of our evolution?
02:04It could be a mixture between modern human futures and those who have become what we call today the Denisovans.
02:13But it takes time to understand everything.
02:17We did not know much about the Denisovans either until we found bones in a mountain cave.
02:24These bones are very rare and we only had a few pieces to analyze.
02:28But their genes taught us a lot more about their past than their fossils.
02:33Different types of human beings have lived on this planet, but over time they have dispersed.
02:39A group went to live in Africa, it is our species, the Homo sapiens.
02:43Another group went to Europe.
02:46This is how the Neanderthals were born.
02:48But some of these ancient human groups moved to Asia.
02:52This is where we find the trace of a new interesting species, the Denisovans.
02:57It seems that these are therefore cousins of both modern men and Neanderthals.
03:02These three species actually shared a common ancestor about 765,000 years ago.
03:08We still do not know why the Neanderthals and the Denisovans followed different paths.
03:12According to a theory, this would mainly be due to the fact that the Arctic ice cap
03:17spread to the south to the Black Sea, thus separating Europe from Asia.
03:22Life, or even better, the planet, kept them at a distance for a very long time.
03:27In addition, they kept changing places of life, always looking for something better,
03:32like all other human species before and after them.
03:36But it did not last forever.
03:38Scientists have found genes from two groups of Denisovans,
03:42one in continental Asia and the other in a place called Melanesia.
03:46It seems that after thousands and thousands of years of independent development,
03:50the members of these three populations, Neanderthals, Denisovans and modern humans,
03:55were found and spread all over the Earth.
03:595% of the Denisovan genome persists,
04:02not in the region where scientists found their bones,
04:06but in people living thousands of kilometers away, in Southeast Asia,
04:10for example in Papua New Guinea.
04:13But scientists think that the cave where they found these remains of Denisovans
04:17could constitute the most northern place they have ever reached.
04:21Surviving would have been impossible for them if they had gone further north.
04:25From there, they then traveled to the south of Indonesia.
04:29This was possible for them because, at their time, the sea level was lower than today,
04:35and Indonesia was therefore connected to continental Asia.
04:39But they probably did not reach Australia, which was still separated by the ocean.
04:44And these three groups have also mixed.
04:47Scientists have found the bone of a girl whose mother was a Neanderthal and Denisovan father.
04:52It is the only first-generation hybrid human being we have discovered.
04:57She even received a nice nickname, Deni.
05:00One of the mysteries concerning the Denisovans is that of their disappearance.
05:04Perhaps they mixed so much with other humans that they merged into the mass.
05:08It is also possible that the ancestors of modern humans were stronger,
05:12that they had better tools, or that they brought diseases that did not affect them,
05:17but that affected the Denisovans.
05:20The climate and the place where they lived may also have played a role.
05:24The Denisovans lived in very diverse environments,
05:27from the cold regions of Asia to tropical Indonesia.
05:31Climate change and the challenges posed by the different habitats
05:35could have been very difficult to overcome.
05:38But it is difficult to draw strict lines in our genealogical tree.
05:43Anyway, we are only at the beginning,
05:46and who knows how many new members we are about to discover.
05:50Half a century ago, a team of scientists had the idea
05:54that a collection of fossils found in the Grand Rift Valley in Tanzania
05:58were in fact the remains of a new human species.
06:01It was at this time that we welcomed the Homo habilis into the family.
06:06It was a great discovery at the time,
06:09because people generally believed that the history of our evolution was very simple.
06:13There were first the Australopithecus, which looked like monkeys.
06:17After them, there was the Homo erectus, the standing man.
06:22He probably lived in Africa about 2 million years ago,
06:26but he quickly spread to Eurasia.
06:29It is the first human species known to have traveled such a long distance
06:32to find a better way of life.
06:35They looked like humans and behaved like them.
06:38In addition, they were probably the first of our ancestors to learn to use fire.
06:43They may also have been the first to cook food,
06:46and we are grateful for that.
06:49Food cooking is an innovation that has made the diet of humans more nutritious
06:53and that has allowed us to grow our brains and become smarter.
06:58So yes, the Homo habilis made things more complicated.
07:02They could walk on two legs, but they were also better at climbing trees
07:07than walking on the ground like us.
07:10In addition, their brains were smaller than what we expect to find in a human.
07:14At first, it seemed that these fossils came from a completely different family,
07:18linked to other creatures that looked like monkeys.
07:22But more and more extensive excavations have shown
07:25that even if these jaws and teeth were similar,
07:28the Homo habilis was bigger and a little different.
07:32Its name means « skillful man »
07:35because it was probably able to manufacture and use simple tools.
07:41The search for other fossils in Africa was not easy,
07:44because the team of researchers had to face wild animals and very challenging conditions.
07:49But they ended up finding teeth and a strange skull,
07:52which was, once again, different from the ancestors we knew.
07:58These teeth were very large,
08:00which gave rise to the new nickname of « nutcracker ».
08:04For a long time, everyone believed that this species had evolved to eat hard foods.
08:09But fossilized teeth were not very damaged,
08:12so much so that we now think that they actually ate relatively tender foods.
08:17This discovery could help us understand the evolution of our teeth.
08:22And there, in the same layers of soil where the « nutcracker » rested,
08:26the researchers found old stone tools.
08:29At first, they thought that these tools belonged to this species.
08:33But by continuing to dig,
08:35they found other fossils that did not correspond to « nutcracker ».
08:39This means that someone else had made these tools.
08:42But I will tell you this story next time.
08:46See you next time.