How and why did our ancestors leave Africa , the cradle of humanity, to discover the world? A look back at a journey that began nearly 2 million years ago.
Before Sapiens, and after Erectus, Neanderthals were also travelers: their traces have been But the migration that most interests researchers is the third and final wave, that of its successor, Homo sapiens. Our direct ancestor appeared 200,000 years ago in East Africa – or 300,000 years ago in the Maghreb, according to recent discoveries by paleoanthropologist Jean-Jacques Hublin... For its long journey, it followed the path of its predecessor, that "obligatory corridor" which, from Ethiopia, led it to bypass the Sahara – then sometimes a green savanna, sometimes an arid desert – by following the Red Sea, then heading up the eastern coast of the Mediterranean to the Near East. It was there, in Galilee, at Qafzeh, that fossilized fragments of Homo sapiens were found in 1933. The examination of these remains – seven adult individuals and eight children – proves that their journey had begun more than 100,000 years ago. For what purpose? The hypothesis of demographic pressure that would have forced some of them to seek other resources elsewhere is not very credible. Africa was vast, the human population sparse. It is rather assumed that these humans moved slowly, at a rate of a few kilometers per generation, modifying their hunting territory based on the size of the community and animal migrations.
Did Sapiens Master Navigation?
Many of these travelers may well have moved from Africa to Eurasia without even realizing it. They reached Europe, encountered the barrier of the Alps and the cold, and settled around the Mediterranean, from Spain to Greece. And the desire to conquer mountains even took hold of them... Traces of Homo sapiens found in the interior and north of the continent indeed prove that they crossed the Alps and adapted to harsher lands. Eastern Europe and continental Asia, with their immense spaces, plains, and steppes, must certainly have seemed more welcoming to these people from the African savannas.
An adventurer, a mountain conqueror... and a navigator? Indeed, another hypothesis for the "Out of Africa" migration intrigues prehistorians: Sapiens might have used the route passing through the tip of the Red Sea, in the Bab el-Mandeb strait area, between the Horn of Africa and the Arabian Peninsula. A population mastering coastal navigation would thus have rapidly spread along the southern coast of Asia to Indonesia. The geography of this region, at a time when sea levels were lower than today, would undoubtedly have greatly facilitated human arrival. Southeast Asia was then divided into two large landmasses: the Sunda shelf, which united the Malay Peninsula, Sumatra, Java, Borneo, and about a hundred kilometers of navigation further south, the Sahul shelf, which connected New Guinea, Australia, and Tasmania. One certainty: it was by sea, 60,000 years ago, that Homo sapiens arrived in Australia, as evidenced by a skeleton found on the shores of Lake Mungo. Geological studies have also proven the disappearance, 50,000 years ago (10,000 years after human arrival), of large species of marsupial mammals and birds. Undoubtedly a consequence of the presence of Homo sapiens, the first "modern" humans.
The first stage is complete. The second will take place later, 30,000 years ago, when humans set out to "conquer" America, then connected to Siberia, in the far east of Asia. It is thought that they may have arrived by sea aboard vessels made of tree trunks, following the coasts of Siberia and Alaska during milder periods when the current Bering Strait was submerged. Excavations conducted in the Santa Elina rock shelter in Mato Grosso, Brazil, push human presence on the American continent back to 25,000 years ago. They still had a few territories left to explore, and not the least: 13,000 years ago, having further perfected their techniques to face the harshest environments, modern humans reached the Arctic Ocean and, shortly after, at the other end of the earth, touched the extreme tip of South America. Much later – only 1,000 years ago – the most remote Pacific islands would be colonized. The conquest of the Earth was then complete...
Several Species Coexisted with Sapiens
What can we learn from this long journey of modern humans? First, that Sapiens was not alone and encountered many "cousins" during its travels. While it belongs to a lineage of hominids that appeared in Africa 10 million years ago, it did not flourish as the result of a linear and continuous evolution. It is rather the sole survivor of a "bush of species," as Jean-Jacques Hublin writes (Quand d’autres hommes peuplaient la Terre, Flammarion, 2008). Like the paranthropuses, early Homo representatives, still close to australopithecines, they disappeared without descendants 1 million years ago, even as other Homo species coexisted and prospered for a long time. Without the chance occurrences and necessities that pushed one branch to develop into Sapiens, the Earth could very well have remained populated by chimpanzees or hosted a completely different form of humanity... This is how, 28,000 years ago, Neanderthals, the cousin and ultimate competitor of Sapiens in Eurasia, disappeared. Not that the latter's superiority was overwhelming, since the two species coexisted for centuries, "as long as the time elapsed since the construction of the pyramids to the present day," specifies Jean-Jacques Hublin. A sudden cooling of the climate, scarcity of habitable territories, Neanderthal's cultural and physical inferiority, a demographic decline that brought this population below its renewal threshold... The causes of its extinction remain mysterious, as does the dominance of Sapiens. How did the latter supplant hominid species to "control the planet"? The question fascinates the public, which has given a triumph to Sapiens, A Brief History of Humankind (ed. Albin Michel, 2015), the phenomenon book by Israeli historian Yuval Noah Harari.
From an evolutionary perspective, we therefore belong to a very young species. And considering that a territory as large as present-day France was populated by only about fifteen thousand individuals for millennia, one realizes that human history is truly a miracle!
Only Sapiens Reached America and Australia
Prehistory is subject to controversy and, of course, touches upon the question of origins. Homo sapiens, of which we are a part, migrated across the entire planet. But did they leave Africa following the tracks of their ancestors, Homo erectus, or did they appear in all corners of the world? For seventy years, two theses have been in conflict. The first, known as "Out of Africa" (or monocentric), presumes that we all originate from a single hearth and that Sapiens left East Africa 100,000 years ago. Everywhere, it would have replaced older human species, including Homo erectus, who would have left Africa before them. The second, known as "multiregional," estimates that Homo sapiens is an evolution of Homo erectus. It therefore appears in all regions colonized hundreds of thousands of years earlier by its "ancestor," and would have continued its journey. Where Erectus would have stopped in Central Asia, Sapiens would have conquered Australia and North and South America... The debate remains open.