By Telmo PIEVANI
Humans have been migrating for a very long time, at least two million years, which is strange. Our hominid cousins ​​don’t do this. We don’t migrate like other animals, coming and going, but progressively: we just go. The common ancestor between us and chimpanzees lived in Africa between 5 and 6 million years ago. The genus Homo appeared, also in Africa, about 2.6 million years ago. By then, all the species of our subfamily, the hominins, had remained on their continent of origin. Then something happened.
WHY DID HOMO START MOVING?
The first to leave was our tall, slender ancestor, the Turkana boy, Homo ergaster. He lived in the highlands of Ethiopia, in the canyons of the Rift Valley. 2 million years ago, chasing his prey with the pace of a marathon runner, he unknowingly left Africa. With only a rudimentary spear in his hand and a huge amount of curiosity in his mind.
They spread across Eurasia, giving rise to new human species in the Caucasus, Europe, China, and the Indonesian archipelago. Why did they do this? There are two hypotheses. Perhaps they began to move to adapt to constantly changing environments. Glacial oscillations had begun, with cold periods alternating with warm periods, vegetation belts shifting, and so did springs.
In such situations, the most effective and rapid adaptation consists of following the most suitable habitat, that is, expanding like an oil slick in search of food and space. The Sahara, for example, had periods when it was green and attractive, attracting groups of sub-Saharan hominins towards the Mediterranean and the Middle East, and then it became dry again, pushing them back towards the rivers and coasts.
A second, perhaps complementary, hypothesis is that there was also a cognitive component, an exploratory curiosity: always the desire to see what was on the other side of the hill, beyond that cape on the coast, beyond the bend in the river. Unconsciously and slowly, in this way, one could start from Africa and reach all of Eurasia.
THE SECOND GREAT DIASPORA AND THE NEW SPECIES
The second great diaspora occurred 700 years ago, after a terrible glacial climate cataclysm that wiped out 98% of the human population. The planet is stronger than us and merciless. By crossing the strait, the few survivors in Africa gave birth to a new human lineage, with larger brains and more efficient technology.
Once again, they retraced the paths of the first exodus from Africa and spread throughout Eurasia, passing through the Arabian Peninsula and the Middle East. They too, through geographical separation, gave rise to new human species: Neanderthal man in western Eurasia and Denisovan man in eastern Eurasia. Migration generates species diversity. Evolution is geography, dispersal, migration, extinction. This is why the genus Homo is a bush of multiple human forms: plastic, opportunistic, mobile, flexible, nomadic. Finally, the third diaspora came: ours.
When our first direct ancestors, belonging to the species Homo sapiens, appeared in Africa, 300 years ago, the world was full of other human forms. It was a pluralistic world; there were many ways to be human. Already 130 years ago, we too began to leave Africa, and so we encountered the descendants of all the previous migrations: Neanderthals in Europe, Denisovans in Asia, two strange dwarf human species in Indonesia and the Philippines.
We coexisted with these other human species, sharing land, water, and prey. We even interbred with these other humans, producing hybrid offspring that were healthy and welcome in their communities, just as they in turn had offspring. So today, some fragments of Neanderthal and Denisovan DNA are within the genomes of populations descended from those who left Africa.
HOW THE HUMAN SPECIES SPREAD TO ALL CONTINENTS
Until 50 years ago, as many as five different human species inhabited the Earth. Then we became more invasive, they began to retreat and fade like so many flames. They lost their diversity, while we radiated into a multitude of cultures, languages, and peoples.
Eurasia in particular was a great platform for communication. It only covers a third of the planet’s land surface: 9 km without interruption, from the plains of Hungary to the Great Wall of China. Small, agile groups of hunters and gatherers of our species penetrated all the valleys of Asia, as far as the Arctic Ocean and Sulawesi, but above all, crossed the vast expanses of the Asian steppes on foot. From this perspective, Europe, geographically, is simply a closed-ended western appendage of the great Eurasian landmass.
The first African humans arrived here more than a million years ago. After they disappeared, the African ancestors of the Neanderthals arrived. Around 50 years ago, the first Homo sapiens finally arrived, with dark skin and light eyes.
Several millennia ago, the ancestors of the Aborigines reached Australia, passing through Timor and New Guinea. Long before they reached Europe, they created magnificent works of mural art.
By 45 years ago, dark-skinned sapiens hunters, having left Africa several millennia earlier, had climbed from the Altai Mountains along the Yenisei River valley, crossing Siberia and reaching the icy shores of the Kara Sea. Well-organized, they hunted large prey such as the woolly mammoth. Following the animals, they moved east, crossing an entire frozen continent now submerged, Beringia, and starting 20 years ago they invaded North America.
They spread across the vast plains, following the Pacific coast all the way to Mexico. Over the course of several millennia, they colonized Central and South America, as far as Tierra del Fuego. It was another extraordinary epic of human diversity: from that group of Siberian hunters, who adapted to every latitude from the Arctic to Patagonia, evolved thousands of Amerindian cultures, languages, and traditions. Thus, the human species expanded to every continent except Antarctica. A great story of unity in diversity. A story of migration. (Corriere della Sera)