Out of Africa
Between 50,000 and 80,000 years ago a single group of around 150-200 Homo sapiens crossed the horn of Africa into Arabia. From there they went on to colonize the world. This small tribe is the forebear of us all. What drove this first migration and what does that tell us about our evolution?
In 1967 a team led by Richard Leakey found two hominid skulls and some bones near the Omo River in Ethiopia. And 38 years later dating techniques established that they were 195,000 years old. So we now know that Homo sapiens, or anatomically modern man, evolved in Africa at least 195,000 years ago.
In 2016 studies were published by three separate teams of geneticists who collected and examined DNA from 787 people from hundreds of indigenous populations around the globe. They revealed that all non-Africans today trace their ancestry to a single population, emerging from Africa between 80,000 and 50,000 years ago.
Our species tried multiple times to leave Africa as climatic changes made it necessary and possible. People in Papua New Guinea carry a trace of DNA from an earlier wave of Africans who left the continent as long as 140,000 years ago, and then disappeared. One group of H. sapiens, discovered in Israel, left Africa across the area we now know as the Sahara desert at a time when it was fertile. They died out when drought returned to the region, leaving skeletal remains that are between 120,000 and 90,000 years old. Sophisticated tools that date back as far as 100,000 years ago have been found in Saudi Arabia and India; and Chinese scientists have found teeth belonging to H. sapiens that appear to be as old as 120,000 years.
Our successful human journey out of Africa began approximately 30,000 years later, by which time we had spread to other parts of Africa as far south as the Cape of Good Hope. Between 60,000 and 40,000 years ago, Africa was depopulated by drought, and our own ancestral population shrank to only about 5,000 members. By taking advantage of falling sea levels, a small group of about 150-200 of them managed to cross into Arabia via the Red Sea. Scientists estimate that lower sea levels would have meant that the gap between the continents was only about 8 miles, which they somehow managed to cross.
It seems that from the very start, human beings have moved on in search of better living conditions: food, space and relative safety. As new births swelled their numbers, a group would divide and so prevent the discord that emerges in large foraging populations. One group would remain and the other would move on to unclaimed territory. Geneticists’ maps show that we travelled from Arabia to India to Japan and Australia.
40,000 years ago we were sharing the planet with Neanderthals, Denisovans, Homo floresiensis and possibly the last remnants of Homo erectus. As the psychologist Thomas Suddendorf points out in his book The Gap, it’s only because all the other hominids went extinct along with, until quite recently, all evidence of their existence that we began to think of ourselves as vastly different and superior from other primates.
Thanks to DNA studies, we know that the common ancestor of all non-Africans interbred with Neanderthals at least four times and that the Melanesian peoples also interbred with Denisovans. The complete story continues to unfold: genomes of present-day Aboriginal Australians, for example, are thought to perhaps include traces of an ancient liaison with an unknown hominid group.
“What you can see from the DNA of all non Africans is that they all belong to one tiny African branch that came across the Red Sea. … If it was easy to get out of Africa we would have seen multiple African lineages in the DNA of non-Africans but that there was only one successful exit suggests it must have been very tough to get out. It was much drier and colder then.” says Dr. Stephen Oppenheimer, a geneticist at the school of anthropology at Oxford University, who has also led research on the genetic origins of humans outside Africa.
The Bradshaw Foundation, in association with Dr. Stephen Oppenheimer invite you to
take a virtual journey out of Africa with modern man, travelling over the last 160,000 years.
The map shows the interaction of migration and climate over this period.