Genes indicate Europeans descended from very few Africans
EDINBURGH, Scotland (AP) Modern Europeans, and maybe populations in other parts of the world, are descended from no more than a few hundred Africans who left their homeland as recently as 25,000 years ago, new research suggests.
The findings, reported at the start of a conference of the Human Genome Organization, the international collaboration researching the genetic makeup of the human race, provide the first estimate of how many people founded Europe.
They are also a blow to a rival theory that modern humans evolved in parallel in Africa, Europe and Asia from multiple populations of early humans.
"I think this certainly rules that out, at least in respect to Europe," said study leader Eric Lander, director of the Whitehead Institute/Massachusetts Institute of Technology Center for Genome Research. "We're not sure whether this was just the founding of Europe or whether, in fact, this small bottleneck represents all the people leaving Africa."
Lander's study involved comparing about 300 chromosomes from people in Sweden, Central Europe and Nigeria. The differences in the genetic pattern between the European and African chromosomes revealed how long ago Europeans left Africa and about how many there must have been.
The pattern showed that the Europeans were descended from fewer ancestors than the Africans - an evolutionary bottleneck, Lander said.
"It's hundreds, not thousands," Lander said.
The Nigerian chromosomes had been well-shuffled around, which indicates a wide gene pool and a long breeding history, while the European chromosomes had long stretches of unshuffled genetic material, indicating a much smaller number of chromosome types entering the mix.
"I think he's right," said Eddy Rubin, head of the human genome center at the Lawrence Berkeley National Laboratory at the University of California, Berkeley. "The evidence is overwhelming that present-day Europeans come from a very small group that stayed small for a while, then expanded."
Rubin was not involved with Lander's study.
"We are going to be able to do this throughout much of the rest of the world. The data will be able to rule it in or out for the other populations very quickly," Lander said.
"We're still in the early days for this, but it is remarkable how much the human chromosomes can be read as a history book," he continued. "We are going to be able to say how populations are related to each other, when people arrived there and how many people likely arrived in different places."
The human race numbers about 6 billion people, but it largely has the genetic variation of a population of a few tens of thousands, Lander said.
"We really are a tiny species grown large in the blink of an eye," he said.