Mon, Sep 26, 2016 - Page 7 News List

How we got here:
DNA points to a single
migration from Africa

Separate studies of diverse groups of humans all found that modern humans originated from one exodus from Africa

By Carl Zimmer  /  NY Times News Service

Illustration: Yusha

Modern humans evolved somewhere in Africa roughly 200,000 years ago, but how did our species go on to populate the rest of the globe?

The question, one of the biggest in studies of human evolution, has intrigued scientists for decades. In a series of extraordinary genetic analyses published on Wednesday last week, researchers believe they have found an answer.

In the journal Nature, three separate teams of geneticists surveyed DNA collected from cultures around the globe, many for the first time, and conclude that all non-Africans today trace their ancestry to a single population emerging from Africa between 50,000 and 80,000 years ago.

“I think all three studies are basically saying the same thing,” said Joshua Akey of the University of Washington, who wrote a commentary accompanying the new work. “We know there were multiple dispersals out of Africa, but we can trace our ancestry back to a single one.”

The three teams sequenced the genomes of 787 people, obtaining highly detailed scans of each. The genomes were drawn from people in hundreds of indigenous populations — Basques, African pygmies, Mayans, Bedouins, Sherpas and Cree Indians, to name just a few.

The DNA of indigenous populations is essential to understanding human history, many geneticists believe. Yet, until now scientists had sequenced entire genomes from very few people outside population centers like Europe and China.

The new data are already altering scientific understanding of what human DNA looks like, adding rich variations to our map of the genome, experts said.

Each team of researchers tackled different questions about our origins, such as how people spread across Africa and how others populated Australia. However, all aimed to settle the controversial question of human expansion from Africa.

In the 1980s, a group of paleoanthropologists and geneticists began championing a hypothesis that modern humans emerged only once from Africa, roughly 50,000 years ago. Skeletons and tools discovered at archeological sites clearly indicated that modern humans lived after that time in Europe, Asia and Australia.

Early studies of bits of DNA also supported this idea. All non-Africans are closely related to one another, and they all branch from a genetic tree rooted in Africa, the geneticists found.

Yet, there are also clues that at least some modern humans might have departed Africa well before 50,000 years ago, perhaps part of an earlier wave of migration.

For example, in Israel, researchers found a few distinctively modern human skeletons that are between 120,000 and 90,000 years old. In Saudi Arabia and India, they discovered sophisticated tools dating back as far as 100,000 years.

In October last year, Chinese scientists reported finding teeth belonging to Homo sapiens that are at least 80,000 years old and perhaps as old as 120,000 years.

Some scientists have argued from these finds that there was a human expansion from Africa earlier than 50,000 years ago.

In 2011, Eske Willerslev, a renowned geneticist at the University of Copenhagen, and his colleagues came across some puzzling clues to the expansion out of Africa by sequencing the genome of an aboriginal Australian for the first time.

Willerslev and his colleagues reconstructed the genome from a century-old lock of hair kept in a museum. The DNA held a number of peculiar variants not found in Europeans or Asians, raising knotty questions about the origins of the people who first came to Australia and when they arrived.

Comments will be moderated. Keep comments relevant to the article. Remarks containing abusive and obscene language, personal attacks of any kind or promotion will be removed and the user banned. Final decision will be at the discretion of the Taipei Times.

TOP top