Where was the Garden of Eden? DNA has the answer

Modern humans originated from a so-called “Garden of Eden” situated to the south of the Zambezi River in Botswana, scientists have discovered.

In a major new study of DNA, understood to be the first of its kind, researchers “traced back the maternal genetic lineage of anatomically modern humans (Homo sapiens sapiens)” and found it “most closely resembles people living in a small area of southern Africa”, The Telegraph reports.

For decades, scientists had thought that modern humans had developed all over Africa. “This [study] enabled us to pinpoint the ancestral homeland of all humans. It is the first time the exact location has been identified,” the authors said.

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So what did the researchers find and are they definitely right?

What does the study say?

Sky News reports that the study Human origins in a southern African palaeo-wetland and first migrations, published in the journal Nature this week, says that “for 70,000 years, our ancestors thrived in the area before changes in climate turned what was Africa’s largest lake into what is now the Kalahari Desert”.

This change, according to the researchers, forced the population to migrate elsewhere between 130,000 and 110,000 years ago, “sparking the development of their genetic, ethnic and cultural diversity”.

The researchers have posited that the shift in the region’s climate may have been caused by an alteration in the orbital tilt of the Earth, allowing the inhabitants to move north.

Geological evidence suggests the homeland region once housed Africa’s largest ever lake system, known as Lake Makgadikgadi.

And climate computer model simulations indicate that “the slow wobble of Earth’s axis” brought “periodic shifts in rainfall” across the region.

What do the findings mean?

Study co-author Professor Axel Timmermann, a climate scientist at Pusan National University in South Korea, said: “These shifts in climate would have opened green, vegetated corridors, first 130,000 years ago to the north east, and then around 110,000 years ago to the south west, allowing our earliest ancestors to migrate away from the homeland for the first time.”

Fellow author Professor Vanessa Hayes, a geneticist at the Garvan Institute of Medical Research in Australia, said: “It has been clear for some time that anatomically modern humans appeared in Africa roughly 200,000 years ago”, but it had not previously been figured out where in Africa they had originated.

“What has been long debated is the exact location of this emergence and subsequent dispersal of our earliest ancestors,” she added. “It’s an extremely large area, it would have been very wet, very lush, it would have provided a suitable habitat for modern humans and wildlife to have lived.”

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What have other experts said?

But not everyone is convinced by the study’s findings. Professor Chris Stringer, of London’s Natural History Museum, told the Daily Mail that he doubted whether mankind’s first “base” could be determined by one aspect of DNA alone. The study had focused primarily on something known as L0 mitochondrial DNA, which people inherit from their mother.

“I’m cautious about using modern genetic distributions to infer exactly where ancestral populations were living 200,000 years ago, particularly in a continent as large and complex as Africa,” he said. “And, like so many other studies that concentrate on one small bit of the genome, or one region, or one stone tool industry, or one ‘critical’ fossil, it cannot capture the full complexity of our origins.”

Instead of L0, Stringer suggested that focusing on the Y-chromosome could yield clearer results.

“When we look at the male-inherited Y chromosome, the most divergent lineages currently known in extant humans are found in West Africa, not South Africa,” he said, adding that previous research suggests we are in fact an “amalgam of ancestry from different regions of Africa”, as scientists had previously believed.