Wednesday, January 29, 2020

The mysterious DNA of unknown people discovered in Cameroon

The DNA of four prehistoric children, discovered in western Cameroon, highlights the genetic traces of extinct human populations. This mysterious “ghost” line could rewrite the history of human evolution.

Diving into the oldest African DNA ever collected, scientists have discovered a mysterious “ghost” line of humans whose identity is still unknown. It was at the archaeological site of Shum Laka, in Cameroon, that scientists made this extraordinary discovery. It was reported in the scientific journal Nature. 

Cradle of Homo sapiens 

For the first time, an international team of researchers from Harvard Medical School in Boston, USA, has sequenced the DNA of four children, who were buried in two phases 8,000 and 3,000 years ago, to Shum Laka. This iconic archaeological site is located in caves in the Prairies region of Cameroon, near Bamenda. It is known to be the cradle of the history of our species, Homo sapiens. It also has the particularity of harboring the greatest human genetic diversity in the world. 

"The ancient DNA found there is the first to be discovered in west-central Africa and one of the oldest ever recovered from a tropical African environment", confirms a press release published on the website from the University of Montreal. 

"Our analysis indicates the existence of at least four great deep human lines which contributed to the life of people of today, and which diverged from each other approximately 250,000 to 200,000 years ago", David Reich, the lead author of the Harvard Medical School study, insists in the same press release.

The Shum Laka site in Cameroon could reveal new secrets about the history of human evolution. 

These four human lines include the current hunter-gatherers of Central Africa, the hunter-gatherers of southern Africa, all other modern humans and - even more intriguing - a "ghost" population, hitherto unknown, of other humans. modern. Although the identity of this last line remains a mystery, the old individuals having already been discovered in Shum Laka are for two thirds of them from them, while the rest of their ancestry comes from a line linked to hunters -current collectors from Central Africa. 

Extremely rare 

"Shum Laka is a point of reference for understanding the secular history of central-west Africa," says Isabelle Ribot on the University of Montreal website. This anthropologist searched the graves of 18 people (mostly children) buried in two phases between 8,000 and 3,000 years ago. Human skeletons from before the Iron Age are extremely rare here. Tropical environments and acidic soils are not conducive to bone preservation. This is why the results of the study are truly "exceptional". 

Harvard Medical School scientists sampled the petrous bones (inner ear) of six individuals buried in Shum Laka. Four of these samples produced ancient DNA and were directly dated at the Pennsylvania State University Radiocarbon Laboratory. Molecular conservation has made it possible to analyze the entire genome of ancient DNA.

A past marked by population movements 

And the researchers found that none of the individuals sampled at Shum Laka were closely related to most of the current speakers of Bantu, the most widespread group of African languages. Rather, they were part of a distinct population that lived in the region over five millennia ago and which was then replaced by very different groups whose descendants make up the majority of Cameroonians today. 

"These results underscore how profoundly different the human landscape in Africa was just a few thousand years ago from what it is today," said David Reich. They highlight the power of ancient DNA to lift the veil on a human past that has been masked by recent population movements. "