DNA From Child Burials Shows ‘Exceptionally Different’ Human Landscape in Ancient Africa

Children’s skeletons give genomes more than 3000 years old

Central Africa is far too hot and humid for ancient DNA to survive– or so scientists assumed. Currently, the bones of four children buried thousands of years earlier in a rock shelter in the grasslands of Cameroon have given enough DNA for scientists to examine.

It is the first ancient DNA from human beings in the region, and as the team reports today in Nature, it holds several surprises. For one, the region today is the homeland of Bantu speakers, the majority group in western and Central Africa. The children ended up being most closely related to hunter-gatherers such as the Baka and Aka– groups typically referred as “pygmies”– who today live at the very least 500 kilometers away in the rainforests of western Central Africa.

“In the presumed cradle of Bantu languages and, for that reason, Bantu people, these individuals are basically ‘pygmy’ hunter-gatherers,” claims Lluís Quintana-Murci, a population geneticist at the Pasteur Institute and CNRS, the French national research agency, who was not involved the brand-new study. He and others had long presumed that these groups had a wider variety before the Bantu population exploded 3000 years earlier.

The second huge surprise came when the team compared the children’s DNA to various other genetic data from Africa and discovered hints that the Baka, Aka, and other Central African hunter-gatherers come from one of the most ancient lineages of modern human beings, with origins going back 250,000 years.

Genetic lineage of Central Africa

In the new research study, geneticists and archaeologists took samples from the DNA-rich inner ear bones of the four children that were buried 3000 and 8000 years earlier at the well-known archaeological site of Shum Laka.

The scientists managed to sequence high-grade complete genomes from two of the children and partial genomes from the additional two. Comparing the sequences to living Africans, they found that the four children were distant cousins. All had acquired roughly one-third of their DNA from ancestors most closely related to the hunter-gatherers of western Central Africa. The other two-thirds of children’s DNA originated from an ancient “basal” source in West Africa, including some from a “long lost ghost population of contemporary humans that we did not know about in the past,” states population geneticist David Reich of Harvard University, leader of the study.

The discovery highlights the diversity of African groups that lived in the continent prior to the Bantus starting to herd livestock in the grassy highlands of western Central Africa. The Bantus made ceramics and forged iron, and their growing populations rapidly displaced hunter-gatherers across Africa. Examining DNA from a time before this expansion gives “a peek of a human landscape that is exceptionally different from today,” Reich says.

The team compared the children’s DNA to ancient DNA extracted previously from a 4500-year-old individual from Mota Cave in Ethiopia and sequences from other ancient and living Africans, utilizing various statistical methods to figure out just how they all were related, which groups came first, and when they divided from one another.

A new model

The team’s bold brand-new model pushes Central African hunter-gatherer beginnings to 200,000 to 250,000 years earlier– not long after our species evolved. The model suggests their lineage split from 3 other modern-day human lineages: one resulting in the Khoisan hunter-gatherers in southern Africa, one to eastern Africans, and one to a now-extinct “ghost” population.

Early diversification of modern humans fits the huge variation seen in fossils of early Homo sapiens, claims paleoanthropologist Katerina Harvati of the University of Tübingen, which is not part of this study. The lineages would certainly have parted company and moved into different parts of Africa 200,000 to 250,000 years ago, preserving their distinctions by only occasionally interbreeding at the borders.

However, others state that although the new research study offers compelling new evidence, the data are not yet strong enough to build a trustworthy model. “It requires to be further tested with additional entire genome data from both contemporary and, preferably, ancient DNA from more Africans,” claims evolutionary geneticist Sarah Tishkoff of the University of Pennsylvania.

That might be possible. A third essential lesson from the study is that ancient DNA can be harvested from bones in Central Africa, after all. “The future is not as grim for ancient DNA in these regions,” claims population geneticist Joshua Akey of Princeton University.

Read the original article on Science.

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