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By diving into some of the oldest African DNA on record, scientists have found a number of missing chapters to the story of humans, including a mysterious “ghost” lineage of humans whose identities remain unknown.
The groundbreaking study carried out an in-depth analysis of ancient DNA from western Africa for the first time. Reported in the journal Nature this week, an international team of researchers sequenced DNA from four children buried in two phases 8,000 and 3,000 years ago in Shum Laka, a cave site in the Grasslands region of Cameroon.
Africa is the sole setting for chapter one of the human story. Not only did our whole species emerge from this massive continent, but it also holds more human genetic diversity than any other part of the planet to this day. Through comparing this ancient genetic material to DNA from a range of present-day African people, the team was able to gain some incredible insights into the early journey of Homo sapiens across Africa.
"Our analysis indicates the existence of at least four major deep human lineages that contributed to people living today, and which diverged from each other between about 250,000 and 200,000 years ago," David Reich, senior author of the study from Harvard Medical School, said in a statement.
These four human lineages include present-day central African hunter-gatherers, southern African hunter-gatherers, all other modern humans, and – most intriguing – an unknown “ghost” population of modern humans. While the identity of this “ghost” lineage remains a mystery, the ancient individuals found at Shum Laka harbored about two-thirds of their ancestry from them, while the rest of their ancestry stemmed from a lineage related to present-day central African hunter-gatherers.
The analysis also highlighted another set of later lineages that split off around 80,000 to 60,000 years ago, including the lineage leading to all present-day non-Africans. Another surprise to emerge from the analysis was the relationship between the ancient people and modern-day speakers of Bantu, the most widespread and diverse group of languages in Africa today.
It's thought that Bantu originated in this area of Central Africa, before spreading across the lower half of Africa. However, unexpectedly, the analysis suggests that present-day Bantu-speakers living in Cameroon and across Africa do not descend from the population to which the Shum Laka children belonged.
It looks like the origins of Bantu, along with the wider migrations of ancient humans, remain a lot more fiddly than often presumed.
"These results highlight how the human landscape in Africa just a few thousand years ago was profoundly different from what it is today, and emphasize the power of ancient DNA to lift the veil over the human past that has been cast by recent population movements," continued Reich.
