The original humans of West Africa are partly descendant from a human species that is now extinct and of which we had no knowledge of, up until now. A new investigation carried out by scientists from the University of California in Los Angeles (USA), has reached this conclusion after the genetic analysis of four current African populations.
We have no fossils but genetic evidence that an ancient, human-like population left a genetic legacy in today's West Africans. These extinct relatives of Homo sapiens passed on genes to the African ancestors of the modern Yoruba and Mende approximately 24,000 years ago or more, according to experts in the study published by Science Advances. The DNA suggests that the genetic differences are so important that the source had to be a completely different hominid. These are a species of archaic hominids which, unlike Neanderthals and Denisovans, modern science has never found physical remains.
The genomes of the Yoruba and Mende groups contain a considerable percentage of the genetic material of this mysterious "ghost population. The unexplained DNA found in people living in West Africa today does not match Neanderthals or Denisovans.
The researchers analyzed the genomes of more than 400 people from four West African populations of the 1000 Genome Project, including the Yoruba and Mende populations.
Using a computer modelling technique, they found that between 2 and 19% of their genetic ancestry was derived from an unaccounted-for source. Who was this?
This is where genetic introgression comes in, in other words, the gene flow that takes place when members of two populations mate and the resulting hybrid individuals reproduce with members of the parental populations. It is perfectly feasible that the hominid in question could be an entirely new species of early humans, whose ancestors would have split off from the human family tree before the ancestors of the Neanderthals and the Denisovans.
Some of the DNA segments passed down from this new Homo species have been found to influence survival-enhancing functions, including tumour suppression and hormone regulation. Experts suspect that these genes spread rapidly among modern West Africans.
Background on other studies
Interestingly, this is not the first time that 'ghost' species of extinct ancestors unknown in modern DNA have been found, but it is the first time that it has been observed in modern West African DNA. The findings are supported by several studies which suggest that there have been multiple crossover events between archaic and modern human populations in Africa.
The authors say we will need more analysis of African genomes across the continent before we can understand the true composition of our ancestors. The journey through our history continues.
Reference: Recovering signals of ghost archaic introgression in African populations. Arun Durvasula1 and Sriram Sankararaman. Science Advances 12 Feb 2020: Vol. 6, no. 7, eaax5097 DOI: 10.1126/sciadv.aax5097