A mysterious "ghost population" of ancient humans lived in West Africa about 500,000 years ago, scientists believe, whose genes are thought to live on in people today.
Researchers say DNA from this group makes up between 2% and 19% of modern West Africans' genetic ancestry.
In particular they found links to the Mende people of Sierra Leone, Yoruba as well as Esan people in Nigeria, plus other groups in western areas of The Gambia.
The so-called "ghost population" of humans seems likely to have diverged from the shared ancestor of Neanderthals, Denisovans and modern humans before these lineages split about 800,000 years ago, New Scientist magazine explains.
Sriram Sankararaman - the computational biologist who led the research at the University of California in Los Angeles - told BBC Newsday he believes more such groups will be found in the future:
"As we get more data from diverse populations - and better quality data - our ability to sift through that data and excavate these ghost populations is going to get better."