There's increasing evidence being teased out of human genomes that a number of ancient hominins — not just Neanderthals and Denisovans — may have contributed to the human gene pool, Discover's The Crux blog reports.
"There's a lot of evidence for some type of introgression from ancient hominins into modern humans, particularly modern humans out of Africa," Cold Spring Harbor Laboratory's Adam Siepel tells it.
The contributions of the Neanderthals and Denisovans to modern human is the most straightforward to tease out, The Crux blog notes, as samples of their DNA have been isolated from fossils. But other hominins have only left clue behind within the genomes of modern humans. New studies, it says, suggest that that the Denisovans might actually represent three different groups that contributed DNA to the ancestors of modern-day Indonesians and other, as-of-yet-unknown ancient hominins may have contributed DNA to ancestors to modern-day Africans belonging to the Mandenka, Biaka, and San tribes.
However, The Crux blog notes that without archaeological evidence it's hard to come to a certain conclusion. "The evidence for ghost lineages is building, but when scientists must rely solely on genetic evidence, it is difficult to make an airtight case for the [existence] of another species," it adds.