A third extinct “ghost species” beyond Neanderthals and Denisovans that interbred with anatomically modern humans has been unveiled by researchers from Spain and Estonia using artificial intelligence. This third extinct species is likely a hybrid or close relative of Neanderthals and Denisovans that crossbred with “Out of Africa” modern humans in Asia.
The existence of a third ghost population follows the discovery in August 2018, of a bone fragment from a girl whose mother was a Neanderthal and father was a Denisovan in a remote cave in Siberia. In the study, researchers estimate that this hybrid child lived between 79,100 and 118,100 years ago. Modern humans, scientists discovered, share a common ancestor with Denisovans and Neanderthals that lived roughly 600,000 years ago. Later — approximately 390,00 years ago — the Neanderthal and Denisovan lineages split.
Both Neanderthals and Denisovans are distinct species in the genus Homo that coexisted and interbred with modern humans over 40,000 years ago, reports Kristen Hovet for the Genetic Literacy Project: “While some experts contend that Neanderthals and Denisovans fall under the same category as Homo sapiens, since together they satisfy one definition of “species” — a group of organisms whose members have the ability to produce fertile, viable offspring — the general consensus is that they are separate species.”
The third archaic species was revealed using “a demographic model based on deep learning in an Approximate Bayesian Computation framework,” the researchers wrote in their article published in Nature Communications last month. “We have an overwhelming support for the existence of a third extinct branch of the Neanderthal-Denisovan clade,” the researchers said.
We know that bout 80,000 years ago, a group of anatomically modern humans left the African continent and migrated to other areas of the world, crossbreeding with Neanderthals in all the continents, except Africa, and with the Denisovans in Oceania and probably in South-East Asia,” said Jaume Bertranpetit, principal investigator at the Institute of Evolutionary Biology.
Anatomically modern humans evolved in Africa between 200,000 and 300,000 years ago, then migrated to the rest of the world starting around 50,000 to 80,000 years ago. Recent fossil evidence suggests that Homo sapiens left in several waves of migration, as opposed to a sole migratory event. Our genomes carry the marks of their ancient interactions, including inherited genetic risks and benefits.
Tibetans, for example, writes Hovet, have Denisovan gene variants associated with hemoglobin concentration and an adaptive response to hypoxia (lack of oxygen) that adapted them to life high in the Himalayas. “Tibetans utilize five gene variants that collectively make them well adapted to the low oxygen levels, extreme cold, elevated levels of ultraviolet light and limited food supplies that characterize high-altitude living,” according to Andrew Masterson for Cosmos Magazine.
Another example reports Hovet, is celiac disease, a hereditary illness affecting more than one in 100 people and has been linked to known celiac alleles inherited from Neanderthal ancestors: “While celiac disease presents many everyday hurdles for those diagnosed, and is associated with increased chance of death in celiacs who go undiagnosed or misdiagnosed, celiac alleles are also associated with survival advantages. These advantages include increased protection against bacterial infections and dental decay.”
The Daily Galaxy, Andy Johnson, via Genetics Literacy Project
Image credit top of page: Human Ghost Species YouTube