Using artificial intelligence, a number of European evolutionary biologists now believe that humans have an ancient ancestor whose identity is unknown to modern science. The ancestor, based out of Asia, would have been a hybrid of Neanderthals and Denisovans, a subspecies of archaic humans.
The Denisovans are less well-known than the famous Neanderthals, but the two were separate groups who from their common ancestor around 744,000 years ago. While Neanderthals settled in Europe and parts of western Asia, Denisovan remains in central Asia and Siberia—their name comes from the Denisova Cave in the Siberian Altai Mountains, where a Denisovan bone in 2008.
The groups were genetically independent from each other. They also likely both cross-bred with modern humans. But when researching the demographics of species nearly 800,000 years ago, scientists have struggled with their complexity. That's where A.I. comes in.
Scientists trained an algorithm "to learn to predict human demographics using genomes obtained through hundreds of thousands of simulations," says Òscar Lao, principal investigator at the and an expert in this type of simulation, in a . "Whenever we run a simulation we are traveling along a possible path in the history of humankind. Of all simulations, deep learning allows us to observe what makes the ancestral puzzle fit together.”
These simulations point toward a Neanderthal–Denisovan ancestor. While it seems like a large assumption for an algorithm to make, evidence is growing in its favor. Last August, fossils were announced that showed for the first time between the two species—a female who lived 90,000 years ago with a Denisovan father and a Neanderthal mother.
Scientists generally agree that Denisovans and Neanderthals likely would have mated when the opportunity presented itself. The only problem is that there appear to be far fewer Denisovans—“the number of pure Denisovan bones that have been found I can count on one hand,” said Kelley Harris, a population geneticist at the University of Washington in Seattle who worked on the discovery of the genetic hybrid, . The Altai Mountains, the main site of any possible overlap between the populations, were likely thinly populated.
“Our theory coincides with the hybrid specimen discovered recently in Denisova, although as yet we cannot rule out other possibilities”, says Mayukh Mondal, an investigator at the University of Tartu involved with the A.I. study.
If more hybrids come forward, the algorithm's predictions would seem more plausible by the day. There's no guaranteeing its accuracy—human evolution was a messy, complicated business. But still, even the possibility of a new species is a gauntlet thrown down to archaeologists and scientists who can help further unlock the secrets of humanity's past.