Scientists discovered evidence pointing to an ancestor previously unknown to humans after tracking the human genome using artificial intelligence.
According to an article published in Communications of nature For a team of researchers in Spain and Estonia, the human ancestor existed about 80,000 years ago. This new evidence could help explain the genetic links between modern humans and our ancestral cousins, the Denisovans and the Neanderthals.
A lot of evidence suggests that the first Homo sapiens crossed with the Neandertals, which left Africa more than 200,000 years before Homo sapiens. Denisovans were only added to the human lineage in 2008 after the discovery of a pinky bone and tooth in a Siberian cave, but genetic analysis has shown that the cross between Homo sapiens and Denisovans also occurred.
But, the authors of the study point out that Homo sapiens that reproduces with these other two hominid species alone could not explain all the unexplained genetic remains found in the modern human genome. A third human ancestor that crossed with ancient humans seemed plausible, but until recently there was no evidence to support the existence of a third ancestor in the mix.
Last summer, a team of researchers found a fragment of bone in Russia that belonged to a child conceived by a Neanderthal mother and a father Denisovan. This remarkable finding suggested that not only were Homo sapiens crossed with Neanderthals and Denisovans, but these two species also crossed each other.
Read more: A hybrid family of those closest to humanity has been identified in a bone of 50,000 years
This discovery seemed to point to the third hypothetical missing species that could explain the unexplained parts of the modern human genome. The obstacle that the geneticists faced was to map not only the Neanderthal and Denisovan crossover, but also the interbreeding between Homo sapiens and a Neanderthal-Denisovan hybrid.
According to a statement from the Genomic Regulation Center of Barcelona, one of the three institutions involved in the research, the mapping of these demographic data was "much more complex than anything else considered to date" with regard to the analysis of human evolution
The usual statistical tools used by geneticists simply would not cut it, so the researchers began to learn in depth
Deep learning is a type of machine learning that uses a network architecture freely modeled in the human brain to analyze large amounts of information for complex patterns. Working back with deep learning, the researchers fed the network several demographic models of ancient populations that included this Neanderthal-Denisovan hybrid until it produced a genome that matched the modern human genome.
This indicated that the lost ancestor of humans could be the by-product of the Neanderthal-Denisovan crossover.
"Every time we run a simulation, we are going down a possible path in the history of humanity," Oscar Lao, a population geneticist at the Center for Genomic Regulation and co-leader of the study, said in a statement. "Of all the simulations, deep learning allows us to observe what makes ancestral puzzles fit."
However, researchers still need more evidence to conclusively reconstruct our ancient history. Mayukh Mondal, an evolutionary biologist at the University of Tartu and co-author of the study, acknowledged in a statement that "so far we can not rule out other possibilities."