Scientists discovered evidence pointing to a previously unknown ancestor of humans after cutting the human genome using artificial intelligence.
According to a paper published in nature Communications by a team of researchers in Spain and Estonia, human ancestors existed about 80,000 years ago. The new evidence can help explain the genetic links between modern humans and our ancestral cousins, Denisovans and Neanderthals.
An abundance of evidence suggests that early Homo sapiens interfered with Neanderthals, which left Africa more than 200,000 years earlier than Homo sapiens did. Denisovans was only added to human relative in 2008 after the discovery of a pinkie leg and a tooth in a Siberian cave, but genetic analysis has shown that interbreeding also occurred between Homo sapiens and Denisovans.
But the study's author notes, Homo sapien's breeding with these two other hominid species alone could not account for all the inexplicable genetic residues present in the modern human genome. A third human ancestor's interbreeding with ancient people seemed credible, but until quite recently there was no evidence to support the existence of a third ancestor in the mix.
In last summer, a research group found a bone fragment in Russia that belonged to a child who was perceived by a Neanderthal mother and Denisovan's father. This remarkable finding suggested that not only Homo sapien's interbreeding with Neanderthals and Denisovans, but these two species were also interbreeding with each other.
Read more: A hybrid of humanity's closest relatives has been identified in 50,000-year-old bones
This discovery appeared to point to the hypothetical missing third species that could account for the unexplained parts of the modern human genome. The impeded genetics that were introduced were to map not only Neanderthal and Denisovan interbreeding, but also interbreeding between Homo sapiens and a Neanderthal-Denisovan hybrid.
According to a statement from the Barcelona Center for Genomic Regulation, one of the three institutions involved in the research was "Mapping these demographics" "much more complex than what is hitherto considered" to analyze human development.
The usual statistical tools used by geneticists would simply not cut it, and so the researchers went into deep learning.
Deep learning is a type of machine learning that uses a network architecture loosely modeled on the human brain to analyze massive amounts of information for complex patterns. The workers backward with deep learning fed the researchers the network of various demographic models of ancient populations that included this Neanderthal-Denisovan hybrid until it created a genome that matched the modern human genome.
This suggests that the missing ancestors of humans may well be the by-product of Neanderthal-Denisovan interbreeding.
"When we run a simulation, we travel along a possible path in the history of humanity," says Oscar Lao, a population geneticist at the Center for Genomic Regulation and a leader in the study, in a statement. "With all simulations, deep learning allows us to observe what makes the ancestral brush fit together."
Researchers still need more evidence to finally join our ancient history. Mayukh Mondal, an evolutionary biologist at the University of Tartu and a co-author of the study, admitted in a statement that "we cannot yet exclude other opportunities".