Nobody knows who she was, just that she was different: a teenage girl from over 50,000 years ago of such strange uniqueness she looked to be a ‘hybrid’ ancestor to modern humans that scientists had never seen before.
Only recently, researchers have uncovered evidence she wasn’t alone. In a 2019 study analysing the complex mess of humanity’s prehistory, scientists used artificial intelligence (AI) to identify an unknown human ancestor species that modern humans encountered – and shared dalliances with – on the long trek out of Africa millennia ago.
“About 80,000 years ago, the so-called Out of Africa occurred, when part of the human population, which already consisted of modern humans, abandoned the African continent and migrated to other continents, giving rise to all the current populations”, explained evolutionary biologist Jaume Bertranpetit from the Universitat Pompeu Fabra in Spain.
As modern humans forged this path into the landmass of Eurasia, they forged some other things too – breeding with ancient and extinct hominids from other species.
Up until recently, these occasional sexual partners were thought to include Neanderthals and Denisovans, the latter of which were unknown until 2010.
But in this study, a third ex from long ago was isolated in Eurasian DNA, thanks to deep learning algorithms sifting through a complex mass of ancient and modern human genetic code.
Using a statistical technique called Bayesian inference, the researchers found evidence of what they call a “third introgression” – a ‘ghost’ archaic population that modern humans interbred with during the African exodus.
“This population is either related to the Neanderthal-Denisova clade or diverged early from the Denisova lineage,” the researchers wrote in their paper, meaning that it’s possible this third population in humanity’s sexual history was possibly a mix themselves of Neanderthals and Denisovans.
In a sense, from the vantage point of deep learning, it’s a hypothetical corroboration of sorts of the teenage girl ‘hybrid fossil’ identified in 2018; although there’s still more work to be done, and the research projects themselves aren’t directly linked.
“Our theory coincides with the hybrid specimen discovered recently in Denisova, although as yet we cannot rule out other possibilities”, one of the team, genomicist Mayukh Mondal from the University of Tartu in Estonia, said in a press statement at the time of discovery.
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