Nobody knows
who she was, just that she was different: a teenage girl from over 50,000 yearsago of such strange uniqueness she looked to be a 'hybrid' ancestor to modern
humans that scientists had never seen before.
Only now,
researchers have uncovered evidence she wasn't alone. In a new study analysing
the complex mess of humanity's prehistory, scientists have 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", explains 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 now a
third ex from long ago has been 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 write 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 last year; although it's
early days, 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", says one of the team, genomicist Mayukh Mondal from the University of Tartu in Estonia.
That being
said, the discoveries being made in this area of science are coming thick and
fast.
Last year
another team of researchers identified evidence of what they called a
"definite third interbreeding event" alongside Denisovans and
Neanderthals, and a pair of papers published just a fortnight ago traced the
timeline of how those extinct species intersected and interbred in clearer
detail than ever before.
There's a
lot more research to be done here yet. Applying this kind of AI analysis is a
decidedly new technique in the field of human ancestry, and the known fossil
evidence we're dealing with is amazingly scant.
But
according to the research, what the team has found explains not only a
long-forgotten process of introgression – it's a dalliance that, in its own
way, informs part of who we are today.
"We
thought we'd try to find these places of high divergence in the genome, see
which are Neanderthal and which are Denisovan, and then see whether these
explain the whole picture," Bertranpetit told Smithsonian.
"As it
happens, if you subtract the Neanderthal and Denisovan parts, there is still
something in the genome that is highly divergent."
The findings
are reported in Nature Communications.
Comments
Post a Comment