Hints
of an unidentified, extinct human species have been found in the DNA of modern
Melanesians – those living in a region of the South Pacific, northeast of
Australia.
According
to new genetic modelling, the species is unlikely to be Neanderthal or
Denisovan – two ancient species that are represented in the fossil record – but
could represent a third, unknown human relative that has so far eluded
archaeologists.
“We’re
missing a population, or we’re misunderstanding something about the
relationships,” Ryan Bohlender, a statistical geneticist from the University of
Texas, told Tina Hesman Saey at Science News.
Bohlender
and his team have been investigating the percentages of extinct hominid DNA
that modern humans still carry today, and say they’ve found discrepancies in
previous analyses that suggest our mingling with Neanderthals and Denisovans
isn’t the whole story.
It’s
thought that between 100,000 and 60,000 years ago, our early ancestors migrated
out of Africa, and first made contact with other hominid species living on the
Eurasian landmass.
This
contact left a mark on our species that can still be found today, with
Europeans and Asians carrying distinct genetic variants of Neanderthal DNA in
their own genomes.
And that’s not all they’ve given us.
Earlier
this year, researchers investigated certain genetic variants that people of
European descent inherited from Neanderthals, and found that they’re associated
with several health problems, including a slightly increased risk of
depression, heart attack, and a number of skin disorders.
And
a separate study published earlier this month found evidence that modern
genital warts – otherwise known as the human papillomavirus (HPV) – were
sexually transmitted to Homo sapiens after our ancestors slept with
Neanderthals and Denisovans once they left Africa.
While
our relationship with Neanderthals has been widely researched, how we
interacted with the Denisovans – the distant cousins of Neanderthals – is less
clear.
The
problem is that Neanderthals are well represented in the fossil record, with
many remains having been uncovered across Europe and Asia, but all we have of
the Denisovans is a lone finger bone and a couple of teeth that were found in a
Siberian cave in 2008.
Using
a new computer model to figure out the amount of Neanderthal and Denisovan DNA
carried by modern humans, Bohlender and his colleague found that Europeans and
Chinese people carry a similar amount of Neanderthal DNA: about 2.8 percent.
That
result is pretty similar to previous studies have estimated that Europeans and
Asians carry, on average, between 1.5 and 4 percent Neanderthal DNA.
But
when they got to Denisovan DNA, things were a bit more complicated,
particularly when it came to modern populations living in Melanesia – a region
of the South Pacific that includes Vanuatu, the Solomon Islands, Fiji, Papua
New Guinea, New Caledonia, West Papua, and the Maluku Islands.
As
Hesman Saey explains for Science News:
“ Europeans have no hint of
Denisovan ancestry, and people in China have a tiny amount – 0.1 percent,
according to Bohlender’s calculations. But 2.74 percent of the DNA in people in
Papua New Guinea comes from Neanderthals. ”
“ And Bohlender estimates
the amount of Denisovan DNA in Melanesians is about 1.11 percent, not the 3 to
6 percent estimated by other researchers ”
“ While investigating the
Denisovan discrepancy, Bohlender and colleagues came to the conclusion that a
third group of hominids may have bred with the ancestors of Melanesians. ”
“Human history is a lot more complicated than we thought it
was,”
he told her.
This
find is supported by a separate study by researchers from the Natural History
Museum of Denmark, who analysed DNA from 83 Aboriginal Australians and 25
locals from the Papua New Guinea highlands.
As
we reported last month, this was the most comprehensive genetic study of
Indigenous Australians to date, and it indicated that they are the oldest continuous
civilization on Earth, dating back more than 50,000 years ago.
But
the results revealed something else – DNA that was very similar to that of the
Denisovans, but distinct enough for the researchers to suggest that it could
have come from a third, unidentified hominid.
“Who
this group is we don’t know,” lead researcher Eske Willerslev told Hesman Saey.
Until
we have more concrete evidence of this hypothesized third human species (some
fossils would be nice), we can’t prove this, and we should point out that
Bohlender’s estimates have yet to be formally peer-reviewed, so they might
shift with further scrutiny.
And
it could be that our identification of Denisovan DNA is more ambiguous than we
think, given that our only source is a finger bone and a couple of teeth.
But
the evidence is mounting that our interactions with ancient humans were far
more complex than we’d assumed, which shouldn’t be much of a surprise, when you
think about it.
Just
because we don’t see them in the fossil record doesn’t mean they didn’t exist –
preserving the remains of something for tens of thousands of years isn’t easy,
and then someone has to be in the right place at the right time to dig them up.
Hopefully,
the more we investigate the genetic make-up of our most ancient societies, the
more hints we’ll get of the rich and complicated history our species shared
with those that didn’t make it to modern times.
So
much incredible findings of an unknown DNA surface, we may need to think twice
before saying that we are ‘alone’ in the universe.
The results of Bohlender’s analysis were presented last week
at the 2016 American Society of Human Genetics meeting in Canada.
Source
: simplecapacity.com