New type of human discovered
Ker Than National Geographic News
A new type of prehistoric human has been discovered via DNA from a
child’s pinky finger found in a central Asian cave, a new study says.
“We had no inkling that this thing existed, and suddenly it’s there.
That in itself is a remarkable discovery,” a geneticist at the
University of Manchester in the UK and co-author of a news article
released alongside the study Wednesday by the journal Nature Terry Brown
said.
If confirmed by further genetic testing, the discovery dubbed X-woman
will mark the first time that a new human species has been identified
solely on the basis of DNA (quick genetics overview).
The 40,000-year-old specimen isn’t good for much else it’s far too
fragmentary to contain clues to the creature’s skeletal structure,
musculature, brainpower, or appearance, researchers say.
Out of Africa, quietly
The new-human discovery implies that there was a wave of human
migration out of Africa, the birthplace of humanity, that was completely
unknown to science.
“We think Homo erectus, an upright-walking but small-brained early
human, or hominid, was the first hominid to leave Africa two million
years ago,” Brown explained. After that the record went blank until
about 500,000 years ago, until now.
“This hominid seems to have left about a million years ago, so it
fills in a bit of a gap,” he said.
Uncanny X-woman
The fossilized pinky bone was discovered in a cave called Denisova in
the Altay Mountains of southern Siberia, Russia.
Though the pinky’s owner has been dubbed X-woman, scientists think
the pinky belonged to a child between 5 and 7 years old, but experts
can’t tell if it was a boy or a girl.
Analysis of DNA extracted from the fossil reveals it is significantly
different from the DNA of Neanderthals or of modern humans. So far only
mitochondrial DNA, or mtDNA, has been extracted. Inherited from the
mother, mtDNA contains much less information than nuclear DNA, which
contains most of a body’s genetic information.
What mtDNA lacks in storage capacity, however, it makes up in volume.
There are two copies of nuclear DNA per cell but several thousand copies
of mtDNA.
For this reason, the mtDNA of the child was much easier to read, or
sequence, explained Richard Green, an ancient-DNA expert at the Max
Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
A study of the child’s mtDNA suggests the hominid belonged to a
species that last shared a common ancestor with Neanderthals and modern
humans about a million years ago.
“We don’t know if the three species lived at the same place at the
same time,” Manchester’s Brown said. “One million years is a long time,
and populations of these hominids were not huge, so they could have been
in different parts of Europe and Asia.”
Truly a new human species
X-woman appears to be a new type of human, but is it truly a new
species?
Among the criteria used to determine whether different animals are
distinct species are inability to interbreed, genetic dissimilarity, and
anatomical variation.
It’s impossible to determine whether any of these criteria apply to
the Denisova child based solely on mtDNA.
For this reason, study co-leaders Johannes Krause and Svante Pääbo,
also of the Max Planck Institute, are planning to harvest nuclear DNA
from the fossil for analysis a painstaking process. Until then they’re
refusing to call X-woman a new species.
Green, who did not participate in the research, calls the team’s
caution “appropriate.”
Because so little bone was actually discovered, scientists have no
idea what the child looked like.
It may be possible to one day to reconstruct the Denisova child’s
features from its DNA, but that’s a long way in the future, Green said.
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