| WASHINGTON, July 2
WASHINGTON, July 2 How do Tibetans thrive in
high-altitude, low-oxygen conditions that would make others
wither? Well, they may have received some help from an
Scientists said on Wednesday many Tibetans possess a rare
variant of a gene involved in carrying oxygen in the blood that
they likely inherited from an enigmatic group of extinct humans
who interbred with our species tens of thousands of years ago.
It enables Tibetans to function well in low oxygen levels at
elevations upwards of 15,000 feet (4,500 meters) like the vast
high plateau of southwestern China. People without this variant
would be apt to develop thick blood, leading to high blood
pressure, heart attacks, strokes, low-birth-weight babies and
higher infant mortality.
This version of the EPAS1 gene is nearly identical to one
found in Denisovans, a lineage related to Neanderthals - but is
very different from other people today.
Denisovans are known from a single finger bone and two teeth
found in a Siberian cave. DNA testing on the 41,000-year-old
bone indicated Denisovans were distinct from our species and
"Our finding may suggest that the exchange of genes through
mating with extinct species may be more important in human
evolution than previously thought," said Rasmus Nielsen, a
computational biology professor at the University of California,
Berkeley and the University of Copenhagen, whose study appears
in the journal Nature.
Our genome contains residual genetic fragments from other
organisms like viruses as well as species like Neanderthals with
which early modern humans interbred. The researchers called
their study the first to show that a gene from an archaic human
species has helped modern humans adjust to different living
"Such exchange of genes with other species may in fact have
helped humans adapt to new environments encountered as they
spread out of Africa and into the rest of the world," said
Asan Ciren, a researcher with China's BGI genomics center,
added, "The genetic relationship or blood relationship between
modern humans and archaic hominins is a hot topic of the current
The researchers said early modern humans trekking out of
Africa interbred with Denisovans in Eurasia en route to China.
Their descendants harbor a tiny percentage of Denisovan DNA.
Genetic studies show nearly 90 percent of Tibetans have the
high-altitude gene variant, along with a small percentage of Han
Chinese, who share a common ancestor with Tibetans. It is seen
in no other people.
The researchers conducted genetic studies on 40 Tibetans and
40 Han Chinese and performed a statistical analysis showing that
the gene variant almost certainly was inherited from the
The gene regulates production of hemoglobin, a protein in
red blood cells that carries oxygen. It is turned on when blood
oxygen levels drop, stimulating more hemoglobin production.
At elevations above 13,000 feet (4,000 meters), the common
form of the gene boosts hemoglobin and red blood cell
production, causing dangerous side effects. The Tibetans'
variant increases hemoglobin and red blood cell levels only
modestly, sparing them these effects.
(Reporting by Will Dunham; Editing by Grant McCool)