DNA study suggests hunting did not kill off mammoth

Researchers have found evidence to
suggest that climate change, rather than
humans, was the main factor that drove
the woolly mammoth to extinction.
A DNA analysis shows that the number of
creatures began to decrease much earlier than
previously thought as the world's climate
changed.
It also shows that there was a distinct
population of mammoth in Europe that died
out around 30,000 years ago.
The results have published in the Proceedings
of the Royal Society B .
The view many researchers had about woolly
mammoths is that they were a hardy,
abundant species that thrived during their time
on the planet.
But according to the scientist who led the
research, Dr Love Dalen of the Swedish
Museum of Natural History, the study shifts
that view.
"The picture that seems to be emerging is that
they were a fairly dynamic species that went
through local extinctions, expansions and
migrations. It is quite exciting that so much
was going on," he told BBC News.
Dr Dalen worked with researchers in London to
analyse DNA samples from 300 specimens
from woolly mammoths collected by
themselves and other groups in earlier studies
The scientists were able to work out how many
mammoths existed at any given time from the
samples as well as tracing their migration
patterns. They looked at the genetic diversity
in their samples - the less diverse the lower
the population
The researchers analysed samples DNA from
300 remains
They found that the species nearly went
extinct 120,000 years ago when the world
warmed up for a while. Numbers are thought
to have dropped from several million to tens
of thousands but numbers recovered as the
planet entered another ice age.
The researchers also found that the decline
that led to their eventual extinction began
20,000 years ago when the Ice Age was at its
height, rather than 14,000 years ago when the
world began to warm again as previously
thought.
They speculate that it was so cold that the
grass on which they fed became scarce. The
decline was spurred on as the Ice Age ended,
possibly because the grassland on which the
creatures thrived was replaced by forests in
the south and tundra in the north.
The reason they died out has been a matter of
considerable scientific debate. Some have
argued that humans hunted them to extinction
while others have said that changes in the
climate was the main factor.
A criticism of the climate extinction argument
is that the world warmed well before the
creatures became extinct and so that could not
have been the cause.
The new results show that mammoths did
indeed nearly go extinct between Ice Ages and
so backs the view that climate change was the
principal cause for their demise.
These results back a computer simulation of
conditions at the time carried out by
researchers at Durham University in 2010.
And of course other animals, including
humans, became more active after the Ice Age
and so competition with other species and
hunting may also have been a factor in their
extinction, though not the principle cause,
argues Prof Adrian Lister of the NHM.
"During the last ice age, between about 50,000
and 20,000 years ago, there were substantial
movements of mammoth populations -
European populations being replaced by waves
of migration from the east, for example," he
said.
"But from about 20,000 years ago onwards,
the population started the dramatic decline
that led to its extinction, first on the mainland
about 10,000 years ago, and finally on some
outlying Arctic islands. The pattern seems to fit
forcing by natural climate change: any role of
humans in the process has yet to be
demonstrated".'