Mammoths moved 'out of America'
By Elizabeth MITCHELL
Scientists have discovered that the last Siberian woolly mammoths may
have originated in North America. Their research in the journal Current
Biology represents the largest study of ancient woolly mammoth DNA. The
scientists also question the direct role of climate change in the
eventual demise of these large beasts. They believe that woolly mammoths
survived through the period when the ice sheets were at their maximum,
while other Ice Age mammals "crashed out".
The iconic Ice Age woolly mammoth - Mammuthus primigenius - roamed
through mainland Eurasia and North America until about 10,000 years ago.
Previous studies had hinted that the last mammoths left in Siberia were
not natives - but immigrants from North America. However, more evidence
was required to strengthen the case for this "out of America" theory.
A team of researchers led by Professor Hendrik Poinar from McMaster
University in Canada collected 160 mammoth samples from across
Holarctica - a region encompassing present day North America, Europe and
Asia. Well-preserved DNA material - between 4,000 and 40,000 years old -
was obtained from "almost every part of the animal - even from preserved
hind, skin and hair", Professor Poinar told BBC News.
They analysed DNA from mitochondria - genetic material which is
passed from mother to offspring via the egg - and can be used to track
the ancestry of a species back many hundreds of generations. The genetic
information confirmed that a North American mammoth population
overturned those endemic to Asia.
Mammoth migration
It is hard to speculate why the North American woolly mammoths
returned to Siberia. "Presumably, conditions were favourable on the
Bering land bridge which was more of a large filter than an open
highway," suggested Professor Poinar. The expansion of North American
forests may have "pushed the mammoths along", he added.
At the same time, the native Siberian mammoths, which may have been
around for much of the Middle Pleistocene, completely disappeared. It is
unclear if the Siberian mammoths experienced a "natural decline" or if
they were out competed by the North American immigrants.
The endemic Siberian population had different molar features and a
"very unique DNA signature" - that was dated to be almost 900,000 years
old. It is possible that it may not have been a true woolly mammoth -
but a more primitive species.
"Many people thought that this (primitive) species had become extinct
way before 38,000 years ago," said Professor Poinar. "Palaeontologists
were not so happy because these are the intricacies of DNA that are very
difficult to discern based on mammoth tusks and teeth," he added.
Scientists are now beginning to understand the dynamic evolutionary
history of these Ice Age mammals. "This study adds to a growing body of
evidence about just how dramatic and tumultuous the Pleistocene climate
actually was," Dr Beth Shapiro, a scientist from Penn State University
in the US, told BBC News.
"With ancient DNA, we can actually go back in time and look directly
at these old populations. "Here we have evidence of local extinctions,
replacements and long-distance dispersals," she explained. |