New evidence which was published in 2004 cast
doubt on the already dubious theory that sabre-toothed cats,
mammoths, and other big North American mammals were driven to
extinction by human hunting.
Genetic analysis of bison remains showed that
their populations started to crash around 37,000 years ago -
long before humans arrived in the New World, even given the
disputed maximum 30,000 year limit for their first arrival.
Researchers claimed that climate change and
other factors were far more likely culprits in the extinction.
An international team published its findings in Science magazine
in 2004 in support of this.
Until as recently as 20,000 years ago, North America
had a range of large mammals to rival the wildlife of present-day
Africa. The continent was home to woolly mammoth and mastodon, horses,
camels, giant ground sloths, and bear-sized beavers, as well as
By about 10,000 years ago, most of these animals
were gone. Some seventy North American species disappeared -
three-quarters of them large mammals. This so-called 'megafaunal
extinction' had been blamed by some on human hunters who appeared
in North America around 12,000 years ago (and quite possibly
But this latest research seriously questioned this
old hypothesis. Scientists extracted mitochondrial DNA from 442 bison
remains found in the US, including Alaska; and also in Canada, Siberia,
and China. Mitochondrial DNA, of course, comes from the cell's
'powerhouses' and is inherited through the maternal line only.
Some of the best-preserved material used in the
study was unearthed from beneath the Alaskan permafrost by gold
miners, some of whom even kept the remains refrigerated until the
scientists came to claim them. Scientists always stand a much better
chance of extracting useful DNA sequences from such frozen remains.