Why don't we have woolly mammoths any more?
Anyone who has watched the animated Ice Age films, or the disaster movie "The Day after Tomorrow" will know that the woolly mammoth, seen above in an artist's impression of mammoths moving through melting snow, disappeared around the time of the end of the last ice age. A mammoth has not walked the Earth for the last 10 000 years. village at mammoth mountain
New research published in PLoS Biology, the open access journal, reveals why mammoths disappeared when they did. This adds to research information about th woolly mammoth that has all come to light over the last few years.
Woolly mammoth DNA tests
Although the last woolly mammoth died 10 000 years ago, some of the remains of the species remain buried in the permafrost, where they have been well preserved for thousands, sometimes tens of thousands of years.
Three sets of scientific study over the last five years have looked at the possibiity of getting DNA from some of this preserved tissue to sequence the DNA of the woolly mammoth. This ancient DNA analysis has been remarkably successful, showing that this type of DNA genetics is a fast moving scientific field.
Two research groups have been able to extract DNA from frozen mammoth bones. One set of scientists looked at the mitochondrial DNA from a woolly mammoth that lived 12 000 years ago and showed that its closest living relative is most likely to be the Asian elephant (not the African elephant).
The material that the other group analysed was from a woolly mammoth that had lived even longer in the past - 28 000 years ago. They looked at the mitochondrial DNA and also some of the nuclear DNA, which was in quite good condition.
No mammoth specimen is too old to give us its DNA for testing...
It is quite unusual for studies of animals that died this long ago to look at the DNA from the nucleus of the animal's cells. Ancient DNA extraction is a tricky business. Ancient DNA studies usually look only at the DNA from inside the mitochondria, but these stretches of DNA can be very small and need a lot of amplication in order to study them. This mass copying of the sequences can introduce errors.
In one of the latest studies, as reported in PLoS Biology, the scientists Evgeny Rogaev, Yuri Moliaka, and their Russian colleagues sequenced the complete mitochondrial genome of a woolly mammoth that died 33 000 years ago..This represents the oldest sequenced mitochondrial genome and—at 16,842 base pairs—the longest stretch of sequenced DNA from an extinct Pleistocene species. This analysis, like the Nature study, points to the Asian elephant as the mammoth's closest relative.
Woolly mammoths fell behind in genetic diversity...
Another finding of the study was that the genetic diversity among the mammoths of the time was relatively low - which may be another factor in why they became extinct. A population with low genetic diversity is not able to cope with environmental changes as effectively as a population with a high genetic diversity. So, the woolly mammoth may not have reacted quickly enough the the changes in its world, speaking in evolutionary terms. | 
