Mammoth DNA explains extinction
2008-11-20 11:09
Washington - Researchers have sequenced the gene map of a long-extinct, mummified woolly mammoth, using DNA taken from its hair.
The sequence shows that mammoths were more closely related
to modern, living elephants than previously thought, and they
found some elements, such as evidence of inbreeding, that may
shed light on why the giant creatures went extinct, the
researchers reported on Wednesday.
And it shows that it is possible to reconstruct the genomes
of extinct creatures, they reported in the journal Nature.
"By deciphering this genome we could, in theory, generate
data that one day may help other researchers to bring the
woolly mammoth back to life by inserting the uniquely mammoth
DNA sequences into the genome of the modern-day elephant,"
Stephan Schuster of Pennsylvania State University, who helped
lead the research, said in a statement.
"This would allow scientists to retrieve the genetic
information that was believed to have been lost when the
mammoth died out, as well as to bring back an extinct species
that modern humans have missed meeting by only a few thousand
years."
Evolved slowly
The sequence shows that mammoths, which died out around
10 000 years ago, evolved slowly.
"We discovered that individual woolly mammoths were so
genetically similar to one another that they may have been
especially susceptible to being wiped out by a disease, by a
change in the climate, or by humans," said Schuster.
The researchers will have to analyze the DNA to pinpoint
some of the precise sequences unique to mammoths, but have some
hints.
"Our data suggest that mammoths and modern-day elephants
separated around six million years ago, about the same time
that humans and chimpanzees separated," added Penn State
biologist Webb Miller, who directed the study.
But mammoths and elephants appear more closely related than
humans and chimpanzees are. Miller said the findings can help
scientists understand evolution.
The researchers have been pulling DNA out of mummified
mammoths and their hair for more than a decade, but because it
is so old, the DNA is broken down. It is also contaminated by
bacteria and fungi.
Mammoths offer a better target than most extinct animals
because many of their bodies have been frozen since death -
some so thoroughly that the meat is still edible.
The Penn State researchers believe they have about 80% of its genome complete.
Two groups
The evidence suggests that woolly mammoths then separated
into two groups around 2 million years ago, which eventually
became genetically distinct. One went extinct 45 000 years ago,
while another survived until 10 000 years ago.
Next in line - perhaps Neanderthals, said Michael
Hofreiter of the Max Planck Institute for Evolutionary
Anthropology in Leipzig, Germany.
"The next draft nuclear genome of an extinct species likely
to become available is that of our closest relative, the
Neanderthal, following on from publication of a complete
Neanderthal mitochondrial genome sequence," Hofreiter wrote in
a commentary.
A fast sequencing machine made by 454 Life Sciences, a
Roche company, made the work possible, the researchers said. So
far, 28 mammals have had their genomes sequenced, including
humans, dogs, cats, rats and pigs.