Mammoth Hair Yields Ancient DNA, Study Says
for National Geographic News
|September 27, 2007|
The thick coats of shaggy hair that kept woolly mammoths warm on the icy tundra have yielded enough intact DNA to sequence their genomes, a new study reports.
In addition to helping scientists figure out why mammoths went extinct, the feat could pave the way for better and faster genetic studies of other ancient animals.
Scientists obtained ten complete mitochondrial genomes using tufts of hair from mammoths that died between 50,000 and 12,000 years ago in what is now northern Siberia, a region of Russia.
Mitochondrial DNA is passed from mother to offspring, so it helps scientists sort out lineages, determine genetic diversity, and address other population mysteries (get a genetics overview).
Before this study, only seven mitochondrial genomes from extinct animals had been created: four from ancient birds, two from mammoths, and one from the mammoth's elephant-like relative the mastodon.
The DNA used to create such genomes usually comes from bone or muscle, which degrade quickly and are easily contaminated with genetic material from other sources such as bacteria.
The process of finding enough uncontaminated DNA to piece together a complete genome from bone or muscle can take several years.
"It is not very efficient," said Stephan Schuster, a study co-author and associate professor of biochemistry and molecular biology at Pennsylvania State University.
"On the other hand, the hair shaft is like a biological plastic, and the bacteria cannot penetrate it."
Schuster and a team of international colleagues report their findings in tomorrow's issue of the journal Science.
Schuster's team devised a method to retrieve unharmed DNA from below the mammoth's hair shaft.
The researchers first wash the hair to rid the outside of any contaminants and then dissolve the strands in a solution.
"We get high-precision, high-fidelity ancient DNA sequences," Schuster said.
The DNA was then used to sequence the mitochondrial genomes.
Schuster and colleagues are now analyzing the woolly mammoth genomes to help figure out exactly what caused the mammoths' extinction at the end of the last ice age about 10,000 years ago.
The comparisons will show when genetic diversity declined—a sign of population weakness.
This date can then be correlated with other events that might have led to the mammoths' downfall, such as climate warming, the arrival of humans, or outbreaks of disease.
What's more, Schuster noted, his team found that the same technique of retrieving ancient DNA from hair works well with hair samples from other animals that coexisted with mammoths.
"If you would find that the genetic diversity collapsed not only for one species [the mammoth] but also for several species, then this will help you to understand what the entire ecosystem looks like," he said.
In addition, the technique could be used to retrieve a complete nuclear genome of an extinct animal, Schuster said.
"This is basically what we're doing right now," he said.
Such full genetic data may open the door to bringing a mammoth back to life.
Michael Hofreiter is an evolutionary geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who led the team that retrieved the first woolly mammoth genome from bone.
He said the new technique reported in Science is an excellent advance, particularly for robust population genetic analyses—as long as hair is available.
"For mammoths it's great, but for most extinct animals we don't have hair samples," he said.
For example, his group is now working on ancient DNA from cave bears, which lived in Europe and also went extinct about 10,000 years ago.
(Related news: "Ancient Bear DNA Mapped—A 1st for Extinct Species" [June 6, 2005].)
Hundreds of thousands of cave bear bones are available for study, he said, "but there's not a single hair preserved."
Schuster and colleagues, however, are undeterred.
They note that one of the mammoth genomes they sequenced is from the famous Adams mammoth, which was pulled from the permafrost in 1806 and has been kept in a museum at room temperature ever since.
"[This] puts a large number of collections stored in natural history museums within reach of molecular genomic analysis," the team writes in the paper, "and may also allow us to add molecular-genetic data to the collections of Charles Darwin, Alexander von Humboldt, and Carl von Linné [also called Linnaeus]."
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