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The last days of the mammoths were sad and inbred

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The last days of the mammoth were bleak: the later animals were inbred, suggesting a smaller, embattled population, according to a genome analysis of two separate wooly mammoths. The two genomes, separated by tens of thousands of years, helped provide genetic clues about how the mammoth species changed over its lifetime.

The older genome represents a 45,000-year-old Siberian mammoth; the younger, a 4,300-year-old specimen found on an Arctic island, is believed to be among the last living mammoths, according to a study published today in Current Biology. But assembling the genomes meant collecting DNA samples from 10 different specimens, along with a separate tissue sample, an endeavor that required a dozen different researchers from Russia, Sweden, and the United States. The bulk of the samples came from Wrangel Island, an island off Russia's northeastern coast that's believed to have been home to the world's last mammoths.

"The parents of the younger mammoth were distant relatives."

The samples provide researchers with a rough guide to how the species developed over the course of the Pleistocene Epoch. The biggest finding is that as time went on, the mammoths' genes became less varied— suggesting a smaller and more inbred population. "We were also able to see that the parents of the younger mammoth were distant relatives, which is usually the case when populations become too small in size," says Elle Palkopoulou, a geneticist from the Swedish Museum of Natural History. That's a common pattern for declining species, but this is the best evidence yet that it happened to the last of the mammoths.

Tracking that decline required sophisticated DNA analysis. Even the most recent samples were highly degraded after thousands of years in the permafrost, so researchers compared the samples to existing genomes from African elephants. Since the African elephant genome is 99 percent similar to mammoth DNA, researchers were able to use it as a guide for assembling the damaged scraps of mammoth DNA. The result was two remarkably complete genomes. Researchers have published mammoth genomes before, starting in 2005, but this new work is more comprehensive, offering significantly more data for each position of the genome. "Only with such a high-quality, complete genome data could we investigate population size changes through time and look for signatures of inbreeding," Palkopoulou says.

The glut of genetic data has led many researchers to see mammoths as a good candidate for de-extinction — using recovered genetic data to create a mammoth embryo to be carried to term by an African elephant. It's an ambitious and controversial idea, which many researchers see as a long shot that could divert crucial resources from other conservation efforts. There are also more fundamental issues of whether the resulting creature would actually be a mammoth or just an elephant-mammoth hybrid that resembles a mammoth. It would also require significant biological and husbandry challenges beyond the collection of genetic data.

In the meantime, the research could have real implications for preserving endangered species. Genetic diversity is a constant concern for species with a small population, but this is the first study of a species that eventually went extinct. Further studies along these lines could help determine how small a population can be before it becomes genetically unsustainable, a vital issue for modern conservationists. So even if the research doesn’t end up bringing back the mammoth, it will still be a useful tool in the fight against extinction.

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