The last woolly mammoths on earth were inbred but not doomed to extinction, says a new study.
The Last of the Mammoths
During the climax of the Ice Age, woolly mammoths once roamed across Europe, Asia, and the northern reaches of North America. As the global climate started warming some 12,000 years ago, these animals retreated northwards.
The human hunters must also have become a mounting threat. Thus, the woolly mammoths became extinct in this continent some 10,000 years ago.
The last woolly mammoth breathed its final breath on an island off the coast of present-day Siberia 4,000 years ago. What exactly sealed their fate has remained unknown until now.
A number of theories have risen resembling this unhappy event. One of them holds the view that harmful genetic mutations by inbreeding cause a "genetic meltdown" within an isolated population.
Mammoths are a fine system for knowing current views from the genetic viewpoint concerning the exact process that occurs when a species experiences a population bottleneck. That is because they embody the fate of so many present-day populations, according to Marianne Dehasque of Uppsala University.
Unraveling the Mystery of Extinction
New genetic analysis suggests that such a freak event, such as an extreme storm or plague, might likely be blamed as the cause. The result is discussed in the paper "Temporal dynamics of woolly mammoth genome erosion prior to extinction."
Genome Assembly of the Woolly Mammoths: A team of researchers led by Love Dalén, researcher and evolutionary geneticist, analyzed genomes from 13 mammoth specimens tainted with bones found on Wrangel Island in Russia. To compare, it also analyzed seven earlier excavated specimens from the mainland. Together, the specimens represent a 50,000-year time span.
These facts lead to the conclusion that the Wrangel population has undergone an extremely strong bottleneck once it has been reduced to an effective size of eight individuals. Within 20 generations, the group recovered to a population that was stable until very recently at 200-300.
Probably one of the clearest signals in Wrangel Island mammoth genomes, compared to their ancestors from the continent, were hallmarks of inbreeding and low genetic diversity that extended into genes known to play an important role in the vertebrate immune response. A herd like this should have been less robust to novel pathogens, such as a plague or avian influenza.
The findings bring into question the theory of genetic meltdown. This latest research confirms that while this group had low genetic diversity, it remained a stable population of a few hundred mammoths occupying the island for thousands of years before suddenly going extinct.
Thus, as a team, one can confidently rule out the notion that the woolly mammoth population was just too small and that they were doomed to go extinct for genetic reasons. It means, explains Dalén, some random events just killed them off-and we would still have mammoths today if only that random event hadn't happened.
According to Dr. Vincent Lynch, a biologist at the University at Buffalo, the findings give new insights into the finals days of mammoths and open up the possibility that a genetically compromised group would be able to respond to an environmental change, like a pathogen.
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