DNA Reveals “Genetic Meltdown” Decimated the Last Woolly Mammoths

Woolly mammoth. Photo by Flying Puffin.
Woolly mammoth. Image: Flying Puffin.

Woolly mammoths are the most famous of all Ice Age fauna, and they roamed the frozen wastelands of North America and Eurasia until they died out roughly 10,000 years ago.

Their extinction is generally blamed on climate change and hunting by humans; but as mammoth populations shrank, other factors contributed to their demise.

On Wrangel Island, a remote island northeast of Russia in the Arctic Ocean, woolly mammoths were isolated from humans and thrived in frigid, favorable climate. However, despite these ideal conditions, they completely died out 4,000 years ago. Why?

When any animal population shrinks, the genetic pool shrinks as well. This results in inbreeding and “genetic meltdown”, which can obliterate an entire species. If just a handful of the population becomes diseased, the species does not have enough genetic variation to successfully survive, and all members will die. Similarly, if just a handful of the population develops a harmful genetic mutation, the mutation will eventually pollute the population, and all members will die.

Woolly mammoth and musk ox remains on Wrangel Island. Photo by Ansgar Walk.
Woolly mammoth and musk ox remains on Wrangel Island. Image: Ansgar Walk.

In recent years, scientists have been mapping the woolly mammoth genome in an attempt to better understand and resurrect this legendary species. Now, they have finally completed the mammoth DNA sequence in at least two different mammoths. The first mammoth came from the mainland population 45,000 years ago when mammoths were at their peak. The second mammoth came from the Wrangel Island population 4,300 years ago when mammoths finally went extinct.

The mainland mammoth possessed healthy DNA free of negative genetic mutations, since it was part of a large, healthy population. However, the isolated Wrangel Island mammoth possessed DNA fraught with loss-of-function mutations. The mammoth had lost its sense of smell; it had lost urinary proteins used to attract a mate; and it had developed silky, satin-colored fur.

Obviously, these mutations negatively affected the Wrangel Island population, and they create a window into the cause of their extinction. However, they also demonstrate how contemporary species on the brink of extinction can fall victim to “genetic meltdown” as well.

With small, fragmented populations of gorillas, rhinos, elephants, tigers, pandas, and other critically endangered species, these animals are all at the mercy of genetics. They are playing an involuntary game of Russian roulette, and disease and loss-of-function mutations are the bullet.

This is why conservation is important, even for species with large populations and healthy genes. When an endangered species experiences a negative genetic mutation, and it becomes rampant in the population, we currently have relatively little control over the species’ survival.

Check out the controversial mission to resurrect the mammoth: