How Species Go Extinct: The Case Of The Woolly Mammoth

When humans first arrived in the Americas at least 13,000 years ago, they found a continent filled with huge animals (megafauna, as the scientists call them).  They included giant ground sloths, anteaters, saber-toothed tigers, and of course the woolly mammoth.

These elephant-like animals had never seen humans before and probably didn’t have much fear of them, given their relatively tiny size.  But as we know, no species on Earth can be quite as deadly as a group of human hunters with weapons.  The result was a constant barbecue, as humans dined on the mammoth bonanza and began to thrive and multiply on the new continent.

I always wondered how these humans could have knowingly killed the last few mammoths, with the species in what should have been an obvious decline.  But as it turns out, they may not have had to wipe them out completely to put the mammoth into a death spiral.

A new UC Berkeley study indicates that inbreeding from a smaller population may have done the trick:

To test the theory that woolly mammoths’ genomes changed as their population declined, researchers compared existing genomes from a mainland mammoth that dates back to 45,000 years ago, when the animal was plentiful, to one that lived about 4,300 years ago. The recent genome came from a mammoth that had lived in a group of about 300 animals on Wrangel Island in the Arctic Ocean.

“We found an excess of what looked like bad mutations in the mammoth from Wrangel Island,” Rogers said.

The analysis showed that the island mammoth had accumulated multiple harmful mutations in its genome, which interfered with gene functions. The animals had lost many olfactory receptors, which detect odors, as well as urinary proteins, which can impact social status and mate choice. The genome also revealed that the island mammoth had specific mutations that likely created an unusual translucent satin coat.

To be sure, some people believe that the Ice Age was the real culprit in killing off the mammoth.  But mammoths had survived multiple ice ages in the past and emerged okay.  I’m sure the stress of human hunters, combined with the Ice Age, was a deadly twofer.  But the impact of hungry people with spears and the resulting inbreeding could very well have been enough to send the species into extinction.

Unfortunately, it’s not dissimilar to our current condition of a growing, hungry, meat-eating population and a rapidly changing climate.