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Mr. Jefferson and the Ice Age Zoo

Posted by | May 30, 2009

Thomas Jefferson had so many serious interests and accomplishments, it’s difficult to name even half of them. Besides helping to found a nation, he analyzed the gospels, started a university, promoted fine dining and bought half our continent from the French. He also squeezed in a few hours now and then to theorize about the origin of some peculiar bones dug out of the earth. (That bit of work made him a cousin to all of us geologists – or so I like to think.) But despite his brilliance in many fields, Jefferson got something important quite wrong, and we perhaps can learn from the fact that so great a mind clearly stumbled.

Up and down the eastern seaboard of North America, some odd sets of bones had been discovered in the gravel bars and riverbanks of colonial America. Many of them appeared to come from an elephant-like creature with enormous, curved tusks. No one had ever seen such an animal in the flesh. Today, every schoolchild would call the remains woolly mammoths and mastodons, but such identifications weren’t obvious if you were Joe Farmer in 1750 and you unearthed just a bone or two from a creek bank.

In 1796 Jefferson seriously studied a different set of fossil bones dug up in western Virginia. The beast was about 8-10 feet long, with a tank-like skull, thick and sturdy bones, and amazingly long claws on its paws. Jefferson first thought the animal was a great cat – a mega-lion of some sort. Later, when he read a scientific paper that came from Europe, Jefferson changed his mind and correctly identified his animal as being a type of sloth. The current scientific name of the beast, Megalonyx (great-claw) jeffersonii, honors Jefferson for his connection to the animal.

But what’s much more important to me than the old bones is that Jefferson fully expected living mammoths and great sloths to show up in the world. North America was largely unexplored, after all, and it seemed quite plausible to him that the animals might soon turn up grazing west of the Mississippi. Jefferson even asked Lewis and Clark to keep an eye out for the beasts when the famous expedition headed toward the Pacific.

To put it simply, Jefferson rejected the idea of extinction. And that remained true until his own dying day, many decades later. Extinction simply seemed to Jefferson like the wild imagining of an evil nightmare. If certain animals had dropped off the face of the whole Earth, Jefferson reasoned, others might as well. Then the whole of creation could come apart.

Like many great thinkers of his age, Jefferson could not believe that a divinely ordered Creation would include extinction. It was much easier to imagine mammoths and sloths roaming the Great Plains.

But it wasn’t long after Jefferson’s day until almost everyone accepted the idea of extinction. In part that was because exploration of the hinterlands didn’t yield living mammoths and sloths. And in part it was because more and more exotic animals – what we’d now call dinosaurs, pterosaurs, and ichthyosaurs – were being unearthed, and it was really quite clear to everyone they were not still alive (and thank goodness for that!). And there were more extinct Ice Age mammals discovered, too, ranging from saber tooth tigers a beaver as large as a modern black bear.

Two generations after Jefferson, the general public started flocking to newly built natural history museums to see the fossils of ancient monsters on display. The bigger, the scarier, the better, and school children continue that strong current of interest in the subject today in our society, with kids often more able than I am to assign the formal scientific names to dinosaurs and Ice Age mammals alike.

One of the clearest lessons of geologic history is that species are temporary – our own most likely included. We may or may not like it, but extinction is as common as dirt.

The fact that a man as brilliant as Thomas Jefferson was quite wrong about something so fundamental as extinction should make us lesser minds quite humble. But soldier on we must, with our best judgments and a reasonably tincture of self-doubt to guide us.