What killed the Neanderthals?
- The Sixth Extinction: An Unnatural History by Elizabeth Kolbert
Bloomsbury, 336 pp, £12.99, February 2014, ISBN 978 1 4088 5122 7
In 1739, Captain Charles Le Moyne was marching four hundred French and Indian troops down the Ohio River when he came across a sulphurous marsh where, as Elizabeth Kolbert puts it, ‘hundreds – perhaps thousands – of huge bones poked out of the muck, like spars of a ruined ship.’ The captain and his soldiers had no idea what sort of creatures the bones had supported, whether any of their living kin were nearby and, if so, what sort of threat they presented. The bones were similar to an elephant’s, but no one had seen anything like an elephant near the Ohio River, or indeed anywhere in the New World. Perhaps the animals had wandered off to the uncharted wilds out west? No one could say. The captain packed up a massive circular tusk, a three-foot-long femur and some ten-pound teeth, carried them around for several months as he went about the tricky task of eradicating the Chickasaw nation, and finally delivered the relics, after a stopover in New Orleans, to Paris, where they confounded naturalists for several decades.
A contemporary reader may guess, correctly, that the bones belonged to a species of animal that had long since ceased to exist – in fact, they came from the Mammut americanum, the American mastodon – but at the time such an imaginative leap would have been very difficult, because it hadn’t yet occurred to anyone that an entire species could cease to exist. ‘Aristotle wrote a ten-book History of Animals without ever considering the possibility that animals actually had a history,’ Kolbert writes, and in Linnaeus’s Systema Naturae, published four years before Le Moyne’s discovery, ‘there is really only one kind of animal – those that exist.’ The French naturalist Georges-Louis Leclerc thought the bones might belong to a species that, uniquely in history and for reasons unknown, had disappeared from the Earth, but his conjecture was widely rejected. Thomas Jefferson put forward the consensus view in 1781, in his Notes on the State of Virginia: ‘Such is the economy of nature, that no instance can be produced of her having permitted any one race of her animals to become extinct; of her having formed any link in her great work so weak as to be broken.’
In 1796, Georges Cuvier presented a new theory: nature did permit links to be broken, sometimes a lot of them all at once. Cuvier, just 27, was teaching at the Paris Museum of Natural History, one of the few institutions to survive the Terror, and had spent many hours studying its collection of fossils and bones. He noticed that the teeth of Le Moyne’s incognitum had unusual little bumps on them, like nipples. He was convinced they couldn’t be elephant teeth. He called their owner mastodonte, ‘breast tooth’. Other remains were similarly unmatched to the contemporary world: the elephant-sized ground sloth, called megatherium, bones of which had been discovered near Buenos Aires and reassembled in Madrid (Cuvier worked from sketches); the meat-eating aquatic lizard (now called mosasaurus), whose massive fossilised jaw had been picked out of a quarry near Maastricht; the woolly mammoth, whose frozen remains were everywhere in Siberia. Such creatures must have populated a lost world. ‘But what was this primitive earth?’ Cuvier asked. ‘And what revolution was able to wipe it out?’
These were interesting questions, but Cuvier’s contemporaries were slow to consider answers. More and more they were coming to accept that occasionally species might disappear – Darwin would soon propose that ‘the appearance of new forms and the disappearance of old forms’ were procedurally ‘bound together’ by natural selection – but evolution was a gradual process. Mass extinction, ‘revolution’, was something else. The claim that nature could undergo a sudden radical shift seemed not just historically unfounded but scientifically (and perhaps politically) untenable. Charles Lyell countered Cuvier’s anarchic ‘catastrophism’ with stately ‘uniformitarianism’. All change, geological or biological, took place gradually, steadily. Any talk of catastrophe, Lyell admonished, was ‘unphilosophical’.