In 1898, in what served as the inspiration for the movie The Ghost and the Darkness, a pair of lions in Kenya killed and devoured about 135 railway workers building the Kenya-Uganda Railway before being shot by project leader Lieutenant-Colonel John Henry Patterson. Now known as the man-eating lions of Tsavo, the reason why the animals developed a taste for human flesh has been a mystery, but microscopic analysis of their remains by a Vanderbilt University team puts the blame on bad teeth.

The construction of the railway linking Uganda with the Indian Ocean would be of little interest outside of railway buff circles if it hadn't been for the frightening events of March through December of 1898. During that time, the British were building a bridge for the line over the Tsavo River, but two male lions started to stalk the Indian workmen, attacking them and dragging them off to be eaten. Despite attempts to frighten the lions off, trap them, or build defenses against them, the death toll mounted until Patterson managed to hunt down and shoot the killers.

The remains of the lions eventually ended up the the Chicago Field Museum of Natural History, where they are on display, but why these animals started to attack humans instead of their normal prey was never determined. Until now, the favored theory was that a severe drought and a rinderpest epidemic had so deprived the lions of food that they were reduced to scavenging and then attacking the railway camp. However, modern science has provided another explanation.

"It's hard to fathom the motivations of animals that lived over a hundred years ago, but scientific specimens allow us to do just that," says Bruce Patterson, MacArthur Curator of Mammals. "Since The Field Museum preserves these lions' remains, we can study them using techniques that would have been unimaginable a hundred years ago."

Larisa DeSantis, assistant professor of earth and environmental studies at Vanderbilt University, took the skulls of the Tsavo lions, plus a third man eater from Mfuwe, Zambia that ate six people in 1991, and used state-of-the-art dental microwear analysis to examine the wear patterns on their teeth.

What they found was that the lions didn't show any evidence that they had been consuming normal prey in the time before their death, nor were they scavenging. If they had, their teeth would have shown the distinct pattern caused by gnawing and breaking bones. Instead, the wear patterns resembled those of zoo lions, which usually eat soft foods like beef and horsemeat.

3D models of the microscopic wear patterns of lion teeth  – two on the top left are from wild-caught lions, top right is from a captive lion, the two bottom left are from the Tsavo man-eaters(Credit: The Field Museum of Natural History)

In addition, Patterson and DeSantis say that previous chemical analysis of the Tsavo lions' remains indicates that they suffered from severe dental disease and one had a root-tip abscess in one of its canines. Anyone who's had toothache or a case of gum infection and can't handle a tough steak can sympathize with the animals, who would have found it impossible to catch and kill zebras and buffalos by running them down and suffocating them with their teeth clamped about their prey's windpipe.

The team say that the lions probably switched to attacking humans because they were easier to catch and more tender to eat. This is partly supported by the fact that the Tsavo lion with less dental injuries still supplemented its anthropophagous diet with zebras and buffalos. In addition, the Mfume lion showed dental problems, as have written accounts of man-eating lions and leopards in colonial India.

"Our data suggests that these man-eating lions didn't completely consume the carcasses of their human or animal prey," says DeSantis. "Instead, people appear to have supplemented their already diverse diet. Anthropological evidence suggests that humans have been a regular item on the menu of not only lions, but also leopards and the other great cats. Today, lions seldom hunt people, but as human populations continue to grow and the numbers of prey species decline, man eating may increasingly become a viable option for many lions."

The results were published in Nature: Scientific Reports.

The video below discusses the Tsavo Man Eaters.

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