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John Henry Patterson arrived in 1898 to oversee construction of a rail bridge over Kenya’s Tsavo River. Punjabi Indians had been brought over to lay tracks, and native Taita people—agropastoralists who were suffering the effects of a drought on their corn crops and disease on their livestock—had been hired as porters. Patterson soon faced an extraordinary problem: His workers were getting eaten. In 1925, he wrote a pamphlet titled “The Man-Eating Lions of Tsavo”: “When I landed at Mombasa, I fully expected to encounter many trials and hardships while engaged in building the railway through an inhospitable and savage territory. I anticipated engineering difficulties, perils from sunstroke and fevers, a possible scarcity of food and water—but never for a moment did I realize that the African wilderness held in its mysterious recesses two prowling demons who looked upon myself and my workmen as a sort of manna sent down from Heaven for their special delectation.”
To ward them off, Patterson and his men built thick thorn bomas, burned fires, and rattled oil tins. The lions kept coming back. One night they took their supper close to Patterson’s tent. “I could plainly hear them crunching the bones,” he wrote, “and the sound of their dreadful purring filled the air and rang in my ears for days afterwards.”
Hundreds of workers eventually fled. Those who stayed behind slept on top of water tanks and in treetops, according to Patterson. During one lion attack, the workers clambered up a tree in such great numbers that it fell over. “The lions took on sort of a mythical status to the point that people thought they were invincible,” Dominy says.
After nine months of terror, Patterson finally shot and killed one of the pair. “I examined my trophy and found that it was indeed one to be proud of,” he wrote. “His length from tip of nose to tip of tail was 9 feet 8 inches; he stood 3 feet, 9 inches high, and it took eight men to carry him back to camp.” Three weeks later, Patterson killed its companion, setting off “wild rejoicings” in the camp and allowing the rail project to resume. He made the lions’ hides into trophy rugs for his flat in England. Patterson went on to fight in the Boer War and the First World War and write a 1907 bestselling book, The Man-Eaters of Tsavo. By 1924, however, he was broke and had to sell the rugs for $5,000 apiece to Chicago’s Field Museum of Natural History. Today the lions’ skins and heads are mounted over wire forms and displayed in the museum’s extensive mammals collection.
DOMINY’S INTEREST IN THE EVOLUTION of the human diet dates back to his time at Johns Hopkins, which he entered as an English major. After taking a biological anthropology class with Mark Teaford, a professor of functional anatomy and evolution at the School of Medicine, and doing fieldwork on howler monkeys in Costa Rica, he created a double major for himself. After graduating from Hopkins, earning his PhD at University of Hong Kong, and landing a postdoc at the University of Chicago, Dominy joined the faculty at Cal Santa Cruz. The university has a stable isotope laboratory, and Dominy knew that stable isotope analysis can be used to reconstruct the diets of living creatures from analyzing their teeth and bones. What might the technique reveal about the Tsavo lions?
Isotopes are atoms of the same element but with different masses because they have different numbers of neutrons. A carbon atom always has six protons in its nucleus, but carbon-12 has six neutrons, while the isotope carbon-13 has seven. These isotopes exist in various foods in different ratios, creating a sort of signature. For example, plants like corn have a higher ratio of carbon-13 to carbon-12, while legumes contain more carbon-12 than carbon-13. In a similar fashion, various plants have identifying ratios of nitrogen-14 to nitrogen-15. Critical to scientific analysis is that these ratios are passed up the food chain. When a buffalo eats grass, for example, and then a lion eats the buffalo, the isotopes from the grass become part of the lion’s tissues.
If Dominy could obtain samples of the Tsavo lions, he and his research collaborators could remove contaminating residues through a series of chemical baths, then combust the samples in a mass spectrometer. This would produce a gas that they would then propel down a tube. The tube has a sharp bend, and when the gas encountered this bend, its constituent atoms would separate by mass, with the heavier isotopes hitting the detector of the curved tube first. By measuring the impacts, the scientists could estimate the mass of each atom in the sample, which would reveal the isotope signatures.
But Dominy’s team would need samples of the Field Museum’s lions, and as Dominy says, “museum curators hate to destroy things.” During his postdoctoral fellowship at the Field, he forged relationships with museum staff that helped convince them to provide a few hairs, about 3 centimeters long, from each lion’s tail tuft. Isotope analysis of the hair samples would indicate what the lions had eaten over the last three months of their lives. “The tissues of your body are like chemical mirrors—they incorporate or reflect the chemicals in food and water that you ingest for the purpose of nourishing and maintaining your tissues,” Dominy explains. For comparative purposes, Dominy’s co-authors also obtained skin and muscle tissue from five modern Tsavo lions, as well as bone samples from 25 Tsavo herbivores, grazers and browsers that had died between 1970 and 2000.
HAIR-PROTEIN ANALYSIS OF the two man-eaters suggested they were quite different from one another in what they ate at the end of their lives. “We didn’t know what to make of it,” Dominy says. So they went back to the Field Museum and asked for bone samples. Bone grows more slowly than hair and thus reveals more about an animal’s long-term diet. In the case of the lions, which were 7 to 8 years old at the time of their deaths, bone samples would reveal their typical eating habits over their lifetimes.