Two maneless male lions stand in a glass case at the Field Museum in Chicago. In March 1898 they began dragging railway workers out of their tents along the Tsavo River in Kenya, where several thousand laborers were camped to build a single bridge for the British. Thorn fences and all-night fires did nothing. Hundreds of workers fled, construction stopped, and the Prime Minister, Lord Salisbury, had to explain the delay to the House of Lords. Lieutenant Colonel John Henry Patterson spent months hunting the pair and finally killed them in December.

Patterson claimed the lions had killed 135 people, and for a century his book was the accepted account. Then science examined the remains. Isotope analysis in 2009 showed the two had eaten the equivalent of about 35 people, though many more were probably killed and not consumed. DNA work in 2024 went further still. The picture that emerges is of two bonded brothers pushed toward human prey by a cattle plague, an old slave route, and a bad tooth.

• The first lion measured nine feet eight inches and took eight men to carry. The second absorbed nine shots from three rifles over several days.
• Patterson used the skins as floor rugs for 25 years before selling them to the Field Museum in 1924 for $5,000.
• Hair packed into the lions’ teeth yielded DNA from zebra, oryx, waterbuck, wildebeest, giraffe, and humans, and proved the two were brothers who groomed each other.
• A rinderpest outbreak had wiped out much of their natural prey, and the river crossing had long been scattered with the dead of slave caravans.
• The lion that ate about 24 people had a broken canine and a root abscess. Tooth wear shows the injury came well before Patterson’s rifle, despite his claim.