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Two male lions became infamous for terrorizing and eating humans in 1898 during construction of a railway bridge over the Tsavo River in Kenya. Now, an innovative genetic analysis of hairs trapped inside the cavities of their broken teeth have revealed new insights into the prey the so-called Tsavo man-eaters once hunted.
The harrowing true story of the lions, which raided tents in the camp at night and dragged victims into the thicket, has inspired movies and books over the years — and copious research to understand what drove them to prey on humans.
The lions killed at least 28 people, including those working on the Kenya-Uganda Railway, beginning in April 1898 before civil engineer Lt. Col. John Henry Patterson shot the massive cats. Patterson then sold the lions’ remains in 1925 to Chicago’s Field Museum of Natural History, where they have since remained.
Thomas Gnoske, a collections manager at the museum, first spotted thousands of hairs trapped within the lions’ teeth when he examined their skulls in the 1990s.
Now, Gnoske and his colleagues in Kenya, at the Field Museum and the University of Illinois Urbana-Champaign have been able to isolate single hairs and clumps of hairs compacted within the tooth cavities and extract DNA from them to identify the animals to which they belonged. The lion duo ranged farther than previously believed in their hunt for food, the findings suggested.
The research published Friday in the journal Current Biology. The team also said the method could reveal links between living predators and their prey as well as in specimens dating back hundreds of thousands of years ago.
“A key part of this study was to create a method to extract and analyze DNA from single hairs of prey species found in the teeth of historical museum specimens,” said lead study author Alida de Flamingh, postdoctoral research fellow at the University of Illinois Urbana-Champaign, in a statement. “Our analysis showed that the historic Tsavo lions preyed on giraffe, human, oryx, waterbuck, wildebeest, and zebra, and we also identified hairs that originated from lions. This method can be used in many ways, and we hope other researchers will apply it to study prey DNA from other animal skulls and teeth.”
Getting up close with the man-eaters
Gnoske and his colleague and study coauthor Julian Kerbis Peterhans, an adjunct curator at the Field Museum and professor of natural science at Roosevelt University, have studied the lion skulls for decades.
Gnoske made the discovery that both lions were adult males, although both lacked the signature manes associated with fully grown males. A lack of mane in adult male lions is common and can occur based on the environment and climate where the animals live, injuries that occur when their manes are developing and other factors, he said.
Gnoske and Kerbis Peterhans also first reported on the damaged condition of the lions’ teeth in 2001, which might have played a partial role in why the animals shifted their focus to attack and eat humans. One of the lions may have sustained damage from a kick or a blow from a buffalo or zebra, which resulted in its inability to hunt normal prey efficiently, according to their research.
“We cannot claim that any single cause will guarantee that a lion will turn into a ‘maneater’, but it is clear that a variety of causes will increase the likelihood,” they wrote in the January 2001 study, including a prey-depleted landscape or predators that already have a taste for humans after scavenging corpses.
The lions had numerous dental injuries, including partially broken canine teeth, which allowed layers of hair from their prey to build up over time.
For the new study, Gnoske and Kerbis Peterhans carefully removed some of the hairs. The team focused on four tiny individual hairs and three hair clumps, all of which were well over 100 years old.
Study coauthors Ogeto Mwebi, a senior research scientist at the National Museums of Kenya, and Nduhiu Gitahi, a researcher at the University of Nairobi, carried out a microscopic analysis of the hairs. Then, de Flamingh led a genomic investigation of the hairs with study coauthor Ripan S. Malhi, a professor of anthropology at University of Illinois Urbana-Champaign.
The combined efforts opened a treasure trove of data about the lions’ prey as well as about the predators themselves.
The genetic analysis focused on mitochondrial DNA, or mtDNA, which is inherited from the mother in humans and animals and can be used to trace matrilineal lineages. Hair preserves mtDNA well and protects it from contamination, de Flamingh said, and mtDNA is also more abundant in cells than other types of DNA.
“We were even able to get DNA from fragments that were shorter than the nail on your pinky finger,” de Flamingh said.
Hairs from the lions show that they shared the same maternally inherited mitochondrial genome, which supports earlier beliefs that the two males were siblings. And lion hair trapped in their teeth suggests that the brothers were closely bonded and groomed one another, Kerbis Peterhans said.
Tracing links to prey
The researchers uncovered several surprises when they analyzed hair from the prey that the lions consumed.
The discovery of wildebeest DNA was unexpected because the closest population of the animals in the 1890s was at least 50 miles (80.5 kilometers) away — although the lion brothers departed Tsavo for about six months before returning to attack the camp again in November 1898.
“It suggests that the Tsavo lions may have either traveled farther than previously believed, or that wildebeest were present in the Tsavo region during that time,” de Flamingh said.
A single buffalo hair was also found using microscopy, and while buffalo are the preferred prey of modern Tsavo lions, the viral disease rinderpest devastated cattle and buffalo populations in the Tsavo region in the late 1800s. The highly contagious disease all but wiped out cattle and their wild relatives, including Cape buffalo, Kerbis Peterhans said.
“Patterson kept a handwritten field journal during his time at Tsavo,” Kerbis Peterhans said. “But he never recorded seeing buffalo or indigenous cattle in his journal.”
Meanwhile, the researchers are being careful and respectful of the human hair uncovered during their study, which they declined to describe or analyze to predict ancestry or ethnicity.
“There may be descendants still in the region today and to practice responsible and ethical science, we are using community-based methods to extend the human aspects of the larger project,” the authors wrote in the study. “The anthropological methods require discussions with local institutions and groups about the project as well as reporting the detailed human colonial history of this geographic region, which is beyond the scope of this current study.”
The team has a plan to work with the local community to see how it would like to proceed with studying the human hairs and tracing their genetics, Malhi said.
Reconstructing a predator’s timeline
The genetic technique developed during the research could be used to study the contents of broken teeth from ancient carnivores, opening up a new way to piece together the past, Malhi said.
Love Dalén, a professor of evolutionary genomics at Stockholm University, considers the technique “quite ingenious.”
“We’ve known for some time that it’s possible to get dietary information by extracting DNA from dental plaque in ancient teeth,” said Dalén, who wasn’t involved in this study. “But no one has thought to instead use hairs in carnivore teeth as a source for DNA.”
Microscopy work to identify more individual hairs from within the lions’ teeth is underway.
“In the published literature at least, I don’t know that there are any individual lions in history to have had such a diverse and long list of prey species documented,” Gnoske said.
Future analysis of the layers of hairs will enable the team to reconstruct a partial timeline of the lions’ diet and determine when they began hunting humans.
“Layers in lower parts of the tooth cavity represent prey eaten earlier in life and layers at the top of the cavity are from recently eaten prey,” de Flamingh said. “This type of analysis can give insights into human-lion conflict, which is still impacting many communities in the region and broadly in Africa. For example, if lions begin by hunting wildlife but then start attacking domestic animals, and eventually turn to preying on humans, we can develop strategies and recommendations to reduce these risks.”
