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Princeton lab’s research on elephant tusklessness brings public attention to human impact on evolution

<h5>Professor Shane Campbell-Staton and team taking samples from a tranquilized elephant in Gorongosa National Park in Mozambique.</h5>
<h6>Courtesy of Rob Pringle</h6>
Professor Shane Campbell-Staton and team taking samples from a tranquilized elephant in Gorongosa National Park in Mozambique.
Courtesy of Rob Pringle

More elephants in Mozambique are being born without tusks. An ocean and thousands of miles away, researchers at Princeton wanted to understand why.

“It started after a 3 a.m. YouTube binge,” said Shane Campbell-Staton, assistant professor in the Ecology and Evolutionary Biology (EEB) Department, talking about his research in Gorongosa National Park, which has been covered by The Atlantic, the New York Times, and “The Daily Show” with Trevor Noah. 

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“I came across this video that was done by the Howard Hughes Medical Institute about the tusklessness of elephants of Gorongosa,” Campbell-Staton explained. 

Survey data from Gorongosa National Park in Mozambique showed an increase in the trait of tusklessness following the Mozambican Civil War, during which those elephants without prized ivory tusks were more likely to survive poaching. Intrigued, Campbell-Staton sent some emails and was put in touch with Robert Pringle, a professor in the University’s EEB department. Pringle was set to travel to Gorongosa in the upcoming summer of 2016.

Campbell-Staton and his friend Brian Arnold, a Schmidt DataX fellow at the University, decided to join Pringle in the mission of investigating the genetics behind tusklessness. 

As an evolutionary biologist, Campbell-Staton studies how animal traits are affected by human interactions with the environment. 

“One of the most profound things that we have found in contemporary biology is that evolution can happen very quickly,” he explained. “I think that fundamentally changes our understanding of what the process of evolution is.”

Pringle emphasized that studying evolution on a short timescale isn’t easy; it requires creativity and an ability to examine whole systems.

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Campbell-Staton has a team to help him. He’s the Principal Investigator of the Campbell-Staton Group, a laboratory he started building at UCLA that moved to Princeton University last summer. 

Campbell-Staton emphasizes science communication in his lab. 

“Sharing what we find in the lab and what we find in the field is really important to me,” he said. “Bringing evolution and biology into the mainstream, making it a natural part of everyday conversation, is my ultimate goal.”

True to this mission, the team’s research on elephant tusklessness has certainly reached a large audience.

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Trevor Noah and Ronny Chieng of “The Daily Show” recapped the study’s findings in a segment of the show in October 2021. The two gave their own comic interpretations of the results.

“A new study out of Mozambique has found that elephants in one park have been evolving to lose their tusks,” said Noah. “In fact, in the year 2000, there were three times as many tuskless female elephants as there were just 30 years earlier. Which makes sense. Elephants don’t need tusks anymore. We have can openers now.”

“Being able to avoid poachers is great news for elephants. Except for the elephants who just graduated from dentist school — I mean, there goes their future,” Noah continued.

“Hearing Trevor Noah talk about the research on Comedy Central, that was probably the weirdest thing. But it’s pretty cool. I’m happy that evolution is able to cross barriers into popular culture like that,” Campell-Staton said.

Pringle is also happy with the media attention. 

“It’s bringing knowledge to people, and I think that’s fantastic,” he said.

The path to producing and publishing the research certainly wasn’t always easy. Looking back, Campbell-Staton recalled how the research did not go exactly to plan when they arrived in Mozambique.

They originally wanted fecal samples to extract DNA from, but they couldn’t just pick up samples they found around the park. In order to know if a sample came from a tusked or tuskless elephant, they had to actually witness an elephant excreting it.

Yet, Arnold said, for the first few weeks they were there, they didn’t see a single elephant. He didn’t expect the large mammals to be so hard to spot, assuming they’d be able to gaze across the savannah with ease. Yet, the aptly-named “elephant grass” that covers the park can grow up to ten feet tall, inhibiting their view.

Luckily, they were able to team up with a group of researchers who were tranquilizing elephants for a tracking project, and secure blood samples from the tranquilizations.

Campell-Staton said they used those blood samples to sequence genomes from multiple female elephants. Every elephant, just like humans, has a unique genome resulting from the mixing of two separate and different genomes from their biological parents, as well as mutations, or changes to their DNA.

If this mutation is passed on to their offspring and creates a different set of instructions, like not instructing the elephant’s body to build tusks, eventually its frequency in the population can change, which means that evolution is occurring.

Now that Campbell-Staton had found his source of DNA, it was time to analyze it.

“We had several matriarchs, from different families across the park. About half of them had tusks and half were tuskless,” Campbell-Staton said.

They used that “genomic data to search for signatures and selection … to search for regions of the genome that differ between tusked and tuskless females,” he explained.

In addition to differences between tusked and tuskless elephants, they were looking for signs of other recent evolution; if one mutation increases in frequency very quickly among a population, often mutations located nearby to it in the genome do as well.

“We have found these candidate regions of the genome, but we have not found the specific allele or alleles that … may cause tusklessness,” Campbell-Staton said. An allele is a particular form of a single gene — for example, one allele may have the DNA for brown eyes, while another allele of the same gene would encode for green.

The researchers think it might be possible that the elusive “tusklessness gene” is lethal to males; this could occur if the gene for tusklessness also has other impacts that are essential for survival and resides on the X chromosome. Given that female elephants have two copies of the X chromosome and males only have one, females could compensate for one dysfunctional copy of the gene, while males would be out of luck.

Tuskless mothers have more female offspring than one would expect: survey data shows that about two-thirds of their offspring are female, which Arnold explained could be evidence that they harbor a mutation that is lethal to males.

Arnold noted that, while they have some candidate genes that could be responsible for tusklessness, the genomic data still requires validation. 

“This is a common theme in many genomics projects,” he said. “Research never ends.”

Campbell-Staton explained that the group is looking to expand its research with more samples and analyses.

“We’re also sort of branching out and looking at other populations to ask how broad the patterns we see in Gorongosa are,” he said. He explained that the group plans to do work in South Africa, northern Mozambique, and potentially other places in Africa, in order to draw comparisons across several populations.

However, the ongoing COVID-19 pandemic has disrupted the group’s plans, given restrictions on travel. 

“We will stay flexible based on what happens with variants and what travel restrictions get put in place. And, of course, the recommendations of the University,” Campbell-Staton continued.

Though the research continues, Campbell-Staton and his group have already succeeded in bringing mainstream attention to the science of evolution. He hopes that when people hear about the work they’re doing, they’ll understand humanity’s impact on other species differently. 

“I think that when most people think about humans, we somehow think of ourselves as disconnected from the natural world, or disconnected from the process of evolution. Which is not true at all,” he said.

Humans, he added, are not detached from nature, but rather intrinsically involved in ongoing natural processes, from our own species’ evolution to others’.

“Evolution is always a foundational part of who we are, and where we come from, and where we’re going,” Campbell-Staton said. “It’s also a foundational part of how we impact the planet, and the species that live in and around and among us.”

Madeleine Lausted is a Features staff writer and a writer for "Daybreak" in the Podcast section. She can be reached at mlausted@princeton.edu.

Paige Cromley is a staff writer for the Features, News, and Prospect sections. She can be reached at pcromely@princeton.edu.

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