National Geographic Magazine November 2024

The curious case of the tigers who changed their stripes

In 2014 just four tigers remained in India’s Similipal Tiger Reserve. The only male, T12 (pictured), was born with a rare genetic mutation that left him with a predominantly black coat. As T12 helped repopulate Similipal, his dark coat showed up in his offspring—raising serious concerns over inbreeding.

Photograph by Prasenjeet Yadav

A century ago, India’s tigers were on the brink of extinction. Slowly, their numbers have rebounded. But that ecological success has prompted a dire problem—and a race to save many of them from genetic collapse.

Story, photographs, and video by Prasenjeet Yadav

September 15, 2025

It took 50 days of searching before the jungle revealed its biggest secret to us. Fifty days of jostling along gravel roads in the Similipal Tiger Reserve, in India’s eastern state of Odisha, scanning between trees in the semi-evergreen forest, hoping for a glimpse of an elusive tiger called T12, whose striking appearance has made him a symbol of a population at a perilous crossroads.

My partner in the quest, Raghu Purti, a staffer with the regional forest department, had never set eyes on T12. Most of his colleagues had only ever seen the tiger in images from camera traps set up to study animal movements throughout the reserve. But actually laying eyes on Similipal’s tigers lets forest officials look for physical ailments that cameras may not capture—and also provides a reminder that there’s a living, breathing purpose to the countless hours they spend patrolling in the sweltering heat. A documented sighting of T12 would be particularly valuable, since the reclusive 10-year-old tiger—the eldest male in Similipal—was right then at the heart of a plan to ensure the survival of future generations.

(Tiger photos)

It was late in the afternoon of day 50 when, in the blink of an eye, a dark shape dashed out in front of our pickup truck. I slammed on the brakes. Ahead of us, spanning the width of the road, an enormous tiger stared back at Raghu and me. It was an older male—clear from its size—and it had exactly the strange, distinctive coat we’d been looking for.

“It’s black,” Raghu said, in an insistent whisper. He pointed excitedly and repeated himself. “It’s black!”

(Here's how Yadav tracked a rare tiger for 120 days to get the perfect cover shot.)

Close to half the tigers in Similipal carry the genetic mutation that causes pseudo-melanism, including this cub—a descendant of T12—awkwardly walking across a stream in the reserve to cool off.

Photograph by Prasenjeet Yadav

The tiger, T12, had dark fur that draped over him like a ragged cloak. Slivers of orange peeked through along his body, with thicker patches appearing on his face and front legs. This uncanny widening of a tiger’s black stripes, a rare genetic mutation known as pseudo-melanism, is shared among roughly half the 30 or so tigers that roam the Similipal reserve. And it’s an indicator of a conservation success story facing a potentially catastrophic complication. Because while the number of tigers in Similipal is more robust than it has been in decades, the reserve is geographically isolated from other tiger populations—a tiger island, so to speak, with a dangerously dwindling gene pool.

But during the weeks that Raghu and I scoured the area for T12, work was under way elsewhere to find him a suitable mate. It was a crucial step in a targeted breeding program years in development, a mission shared between conservation agents and a team of groundbreaking molecular ecologists and genetic experts all working to save the tigers of Similipal from inbreeding themselves out of existence.

In many ways, India’s tigers have faced the same challenges as big cats throughout the world have, hunted to near extinction by trophy hunters amid relentless habitat destruction and fragmentation. In the 1970s alarm over the iconic species’ decline prompted the establishment of a state-run reserve system. But the reserves lacked coordinated monitoring and enforcement until 2005, when India created a dedicated central agency, the National Tiger Conservation Authority (NTCA), which today hires and trains rangers, manages scientific oversight, and guides habitat preservation across 58 reserves.

To break the cycle of inbreeding at Similipal, forest managers, working with genetic researchers, identified female tigers in the district of Chandrapur that had the potential to be promising mates for Similipal's males. Jamuna was the first Chandrapur tigress to be tranquilized and translocated.

Photograph by Prasenjeet Yadav

A key concept underlying the reserve system is that tigers are typically able to travel between protected areas using what are known as natural corridors—patches of connecting forest and other prey-abundant lands. There are a number of benefits to these corridors, but the most important is that they encourage breeding among neighboring tiger populations, improving genetic diversity. Similipal, at a little over a thousand square miles, is one of India’s largest reserves, and its closest neighboring ones—Satkosia to the southwest and Sundarban to the east—are both more than a hundred miles away, which isn’t too far for a tiger to walk.

But there are no tigers left in Satkosia. And no adequate corridor connects Similipal and Sundarban. The land between them is mostly urban or agricultural—Kolkata, its suburbs, and a vast area of rice fields—with very little forest cover, which is where tigers prefer to stay hidden. Dozens of towns and villages separate Similipal from its two neighboring reserves as well. For tigers, there is just no easy way in or out of Similipal.

When the NTCA surveyed wild tigers across India in 2006, the tally was roughly 1,400 animals—down from an estimated 40,000 a century before. In Similipal, the population bottomed out at just four tigers, in 2014, only one of them male. But in 2015, a year or so before he died, the male fathered T12, with his strange, predominantly black coat. And T12 has since fathered male cubs of his own.

India’s tiger population has begun to rebound over the past 20 years, thanks in large part to the conservation work of the NTCA and forest officials. As of a 2022 estimate, the country is home to more than 3,100 tigers. And as Similipal’s population climbed slowly but steadily over the past decade, the growing number of tigers at first seemed like a microcosm of the national success story. Soon, though, the reserve’s managers began noticing more and more young tigers sporting the same dark coat as T12. The mutation, as far as both foresters and genetic scientists can tell, is harmless, merely a cosmetic oddity caused by a random and naturally occurring quirk of DNA.

But, experts say, it is also a tangible manifestation of a very real problem. If this mutation was able to pass so quickly through Similipal’s population, with all the tigers sharing very similar genetic makeup due to rampant inbreeding, then so too could more serious abnormalities. Now the task facing some of India’s foremost tiger authorities has shifted from recovering tiger numbers to breaking this cycle of inbreeding before it’s too late.

(How Prasenjeet Yadav faces danger with confidence.)

In the past century, deforestation and development have fragmented habitats and severed natural corridors that enabled breeding between tiger populations. Some reserves have maintained or restored these corridors, while others remain cut off.

Photograph by Prasenjeet Yadav

To encourage a steady flow among tiger populations, India has constructed elevated highways and wildlife underpasses, such as this one between the Pench and Kanha tiger reserves. Here, two tigers cautiously cross underneath National Highway 44 (also shown in the previous photo).

Photograph by Prasenjeet Yadav

Playing genetic matchmaker for tigers is tricky. In order to find the ideal breeding partners for T12 and his offspring, the would-be saviors of Similipal needed to understand the differences among not only the tigers that roam today but also the tigers of the past.

That’s what led molecular ecologist Uma Ramakrishnan, not long ago, into a dimly lit trophy room in a grand home in Akaltara, a small town in central India. Ramakrishnan, a National Geographic Explorer and the head of a lab at Bengaluru’s (Bangalore) National Centre for Biological Sciences, was invited there by Anupam Singh Sisodia, whose family had once held the role of chieftains across 51 villages and the surrounding forests and farmland, responsible for protecting the locals from dangerous wildlife. His family had done its share of hunting, and the room was full of mounted black bucks, sloth bears, and four-horned antelope collected between 1920 and 1970. But laid out on a table before

Ramakrishnan was a set of tiger pelts, their massive heads intact and seemingly snarling.

“Killing problematic tigers,” Sisodia acknowledged, “was more of a political necessity than a pleasure.”

A tiger relocation is approved only when the donor population can withstand losing a breeding-age female. That poses no risk in Chandrapur, where the number of tigers is booming and the big cats regularly leave the reserve in search of prey. Sometimes that means livestock.

Photograph by Prasenjeet Yadav

Since 2005, Ramakrishnan and her fellow researchers and students at the lab have been collecting samples of tiger DNA in order to build an extensive genetic map of the diversity among India’s tigers. She’s secured roughly 250 specimens from historic estates like the Sisodias’. She has plumbed taxidermy collections at sites like the Natural History Museum in London and ventured into Indian jungles to procure scat, blood, hair, and saliva from live tigers. All that evidence has given her critical insight into how the animals have changed over generations as they moved throughout the region.

Closely inspecting one of the tiger heads, Ramakrishnan slid her scalpel into the 80-something-year-old pelt. Practiced and precise, she sliced off a small piece. She slid the sample into a vial and held it up.

“This is the real treasure,” she said.

When Ramakrishnan first began building her DNA database, her goal was to answer questions about tigers that couldn’t be answered by observing them in the field. As their population was decimated, tigers lost not only territory but also substantial genetic diversity. Historical DNA offered important clues about what else might exist within the gene pool.

Molecular ecologist Uma Ramakrishnan (at left) studies DNA collected from tigers both living and dead, here with the help of Anupam Singh Sisodia, who inherited his family’s collection of hides. The data have helped officials find tigers with the best odds of breaking Similipal’s inbreeding cycle.

Photograph by Prasenjeet Yadav

Her research became ever more relevant in 2017 when the NTCA, alarmed by the dark-coated tigers in Similipal, asked her to formally study the reserve’s tigers. The forest officials clearly saw that the impacts of the reserve’s isolation were becoming measurable. They hoped Ramakrishnan could both verify the genetic culprit and help them find a solution.

Once she took a closer look at the animals sequestered within the reserve, Ramakrishnan quickly realized that the recessive pseudo-melanism gene was spreading through the population. The genetic isolation on display, she said, was a ticking time bomb—left unaddressed, it could prove devastating to the reserve’s tigers.

It’s impossible to know precisely what other maladies genetic mutations among big cats might introduce. But when Ramakrishnan and her colleagues analyzed a genetic mutation dataset for the closest available comparison—domestic cats—they found that these not-so-distant cousins faced issues like retinal atrophy, kidney disease, and hyperthyroidism. And with female tigers averaging litters of two to three cubs every two to three years, health issues can quickly and dramatically compound.

“We’re still trying to understand the full impact of this inbreeding,” she says. “But one thing’s for sure—there’s no upside to this kind of genetic erosion.”