This ‘Clock’ Could Warn of Hidden Stresses to Animals, Offering a Long-Sought Signal That a Population Is Nearing Collapse The epigenetic clock measures biological age and could help scientists assess the health of polar bears, dolphins, baboons and other threatened creatures “while recovery is still possible” The epigenetic clock is emerging as a wildlife conservation tool. Knowable Magazine Key takeaways: Epigenetic clocks as a conservation tool Conservationists have been searching for a biological marker to hint that an animal population is in distress so that they can address warning signs before a collapse becomes inevitable. A recent preprint study used epigenetic clocks, a marker of “biological age,” to find that polar bear populations are aging more quickly than previous generations did, suggesting melting sea ice is taking a toll on their health. Wildlife conservation is a race against time—too often, a losing one. Typically, by the time scientists detect signs of species decline, populations have already collapsed. Genetic diversity is already depleted. Birth rates have plunged. And by the time these biological red flags are seen, the window for effective intervention has nearly closed. That’s what happened with the passenger pigeon: Once the most abundant bird in North America, it vanished in the blink of an ecological eye—wiped out by unchecked hunting and habitat destruction before anyone realized how fast the population was unraveling. The same story played out with the Chinese river dolphin, the Pyrenean ibex and the Caribbean monk seal. Silent declines went unnoticed for years until the tipping point had passed, leaving conservationists to document extinctions instead of preventing them. And the northern white rhino? By the time the world finally paid attention, the damage was irreversible. Poachers had reduced the species to two surviving individuals—both female. Determined to avoid more preventable losses, scientists have begun hunting for molecular warning signs that appear before populations spiral. But early leads, such as stress hormones and the length of the specialized tips of chromosomes—telomeres—have proved fickle, too easily swayed by the daily chaos of life in the wild. That’s why many scientists are now pinning their hopes on a novel tool called an epigenetic clock. This molecular timekeeper doesn’t keep time like a wristwatch, though. Instead, it measures “biological age,” a hidden ledger that can echo the calendar’s count but also offers a more nuanced reflection of how fast an organism is wearing down from stress, disease and environmental hardship. Epigenetic clocks work by analyzing patterns of chemical tags called methyl groups that get added to or subtracted from DNA at predictable sites across the genome as animals grow older. Some of these methylation signatures are remarkably stable and tightly linked to aging across many species. And, crucially for conservationists, they can be read from a simple tissue or blood sample. In the lab, researchers analyze skin biopsies from Lahille’s dolphins to measure DNA methylation patterns—molecular marks that reveal both true age and signs of accelerated aging. Oceanographic Museum Prof. Eliézer de C. Rios / FURG, Southern Brazil That makes epigenetic clocks especially valuable for elusive or long-lived species, where accurate age data are often missing. Wildlife biologists are already using these clocks to understand the age structures of animal populations, offering insights into their reproduction, survival and longevity. But the clocks hold deeper promise. When an animal’s biological age runs higher than its chronological one, it can signal physiological strain—a kind of molecular distress flare that may go off before any visible signs of problems. The potential for detecting accelerated aging before a population begins to visibly collapse is what excites Colin Garroway, an evolutionary ecologist at the University of Manitoba in Canada. “Almost everything else we have is a lagging indicator of species decline,” he says. “This is at least potentially forward-looking.” Garroway’s confidence in the power of epigenetic clocks took shape through a study of polar bears from the Canadian Arctic. In work now posted on the preprint server bioRxiv, which has not yet undergone peer review, he and his colleagues found that bears born in recent decades are aging markedly faster than those from earlier generations—their biological ages outpacing their chronological ones. The likely cause, the researchers conclude: Longer ice-free periods are stranding bears on land, cutting off access to the seals that form the core of their diet, ultimately sapping the fat reserves they need to survive. “The change is too fast and too significant for them,” says co-author Evan Richardson, a polar bear ecologist with Environment and Climate Change Canada, the government agency that partially funded the study. That burden is then evident in the telltale molecular marks on the animals’ DNA. Richardson hopes the findings will force the “harder discussions” around polar bear management. But beyond sounding the alarm for this one imperiled species, he and his colleagues are hopeful that the wider conservation community will embrace epigenetic clocks as a proactive tool to safeguard biodiversity—before the point of no return. As Meaghan Jones, a University of Manitoba medical geneticist involved in the research, puts it: “This is a way to monitor populations in real time and see how stress is impacting them while recovery is still possible.” Clocking in The idea of tracking biological age through molecular changes first gained traction in studies of human DNA. Beginning in the early 2010s, biogerontologist Steve Horvath—then at the University of California, Los Angeles and now with the anti-aging biotech company Altos Labs—identified dozens and later hundreds of sites in the genome where DNA methylation tags were predictably gained or lost as people grew older. He used methylation patterns to construct a statistical model that could estimate a person’s age, launching the first epigenetic clocks. Horvath’s clocks emerged as powerful health indicators, with individuals whose biological age exceeded their chronological one showing a higher risk of chronic illness or early death—and that same logic, outlined in the 2025 issue of the Annual Review of Public Health, soon found a foothold in wildlife biology, too. Wild wood mice are helping scientists at the University of Edinburgh uncover how environmental factors such as food shortages and parasite infections accelerate biological aging. suffolk_jim / iNaturalist In 2021, for example, a team led by Jenny Tung, an evolutionary anthropologist now at the Max Planck Institute for Evolutionary Anthropology in Germany, developed a baboon-specific version of the epigenetic clock and applied it to a wild population in Kenya’s Amboseli basin. The researchers found that males with a high dominance rank tended to be biologically older than their lower-status peers, even when their chronological ages were the same. It was a compelling demonstration that the clock could connect ecologically relevant pressures to accelerated aging in a wild animal. And contrary to what might be expected—that social success would track with better health—it revealed the biological toll of dominance. “Attaining and maintaining high rank is costly,” Tung says. Other studies linking life stressors to accelerated aging would eventually follow—Garroway’s polar bear work among the most prominent—but most early adopters of epigenetic clocks for wildlife biology focused on a more basic goal: filling gaps in demographic data. Traditionally, estimating the age of wildlife involves methods such as tooth extraction to count growth rings, which is labor-intensive and intrusive. Epigenetic clocks, in contrast, require a small tissue or blood sample, often obtainable through remote methods like dart biopsies. From there, researchers extract DNA and use lab methods to read the methylation patterns known to change with age. Then, they apply statistical models to compare the patterns with animals of known ages. Inspired by the work of Horvath and others, wildlife biologists began adapting epigenetic clocks for the animals they study: humpback whales, lampreys, sea turtles, salmon. Then, in 2017, Horvath secured a $1.5 million grant to build clocks for a menagerie of species. Lions and tigers and bears Horvath began cold-emailing field biologists, zoo veterinarians and wildlife researchers, inviting anyone with blood, DNA or other archived tissues in their freezers to join the project. “Whoever had samples became a partner,” he says. Specimens poured in—for nearly 350 animal species in total, representing 25 of the 26 known taxonomic orders of mammal. Horvath generated clocks for elephants, bats, zebras, monkeys, marmots, mole rats and more. From this, he and his global network of collaborators built a universal mammalian epigenetic clock, one that factored in each species’ maximum lifespan alongside observable shifts in DNA methylation over time. The result was a clock that could accurately gauge an individual’s age, both chronological and biological, from a DNA sample—not just in humans or lab mice, but in otters, opossums and Tasmanian devils, too. Horvath’s main aim was to explore how aging unfolds across the animal kingdom and what accelerates the process—potentially uncovering antiaging mechanisms that might be replicated pharmaceutically. But there were clear applications for conservation, starting with filling in missing details about survival and reproduction in the wild. In Alaska, for example, wildlife biologist Susannah Woodruff, then with the United States Fish and Wildlife Service and now with the state’s Department of Fish and Game, turned to the pan-mammalian clock to estimate the ages of the state’s polar bears. Working independently of the Canadian team pursuing similar questions, she and her colleagues first ran samples through this “universal” clock and found it performed reasonably well, producing estimates within a year or two of the bears’ true ages. “That’s pretty good,” Woodruff says. Building a clock tailored specifically to polar bears was better still. Doing that required getting blood samples from known-age individuals—something not feasible for every species—but in Woodruff’s case, she had access to nearly 200 such bears. And as a head-to-head comparison published in July showed, the bear-specific clock yielded more precise and reliable results, pinpointing age to within plus-or-minus nine months. Epigenetic clock studies show that polar bears born in recent decades are aging faster than earlier generations, likely due to shrinking sea ice that limits their hunting opportunities and erodes fat reserves. Susannah Woodruff Short of developing a bespoke species clock, the next best thing can be to adapt one from closely related kin. That’s the approach taken to study the Lahille’s dolphin by conservation medicine veterinarian Ashley Barratclough of the nonprofit National Marine Mammal Foundation in San Diego. This vulnerable subspecies of bottlenose dolphin is found off the coast of South America, with fewer than 600 left in the wild. Few have reliable age records. Barratclough and her colleagues first created a clock for the common bottlenose dolphin, using blood and skin samples collected from known-age animals maintained by the U.S. Navy. In collaboration with Brazilian marine biologist Pedro Fruet, Barratclough then applied the tool to the genetically distinct Lahille’s dolphin, filling in demographic black holes that, among other things, identified reproductive-age females, thus providing a focal point for conservationists to target in their efforts to rebuild the population. “For an endangered cetacean species like the Lahille’s bottlenose dolphin, every piece of demographic information is extremely important to understand the future of the population,” says Fruet, founder of the conservation group Kaosa. “And the epigenetic clock tool is helping us to refine and get estimates that we couldn’t otherwise.” Notably, in Brazil’s Patos Lagoon, where the true ages of some Lahille’s dolphins are known, the tool also revealed signs of accelerated aging, notes Fruet—a finding he fears may reflect the impact of pollutants from industry and agriculture, among other stresses. Barratclough has documented similar effects in the Gulf Coast of Louisiana, where dolphins exposed to oil pollution from the 2010 Deepwater Horizon disaster appear to have aged faster than their counterparts living in cleaner waters elsewhere. Conservation biologists use remote dart biopsies to collect tissue from Lahille’s dolphins, a vulnerable subspecies with fewer than 600 individuals left in the wild. The samples provide crucial data on their age structure and reproductive potential. Pedro Fruet / Kaosa Worse for wear As evidence grows that epigenetic clocks can not only reveal true age but also flag premature aging, researchers are beginning to probe how environmental hardships shape the tempo of aging in the wild. At the University of Edinburgh, for example, evolutionary biologist Tom Little and disease ecologist Amy Pedersen are experimentally manipulating factors such as food availability and parasite load in wild wood mouse populations, then tracking the epigenetic fallout over time. “If you look at the human literature, we’ve got all these things—diet, stress, infections—that we know influence biological age,” Little says. “But in wildlife, we just don’t know what environmental features drive animals to be gray before their time.” Such research, however, requires running large numbers of samples through expensive molecular tests, and a major barrier to wider-scale adoption of wildlife clocks remains cost. The most commonly used testing platform—the Horvath Mammalian Array, based on Horvath’s research, manufactured by the genomics giant Illumina and sold by the nonprofit Epigenetic Clock Development Foundation—runs about $200 per sample, which adds up quickly when trying to analyze dozens or hundreds of wild animals. “It becomes very cost-prohibitive, especially in my budgetary world,” says Aaron Shafer, a population geneticist at Trent University in Canada who is studying whether epigenetic clocks can reveal premature signs of aging linked to chronic wasting disease, a deadly neurodegenerative illness affecting deer populations across North America. Shafer is spearheading the development of lower-cost, custom-built tests to make the technology more accessible for conservation use. In parallel, Garroway and Jones, together with Levi Newediuk, a wildlife ecologist at Mount Royal University in Canada, have been working on ways to streamline the use of epigenetic clocks in wildlife research so it can be applied in more species and settings. They also want to drive home the relevance of epigenetic clock data to policy decisions by connecting biological aging directly to habitat degradation. In their polar bear study, for instance, the researchers didn’t just document faster aging. They tied those biological shifts to tangible environmental change. Bears born in recent decades, as Arctic temperatures have risen, showed clear signs of accelerated biological aging, the scientists found. And unpublished follow-up analyses indicate that the effect plays out unevenly across regions, shaped by the distinct ecological pressures faced by each population of bears. According to Newediuk, the trend was most pronounced around Hudson Bay, where seasonal sea ice breaks up earlier and forms later than it once did, curtailing hunting opportunities and limiting access to seals. In contrast, bears from regions with more stable ice, such as those living near the Beaufort Sea and around other parts of the high Arctic, are aging more slowly. The findings, in other words, lend weight to long-standing concerns that vanishing sea ice isn’t just threatening the bears’ hunting grounds—it’s quietly eroding their biological resilience. “They’re in trouble, for sure,” Newediuk says. Fortunately for the threatened wildlife, accelerated aging isn’t necessarily a one-way street. As Tung’s investigation of baboons has shown, it can be slowed—potentially reversed. Tung found that when male baboons lost dominance rank, their epigenetic clocks seemed to slow down. In a couple instances, biological age even ticked backward as males fell in social status, despite the passage of time. That means the rate of aging is “not necessarily a fixed trait,” says Tung. And if it can be delayed in baboons, perhaps it can be rolled back in other species as well. “It opens the door to that possibility.”Knowable Magazine is an independent journalistic endeavor from Annual Reviews. Get the latest Science stories in your inbox.

The epigenetic clock measures biological age and could help scientists assess the health of polar bears, dolphins, baboons and other threatened creatures "while recovery is still possible"