Aging brings about a range of changes—often unwelcome—to our bodies: sagging skin, graying or thinning hair, and a decline in muscle strength and vitality. But aging also affects us on the inside, altering proteins and other biomolecules in ways that increase our risk of developing chronic diseases—such as cancer, Alzheimer’s, and diabetes —and raise the likelihood of death. “You live, and by living, you produce negative consequences like molecular damage. This damage accumulates over time,” says Vadim Gladyshev, who researches aging at Harvard Medical School. “In essence, this is aging.” Yet some species (including some humans) age more slowly and live long, healthy lifespans. Why is that?

Why Mammals Have Different Maximal Lifespans

Mammals, for instance, differ dramatically in their maximal lifespans—from the tiny forest shrew, which lives only one or two years, to the bowhead whale, capable of living for more than 200 years. Humans are also notable among primates for their comparatively extended lifespans, living twice as long as chimpanzees, our closest relatives. Larger species tend to have longer lifespans than smaller species. At an average of 100 tons, the bowhead whale is about 100 times heavier than the forest shrew. The African elephant, the largest land mammal, weighs more than six tons and lives up to 65 years.

Larger species’ longevity is usually due to their ability to resist stress and predators. However, size isn’t the only factor, nor is it always definitive. Bowhead whales are enormous—the second-largest living mammal—but their 200-year lifespan is at least double what you would expect given their size. Farther down on the scale, Brandt’s bat, which weighs 5 to 20 grams (0.17–0.70 ounces), can live for more than 40 years, and so can the naked mole rat, which weighs a mere 34 grams (1.9 ounces). Because birds and bats can evade predators by flying, they live longer than their small size would predict.

Researchers have compared 26 mammalian species with diverse maximal lifespans. These ranged from two years (shrews) to 40+ years (naked mole rats). The thousands of genes identified were related to the species’ maximal lifespans. The genes were either positively or negatively correlated with longevity. The disparities in species longevity raise two questions: First, from an evolutionary viewpoint, why do some species have long lives while others don’t? And second, what genetic and metabolic idiosyncrasies allow the long-lived species to live as long as they do?

The Energy Theory of Longevity

Scientists believe that the answer to the first question lies in the energy a species expends to prevent or repair cellular damage. “You want to invest enough that the body doesn’t fall apart too quickly, but you don’t want to over-invest,” says Tom Kirkwood, a biogerontologist at Newcastle University in the United Kingdom. “You want a body that has a good chance of remaining in sound condition for as long as you have a decent statistical probability to survive.” Researchers found that short-lived species tend to have a high number of genes involved in energy metabolism. In contrast, long-lived species tend to have fewer genes that are similarly involved, indicating that those with lower metabolic rates conserve energy over the long term.

According to this theory, a house mouse isn’t going to spend much energy on maintenance because its chances of survival are slim. A predator, such as a cat, is likely to catch the mouse quickly. As a result, the mouse ages rapidly. By contrast, long-lived mole rats spend most of their lives in underground burrows, putting them beyond the reach of most predators; this allows them to allocate their energy to survival, enabling them to live for decades. Whales and elephants are less vulnerable to predators (except for humans, of course) and are likely to survive long enough to benefit from better-maintained cellular machinery.

Genetic Tricks to Delay Aging

But the question that researchers most urgently want to answer is the second one: How do long-lived species manage to delay aging? Researchers have made some progress in deriving an answer. Long-lived species, they’ve found, accumulate molecular damage more slowly than shorter-lived ones do. Comparative genomic analyses identify genes and biochemical pathways associated with complex traits and processes. What are the particular signaling and metabolic networks that might play a role in regulating age-related conditions? Why have specific organisms benefited from using novel evolutionary strategies and genetic determinants of aging in different environments?

Scientists have identified several aging-related genes in mice, fruit flies, and worms. But they still don’t know whether these genes controlled lifespan variations during the evolution of species. Some tantalizing clues, however, have emerged. For instance, the naked mole-rat evolved unique mutations in a gene that confer cancer resistance. DNA repair genes in humans, elephants, and whales, such as those found in the bowhead, help reduce cancer incidence in these species. These genes also appear to be related to longevity.

The risk of cancer poses a significant challenge to increasing the lifespan of mammals. For instance, two of the longest-lived rodent species—the naked mole-rat and the blind mole-rat—have discovered a genetic trick that utilizes interferon secretion to induce cell death, thereby enabling them to combat cancer. They have a gene called TP53, which appears to help prevent cancer by suppressing tumor growth. Indeed, elephants, like blind mole-rats, benefit from similar genes, and humans, too, have a protective equivalent.

Mammals didn’t start living longer only in the last few centuries. On the contrary, evolution has produced long-lived mammals multiple times over millions of years. Among the oldest surviving mammals are bats, tapirs, monkeys, rhinos, horses, bowhead whales, and apes. Humans also enjoy a high ranking. As of 2025, Jeanne Calment, who died in 1997 at the age of 122, is recognized as the longest-lived human; however, some scientists speculate that humans may live up to 150 years or more. Each evolutionary experiment has involved trying out different genetic strategies, such as enhancing homeostasis (biological balance) throughout life or preventing cancer.

The “engine” of evolution is called the pluripotency network. That is, all embryonic or pluripotent stem cells can differentiate into various cell types in different parts of the body, such as the lungs, liver, or pancreas. “We discovered that evolution activated the pluripotency network to achieve a longer lifespan,” says Vera Gorbunova, a biologist at the University of Rochester. The pluripotency network enables the reprogramming of somatic cells—non-reproductive cells—into embryonic cells. Embryonic cells can more readily rejuvenate and regenerate by repackaging DNA, which becomes disorganized as we age.

The pluripotency network is “an important finding for understanding how longevity evolves,” says Andrei Seluanov, a researcher at the University of Rochester. “Furthermore, it can pave the way for new antiaging interventions that activate the key positive lifespan genes. We would expect that successful antiaging interventions would include increasing the expression of positive lifespan genes and decreasing the expression of negative lifespan genes.”

Establishing a link between gene expression and longevity requires more than simply identifying the genes involved or the actions they perform in the body. Scientists need to determine when these genes are activated—turned on—and at what times on a daily, monthly, and yearly basis. Circadian networks also play a role in controlling the lifespans of genes, specifically whether a particular gene’s expression is limited to a specific time of day, which may inhibit the action of that gene in terms of how long, on average, a species can live.

Researchers can determine when specific genes are activated by attaching chemical tags, known as methyl groups, to sites that regulate gene activity. Geneticist Steve Horvath of the University of California, Los Angeles (UCLA), and his colleagues have found that by assessing the status of a set of almost 800 methylation sites scattered around the genome, they can reliably estimate an individual’s age relative to the maximal lifespan of its species. This “epigenetic clock” holds for all 192 mammalian species Horvath’s team has examined so far. He surmises that by reviewing these methylation sites, he will be able to predict a species’ lifespan regardless of any particular individual’s age. This is an advantage in studying species previously unknown to science.

For longer-lived mammals, this means their genes remain active for a longer period. Put another way, their epigenetic marks degrade more slowly, causing their biological clocks to tick more slowly. For example, the longest-lived bats often have the slowest rate of change in methylations, whereas those of shorter-lived species change more quickly.

The Longest-Lived Species

Elephants

Since large size in mammals generally corresponds to a slow metabolic rate, it is hardly surprising that elephants have long lifespans. African elephantsare estimated to live up to about 74 years, whereas Asian elephants can live up to about 60 years. Elephants in both parts of the world also possess extra copies of the tumor-suppressor gene TP53, which may help them deal with DNA damage by clearing affected cells, allowing them to live longer.

Marmots

At the other end of the scale are yellow-bellied marmots, which weigh between 7 and 15 pounds and can live for 15 to 18 years. Natives of the United States and Canada, they spend almost half their lives hibernating, entering their burrows each year during September or October and remaining in them until May.

In the other months, marmots, which resemble ground squirrels, prepare for hibernation by fattening themselves on flowers, grasses, insects, and bird eggs. It is their long hibernation period that explains why they can live as long as they do. During hibernation, marmots alternate between periods of metabolic suppression, which last approximately one to two weeks, and shorter periods of increased metabolism, typically lasting less than a day. During metabolic suppression, the animals’ breathing slows, and their body temperatures drop dramatically, allowing them to use a minuscule amount of energy—about a gram per day. By saving energy, marmots can survive prolonged periods without food. Hibernation basically stalls the aging process.

A study of marmots in the wild shows that an antiaging effect kicks in when marmots are two years old, based on the date at which juveniles first emerge from their natal burrows. Researchers at UCLA believe that these hibernation-related adaptations—diminished food consumption, low body temperature, and reduced metabolism—are the reason why marmots outlive other animals of a similar body weight. The UCLA researchers speculate that the marmot may offer a model adaptable to humans, for example, to improve organ preservation for transplantation or to enable long-term space missions.

Bowhead whales

This 100-ton cetacean can live up to 200 years. It is one of the heaviest animals on the planet. Researchers studying its genome have discovered that this species possesses unique genes that aid in DNA repair and resistance to mutations that can lead to cancer. The bowhead whale’s cells were both efficient and accurate at repairing double-strand breaks in DNA—that is, restoring broken DNA so that it’s as good as new. And their cells do this more often than the cells of other mammals. It is thought that the whale’s relatively sluggish metabolism may also account for its longevity. These whales, of which there are now approximately 25,000, inhabit Arctic and subarctic waters. Research conducted in 2025 found that the bowhead whales may live as long as they do because they can repair detrimental mutations in their DNA, thanks to a protein (CIRBP). These mutations, if unchecked, can increase the risk of cancer and age-related diseases over time. Whales have 100 times as much CIRBP as humans do, which may explain why they live beyond the normal human lifespan. The researchers believe that their repair mechanism is enhanced by the frigid Arctic waters in which these whales spend their lives.

Bats

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