Today’s oldest bats are not supposed to exist. Ounce for ounce and pound for pound, they are categorically tiny mammals; according to the evolutionary rules that apply across species, they should be short-lived, like other small-bodied creatures.
And yet, many of Earth’s winged mammals buck this trend, sometimes decades past their predicted expiration date. One species, Brandt’s bat, which weighs only four to nine grams as an adult – the whole weight of a quarter – has survived to age 41 in the wild, almost as long than a standard four-ton Asian elephant, and almost 10 times longer than its body dimensions might otherwise expect. “It’s just surprisingly long for their size,” says Jerry Wilkinson, a biologist at the University of Maryland. “Longer than any other mammal.”
No single factor can explain the astonishing longevity of bats. They are intelligent and collaborative, and their super-powered immune systems help them tolerate viruses that make other animals seriously ill, traits that undoubtedly help them survive.. But one of their most biologically elusive anti-aging tricks in the world is to simply delay aging for months each year.
As autumn plunges into winter, small mammals huddle in caves, trees and mines, folding their wings and feet dangling overhead. Their body temperature plummets, sometimes approaching the freezing point; their heart rate slows to a handful of beats per minute; they are barely breathing. “They basically shut down their entire body, dramatically reducing all of the functions that we typically associate with life,” says Aline Ingelson-Filpula, a biologist at Carleton University. Periods of hibernation like these have long been understood as near-suspended animation, used to conserve the body’s resources in times of great need. For bats, Wilkinson and his colleagues found that it could also significantly extend their presence on Earth.
Time, in itself, is not really what kills us; it is how we spend it that destroys us. For most creatures, the calendar of days and months progresses at the same rate as the internal process of aging. But bats, and probably other hibernators as well, are actually able to uncouple these clocks, advancing their organic only age when they are active and awake, even when their chronological watch is ticking. “Think of hibernators as just extinct,” says Babraham Institute biologist Hanane Hadj-Moussa. “They’re not as damaged as an organism that just has to deal with life.”
Many scientists view aging as what happens when the body accumulates the wear and tear of life – the costs of metabolizing food and burning daily energy needs, the accumulation of cellular waste. Hibernation puts an end to these tedious processes. The animals that handle it “do almost nothing metabolically and they’re very cold,” says Jenny Tung, a biologist at the Max Planck Institute for Evolutionary Anthropology. It’s calorie restriction and cryopreservation in one, a slowdown that preserves physiological battery life, like switching an iPhone to low-power mode.
Scientists were first informed of the idea that hibernation could be a way to temporarily delay death in the early 1980s, when a team of Harvard medical researchers found that Turkish hamsters that spent a particularly long period in a seasonal pseudo-sleep perished later than their peers. In the years that followed, researchers quickly identified several other creatures that belonged to the Wake Less, Live More Club. Among them were ground squirrels, bats, marmots and lemurs, all of which survive similar species that don’t hibernate, clearly suggesting that hibernators were “cheating the game”, says Gabriela Pinho, biologist at the Ecological Research Institute of São Paulo, Brazil.
But permanently nailing down hibernation as an anti-aging ploy is tough. If animals are confined in dens for months out of the year, they are also generally better hidden from predators and more sheltered from the elements. To confirm that these periods of dormancy were in fact, at the molecular level, pressing the “Pause” button on animals’ inevitable march to death, Tung told me, scientists needed a way to “start wondering what is going on in the cells themselves”.
This year, two groups of researchers, led by Pinho and Wilkinson respectively, published some of the most compelling data to date on this front, on yellow-bellied marmots and big brown bats. Both studies scoured the genomes of small mammals, looking for epigenetic changes — molecular punctuation marks that annotate segments of DNA, making them more or less easy to read. These marks mix and scatter as we age, and researchers have studied them closely enough to read their patterns, almost like tree rings, and determine how far our tissues have progressed along the path to old age. . When researchers then compare that with the actual number of years an animal has lived, they can get an idea of whether a creature is, molecularly speaking, particularly lively for its chronological age, says Danielle Adams, a biologist at the University of Towson who worked with Wilkinson. on big brown bats.
By inspecting the genomes of marmots and bats at different times of the year, Pinho, Wilkinson, Adams and their colleagues were able to show that in winter the biological aging of animals actually stopped, even though they were accumulating months of chronological time, and then quickly. picked up in the spring as they woke up. The differences in DNA changes were large enough between seasons to be visible “within six months in the same individual,” says Isabel Sullivan, who was part of Wilkinson and Adams’ team.
Hibernation, to be clear, didn’t just happen to fill nature with groundhogs and geriatric bats. Its main purpose is to save animals from almost certain death during resource-poor and often cold times of the year. “It’s a survival mechanism, you just have to take the next step,” says Liliana Dávalos, a biologist at Stony Brook University. Perhaps it was serendipitous that these freeze frames also double as a fountain of youth.
Humans have other ways of surviving harsh winters – we’ve never needed to hibernate to survive. But the prospect of mimicking the act still tugs on our brains. It could save time for emergency surgeries. This could enable far-reaching space travel, keeping astronauts alive until they reach their destination, while largely eliminating the need to pack tons of food. If longevity is also an advantage, some people would probably wait in line.
Still, “I’d be safe to say that if we hibernate, we might just double our lifespan,” Wilkinson said. Many species still hibernate and die at around the age that their body size would predict. And as cushy as hibernation may seem, it threatens to demand a tax. When inactive, animals’ brain function falters, their weight drops and their digestive tract shrivels. They almost cease all movement and their reflexes slow down, making them easy prey for predators that fall on them and increasing the risk of muscle atrophy and bone demineralization. The power of the immune system also decreases, making the bodies super susceptible to infections. (It’s one of the main reasons bat flocks have been wiped out in recent years by white-nose syndrome, a deadly fungal disease that hits hibernators hard.) Creatures that evolved to hibernate have also developed many strategies to counter its costs, allowing them to rebound each spring. Humans, however, did not, which means the toll would be that much heavier for us.
Even preparing for hibernation is difficult. In the fall, pre-hibernating squirrels and bears must eat each other in a diabetic coma to store several months of fat. Yellow-bellied marmots, which can hibernate for up to eight months of the year, only have “four to five months to double their weight and reproduce,” Pinho told me, condensing their most important tasks into the brief periods during which they’re awake. (Their offspring must also eat frantically soon after birth, or risk dying in their first winter underground.)
Nor can hibernation guarantee restful sleep. Most mammals have to wake up – usually once every two weeks or so – to dispose of waste, perhaps sip some water and, ironically, sleep. These alarm clocks are extremely expensive: “Each awakening of a squirrel consumes about 5% of the energy it uses during the entire hibernation season,” Ingelson-Filpula of Carleton University told me. The etiquette of torpor is also… different. Some male bats will wake up in the dead of winter to have sex with still-sleeping females, who may wake up weeks later to find themselves dragging a stranger’s sperm.
And then there’s all the FOMO. Hibernation “would be a way of looking at the world in a future time, and it’s kind of appealing to think about,” Wilkinson told me. “But then you lose the opportunity to see things now.” Tung, too, wouldn’t want to give up a chance to “watch my parents grow old or my kids grow up.” Hibernation could be thought of as getting as close to death as possible without completely succumbing to it. If that’s the price bats and groundhogs have to pay repeatedly to extend their years, maybe they don’t really live much longer.