But there's something special about naked mole rats that Rüppell couldn't have seen. Similarly-sized rodents, under ideal conditions, can live for five years or less. The life span of a naked mole rat is about six times as long. Even into their twenties, they barely seem to age, retaining strong heartbeats, dense bones, and remaining fertile. Scientists have dosed them with all sorts of carcinogenic chemicals and radiation, but unlike every other mammal, a naked mole rat has never once been observed to develop cancer.

Until recently, what let the naked mole rats conquer cancer and live so long was a total mystery. But over the past few years, a handful of researchers around the world have uncovered strange mechanisms inside their cells that seem to be the basis for the animals' uncommon longevity. The scientists' ambition is lofty, but not surprising: they want to harness these discoveries to one day vanquish cancer and battle aging in humans too.

The goal of anti-aging research isn't to raise life expectancy from 80 years to 90 — but to slow aging down, so a 60-year-old can feel like she's 50

Modern medicine's greatest success has been defeating a wide variety of deadly infectious diseases, from smallpox to polio. But eliminating or reducing the risk of one disease has increased the risk of another one that hits people later on. "In the 20th century, we added about 30 years to life expectancy," says Jay Olshanksy, a public health researcher at the University of Illinois at Chicago who studies aging. "We've allowed people to live into their 60s, 70s, and beyond. But what we got in return was heart disease, cancer, stroke, and Alzheimer's. As a byproduct of our success, we got aging."

To some scientists, this suggests another strategy is necessary. "If aging is a risk factor for everything, why not go after aging itself?" he asks. The idea isn't simply to extend life, but to somehow extend healthy life by slowing the process of aging. For a perfect model of this, you could look to the naked mole rats: well into their eighties (in terms of their human age equivalent), they stay fit and sharp, with strong muscles, hearts, and cognitive functioning. They somehow compress all their aging into the last few years of life.

Many people are troubled by the battle against aging, and are especially concerned about the possibility that success in the field could lead to catastrophic overpopulation and economic collapse as people live ever longer. But Olshansky feels that our whack-a-mole approach to diseases — solving one so that another can bloom, instead of slowing aging itself — is already extending life for many people, but with a hugely negative consequence. "We end up producing the very thing we want least: an extended period of frailty and disability," he says. The goal of anti-aging research isn't to extend this period further — say, by raising life expectancy from 80 years to 90 — but to slow aging down, so a 60-year-old in the future can feel like she's 50.

Studying aging itself, instead of disease, can take a number of different forms. Research can exclusively involve humans: some scientists are looking at the genes of particularly long-lived people, while others are studying people with rare disorders that prevent them from aging normally.

LONG LIFE IS KILLING US In the 1900s, pneumonia and influenza were the leading causes of death among people in the U.S. As better treatments developed, people began living longer, leading to a rise in age-associated deaths caused by issues such as heart disease. — Heart disease

— Tumors, cancer

— Pneumonia, influenza

— Tuberculosis

Deaths per 100,000 people Swipe left on the graph to view more years Sources: Centers for Disease Control, American Lung Association

But a particularly fruitful pathway might be comparing different animal species — and trying to figure out why some age so much more slowly than others. "Understanding species' differences in aging is crucial to understand the basic process of aging and why we humans age the way we do," says João Pedro de Magalhães, a biologist that's studying aging at the cellular level in a variety of species at the University of Liverpool. "This is one of the greatest mysteries in biology."

Last year, the prestigious journal Science named the naked mole rat its vertebrate of 2013. That unlikely designation was mostly based upon a string of striking discoveries made by the husband-and-wife biologist team Vera Gorbunova and Andrei Seluanov, who have a colony of about 100 of the animals at the University of Rochester. "They're so much more interesting than mice. A mouse sits in a corner and eats," Seluanov says. "These are intensely social, highly intelligent creatures."

In the wild — the grasslands of Kenya, Ethiopia, and Somalia — they live in a society like ants or termites. A single female queen and a few males do all the breeding, while dozens of sterile working animals use their teeth to dig networks of tunnels in complete darkness. Others search for tubers, their main food source. They use certain chambers for defecating and disposing of their dead, and others for nursing. Vast colonies can hide under the surface, only breaching it to expel dirt in a small mound.

For the past five years, Gorbunova and Seluanov have tended a colony at Rochester's Hutchinson Hall, inside a room kept at 90°F and sealed by a thick metal door. The hairless rats scurry back and forth, squeezing past each other in a network of plastic tubes that look like an elaborate home gerbil habitat. They occasionally fight for social dominance, and at times even kill each other. But these wounds account for nearly every adult death that's occurred in the colony — old age hasn't killed any of them so far.

Gorbunova and Seluanov, who were both born in Russia and met during high school, have studied the biology of aging in human cells, mice, and other species, but first got interested in naked mole rats in 2005. At the time, virtually all animal-based aging research involved mice or rats, which live three to five years. "Everybody studies animals that are short-lived for longevity, because it's more convenient," Gorbunova says. You can tinker with the animals' biology — say, by altering a particular gene — and see the effect pretty quickly.

Upon hearing about these discoveries, most people ask the same reasonable question: can they be applied to cure cancer and slow aging in humans?

But when she and Seluanov compared the genetics of 30 different rodent species, they were struck by the huge range of lifespans within the group. In both rodents and other animals, size is usually a rough predictor of lifespan. Chipmunks, for instance, can live up to ten years. Chinchillas can last 17 years, while squirrels and porcupines can live for 24 or so. But the small, blind naked mole rats can live the longest — up to three decades.

So Gorbunova and Seluanov, along with a few graduate students, began growing naked mole rat cells in petri dishes, using samples sent over from labs where the animals were used in neurological research. They immediately noticed something weird. "The naked mole rat cells didn't grow in the same way as most animal cells," Gorbunova says. "Usually, if you culture cells, they fill up the plate. But the naked mole rat cells kept stopping when there was still lots of room left."

All healthy cells have a tendency to stop growing when conditions get too packed, a property called contact inhibition. Normally, in a petri dish, they'll grow to form a sheet before they stop growing, but won't grow on top of each other. But the naked mole rat cells didn't even form a full sheet — they seemed to be hypersensitive to getting crammed in. This was intriguing, because in humans and other animals, contact inhibition can prevent the uncontrolled growth of cancerous tumors: clusters of cancer cells will stop growing when conditions get too tight.

So Seluanov and Gorbunova tested this resistance, dosing the naked mole rat cells with chemicals that reliably triggered the formation of tumors in mouse and human cells. Nothing happened.

To probe the animals more deeply, the biologists established a colony of live ones in 2009. They found a supply of the exotic animals at Vanderbilt University, from a neuroscience researcher who was now wrapping up his project. Because the animals are so sensitive to cold, their graduate students had to drive them up to Rochester mid-summer in a van with the air conditioning shut off. "About an hour away from Rochester, they got pulled over by the police for speeding," Gorbunova remembers, "and they'd taken their shirts off to stay cool."

As they continued to investigate why the animals' cells wouldn't grow tumors, they saw something else weird in the petri dishes. "We noticed that there was a very viscous goo building up between the cells," Seluanov says. "I got obsessed with figuring out what the goo was doing."

Eventually, they identified the goo as a sugar called hyaluronan. Human cells also secrete hyaluronan — it acts as a lubricant and structural protein between cells — but the naked mole rats' hyaluronan molecule was different, about five times longer. To test whether the hyaluronan was involved in the cells' resistance to growing closely together, the researchers added an enzyme to the petri dishes that cut it down to normal length.

"All of a sudden, the cells could grow quite densely, just like normal cells," Seluanov says. Later, when the researchers altered the DNA of the cells — turning on genes that are known to trigger tumor formation in other species, and turning off genes that led to the production of hyaluronan, and implanting the cells in live mice — tumors formed. These were the first cancers they'd ever induced in naked mole rat tissue.

As detailed in a Nature study last year, they ultimately found that two short genetic mutations in the animals were responsible for the long form hyaluronan. It seems that receptors on the surface of the naked mole rat cells register its presence — and when they come too near each other, it sticks to the cells, signaling for them to stop growing and preventing tumors from forming.

The oldest cat ever was 38 years old. The oldest horse was 62. The oldest dog was 29, and the oldest human was 122.

"Evolution has generated a great deal of variation in how long species live. We know that a mouse, on average, lives about three years, and a whale — another mammal — can live 210 years," says Olshansky, the aging researcher. "How does this happen?"

For most species, the answer is straightforward: the more vulnerable an animal is, the shorter its lifespan. Species that are likely to be eaten, like mice, have to mature and reproduce within their first few years, because they can perish anytime.

Evolution provides powerful incentives for surviving those few years and reproducing: animals that do so pass on their genes. But after reproduction, survival doesn't matter — in evolutionary terms — so these species don't develop mechanisms that might allow them to live a long time. One analogy is a car: if you bought a junker that you knew would break down in 10,000 miles, it wouldn't make sense to invest in a high-end stereo.

But for animals that are protected from predators, the evolutionary logic works somewhat differently. "When an animal can survive for longer, there's a selection for genes that provide longevity, because they can provide a real advantage," Olshansky says. A creature that won't get eaten — whether because of size (like an elephant) or armor (like a tortoise or porcupine) — is likely to live longer, so can reproduce for many years. Each additional year of life increases the chance of passing on its genes, so there's a strong incentive to evolve mechanisms that allow for longevity. It's like buying a brand-new car that might last 200,000 miles — in which case it makes sense to invest in quality parts and accessories.