We’re not alone in the animal kingdom in our pursuit of long life. Many diverse creatures have evolved ways to live longer, up to 500 years, and they all boil down to metabolism and DNA.
When your body breaks down food, it produces free oxygen radicals that damage DNA and cause mutations. These mutations accumulate and ultimately result in aging and cancer. Eating less is, so far, the best way we know of to extend life. But this “secret,” which we only recently uncovered, has actually been out for millions of years, and some animals have gone all out in their quest for immortality.
Of Mice (and Elephants and Sharks) and Men
The Naked Mole Rat lives an average 31 years, far longer than any of its rodent cousins, mostly because it processes energy slower and maintains a low body temperature (one of the few mammals known to do so). In fact, most reptiles (think Lonesome George the Galapagos tortoise) manage their century-long lifespan by being cold-blooded and not eating for months at a time.
The Greenland Shark has taken this phenomenon to an extreme. It lives in the frigid arctic waters and we have literally no idea what, or how often, it eats. But what we do know is that this mysterious shark is the world’s longest living vertebrate (i.e. all fishes, birds, reptiles and mammals), with the oldest caught specimen having lived a staggering 392 years old (though some scientists believe they could live to 500). Simply by staying cool and hungry, Greenland Sharks alive today are older than our founding fathers.
Mammals such as ourselves usually cannot be cold-blooded (with the aforementioned Naked Mole Rat being a stark exception). Yet some still manage to wrangle with the Grim Reaper.
Too Big To Fail
Elephants are the largest land mammals, meaning that their cells have to divide a lot. Every division increases a cell’s risk of accumulating some fatal mutation and becoming aged or cancerous. Therefore, according to “Prado’s law,” large animals like elephants would be expected to age especially quick and suffer from a high incidence of cancer. Yet remarkably they don’t.
Elephants and their cousins (the dugongs and manatees) have evolved numerous copies of the p53 and LIF genes (humans only have two copies, and those who have fewer suffer from all sorts of cancers). Those genes allow elephants to target and kill cells with DNA damage, effectively weeding out aged (known as senescent) and cancerous cells.
This adaptation likely came about when the ancient ancestors of elephants, no larger than a rabbit, began growing in stature and, in turn, suffering from more cancer. In another similar example, the capybara, the largest rodent, has evolved an incredibly powerful immune system to mitigate the cancer risk that comes with its unusual dimensions.
Scientists are already looking at ways to exploit these genes to extend human lifespans, yet, as always, delivering and integrating them into all of our cells is just as tricky as it sounds. In fact, the hypothesis of “antagonistic pleiotropy” has found that many of the genes that cause cancer in old age are actually essential for our growth and development when we are young. The cure to cancer, just like the drowsy elephant, will have to take its time.
Although a simplified analogy, the animal kingdom reminds us that being unnecessarily big is detrimental to health in more ways than one.
Looking Small, Thinking Big
It’s not only elephants and sharks who have something to teach. C Elegans, a tiny type of roundworm, was the first being to reveal its secrets to scientists. Over forty years ago, researchers found that feeding these buggers less, growing them in less oxygen to slow down their metabolism, or keeping them cold all dramatically extend their lifespans.
It all boils down to a molecule that is the worm equivalent of insulin. It seems (at least in worms) that insulin does more than regulate blood sugar -- it can speed up or slow down metabolism and cellular replication (thus allowing elephants and capybara to reach their enormous size). The slower these are, the slower we age.
Some believe that although humans are far more complex, the same principles may apply. The MILES clinical study is investigating whether the type II diabetes drug Metformin, which regulates blood sugar (like insulin), could extend the lifespans of non-diabetics.
If different creatures from across the animal kingdom all agree that metabolism is inextricably entwined with immortality, then perhaps the best thing we can do to live long is live healthily. Numerous studies have shown that eating less and exercising more is a sure-fire way to extend lifespan.
Maybe one day we’ll find that “fountain of youth,” miracle drug that allows us to eat like pigs but live like Greenland Sharks. Most likely we won’t. But in the meantime, those of us who aspire to live long will have to stay thinner than the elephant and more active than the tortoise. We may not have their remarkable adaptations, but we can still learn from their example.
By Adam Barsouk