Working out of labs in Denmark, Norway, Greenland, the UK, and the U.S., the marine scientists relied on radiocarbon dating to determine the age of Greenland sharks and concluded that the oldest of the animals they tested had lived nearly four centuries (um…give or take about 120 years).

While not everybody buys the assertion, there is other evidence to support the inordinate longevity of these ice-water creatures. Greenland sharks, which are born roughly 42 centimeters long, are very slow growing, getting about a centimeter longer every year. Adults, meanwhile, can easily range from 400 to 500 centimeters (from 13 to nearly 16 ½ feet). Do the math and that can put the oldest at just shy of the half-millennium mark.

So, why are these fish so durable? It has likely to do, at least in part, with their frigid artic environment—which likely slows down both their rate of growth and their metabolism. The notion that metabolic rate is tied to longevity (the less robust biochemical activity is in the species, generally speaking, the longer the lifespan) is an idea that traces back to 1927, to a trio of lectures given by Johns Hopkins biologist Raymond Pearl at University College, London. “If the average rate of metabolism or of energy expenditure is high the duration of life will tend to be shortened,” he said.

The lectures became a now-classic book, The Rate of Living, which largely kicked off the study of biogerontology. Pearl called this energy expenditure “a measure of ‘aliveness’ or vitality.” Which, of course, suggests an awkward syllogism: The more alive a species is, the shorter its life.

The metabolic theory, in turn, dovetails with another: the notion that as energy expenditure increases, so do the amount of “free radical” molecules or reactive oxygen species—which can damage DNA and other cell components. That gives us a handy mechanism—oxidative stress—by which active critters hasten their demise.

But there’s one mystery that has yet to be resolved: How did sharks get their feral, voracious, never-resting street rep if, in truth, many of their ilk are—how shall we put this—metabolically slow?

After all, it’s not just the ancient Somniosus microcephalus (Greenland shark) that’s a lethargic swimmer. So, too, is the nurse shark, which basically treats the ocean floor as a giant La-Z-Boy, grabbing the occasional lobster or conch as it crawls by, and barely breaking a sweat. The nurse shark’s metabolic rate is a mere 18% of the mako’s—and the breed is flourishing.

My takeaway? Take a breather this summer. Bring out your inner lazy shark. Enjoy a quiet lobster at the beach and don’t rush home. Who knows? Maybe you’ll live longer.

This essay appears in today’s edition of the Fortune Brainstorm Health Daily. Get it delivered straight to your inbox.