Remember the story of the race between the tortoise and the hare? The hare is so certain of victory that he wanders off track. Meanwhile the tortoise, slow but determined, lumbers along steadily and steals the race.

It turns out that in reality turtles are also winners in the marathon race of life. Among the longest living animals on earth, some species of turtle have average life spans of over 100 years. According to the San Diego Zoo, one of their giant tortoises has been alive for nearly 170 years. How do they do it?

As most animals age, their cells eventually break down. For example, human chromosomes are covered at their tips by DNA sequences that protect them from damage. But each time cells divide, their chromosomes lose a bit of the protective sheath until eventually they are left unprotected. At that point, our cells begin to deteriorate, leading to death.

Somehow, turtle cells manage to delay the decay. One theory submits that at an early age turtles produce telomerase, an enzyme that prevents the chromosome protectors from shortening. Consequently, while turtles do age, their bodies don't break down at nearly the same rate that ours do. In fact, as they get older, some become even more reproductively active.

But this doesn't mean that turtles can live forever. For one thing, turtles are eaten by the millions each year, both by humans, and predators in the wild. But even without death by digestion, all turtles eventually die off. Still, in the long run at least some turtles still manage to outlast the hare, and just about everyone else.