There is a class of animals that never grow old

We're born, we grow, we age, and then we die. Well, maybe not all of us, according to a new study on the animals amongst us who, while they continue to grow older, don't deteriorate with age.

A new study out of Nature takes a comparative look at the life cycles of 46 different species (us included) and finds that not all species live by this pattern of decline that we do. In fact some, the hermit crab, for instance, seem to have turned the whole process upside down. Virginia Hughes at National Geographic explains:

Some organisms are the opposite of humans, becoming more likely to reproduce and less likely to die with each passing year. Others show a spike in both fertility and mortality in old age. Still others show no change in fertility or mortality over their entire lifespan . . .

What the new study didn't find, notably, is an association between lifespan and aging. It turns out that some species with pronounced aging (meaning those with mortality rates that increase sharply over time) live a long time, whereas others don't. Same goes for the species that don't age at all. Oarweed, for example, has a near-constant level of mortality over its life and lives about eight years. In contrast, Hydra, a microscopic freshwater animal, has constant mortality and lives a whopping 1,400 years.

There's some interesting implications for both how we think about aging and evolution. You can read the whole thing here.

Image: Polinesia.