Narrator: This is Science Today. People can expect to live longer today than ever before. This is usually chalked up to better medicine and healthier living conditions. But according to James Carey, a professor of entomology at the University of California, Davis, we may have evolution to thank for our longer lifespans.

Carey: We developed this theory on the longevity…orientation toward this with humans. And so when we explore this we find that lifespan extension is what we call self-reinforcing. That is the greater the lifespan, the greater your health is and the better your health is more your life span and so forth.

Narrator: Carey says that longer lifespans allow people to create stronger social bonds and to make the medical discoveries that prolong our lives. He says it's these factors-more than diet and exercise-that will continue to extend the human lifespan.

Carey: There will be things like organ replacement and there will be disease cures. But I feel that down the road we'll have a basic understanding of how to arrest aging at some level.

Narrator: For Science Today, I'm Larissa Branin.