Narrator: This is Science Today. There have been ongoing debates about human lifespan - one camp believing there's a fixed lifespan, another considering it as basically open-ended. At the University of California, Davis, James Carey, a biologist and demographer, says the way the argument is currently framed, if you don't believe there's a fixed life span, then it's as if you're advocating immortality.
Carey: So a more appropriate way to frame this argument, in my view, is "Is lifespan determinate?" Or is it indeterminate in the same way that there are some birds that lay one egg, whereas chickens can lay any number of eggs - indeterminate. And likewise, lifespan is not determinate, it's open-ended, it's indeterminate.
Narrator: Carey developed a new longevity theory in which longer life spans allow people to create stronger social bonds and to make the medical discoveries that eventually prolong life.
Carey: I have to believe that understanding basic aspects of human aging and how to control this will be discovered down the road.
Narrator: For Science Today, I'm Larissa Branin.