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The current explanation for why evolution hasn't removed aging from the equation is that aging only becomes a problem after you're all done having children. When you can't produce offspring, evolution is done with you. (Why you stop reproducing at all is another question entirely). But evolutionary biology researchers Paul Nelson and Joanna Masel at the University of Arizona say it's more fundamental than that: aging is the price of admission into the multicellular organisms club.

The problem comes down to the two things that happen to aging cells: they either slow down or speed up. You can see cells slow down as you go gray, when your hair cells stop producing pigment; and as you get wrinkles, when your skin stops producing the collagen and elastin that keep it smooth and hydrated. That's the kind of aging we're all accustomed to.

When cells speed up their growth rate, that's when people get worried. That can cause cancer cells to form. But despite how scary the C-word can be, cancer cells are just as much a part of aging as gray hair or wrinkles. It's just when they cause symptoms that they become a problem. For example, half of men over the age of 60 have prostate cancer, but it usually doesn't develop into anything harmful and most end up dying of some other cause.

Nelson and Masel modeled the evolution of the traits that make cells slow down and speed up, and what they found was pretty definitive. If you find a way to keep cells from slowing down — hooray, no more gray hair or wrinkles! — fast-growing cancer cells will take over and kill you. If you find a way to keep cells from speeding up — hooray, we found the cure for cancer! — sluggish, poorly functioning cells will accumulate and kill you.

"Aging is mathematically inevitable — like, seriously inevitable," Masel said in a press release. "There's logically, theoretically, mathematically no way out." Being multicellular means your cells will compete with each other. Throw off that balance, and you make things worse. We can lengthen human life, but we can't stop death, and that makes it even more important to embrace the time you've got.

To get to the bottom of getting older, check out The Longevity Book: The Science of Aging, the Biology of Strength, and the Privilege of Time by Cameron Diaz. We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.