About three years ago the radio tag from a nine-foot great white shark was found on a beach in Australia, and the story went viral that this great white had met a greater white. Newborn sharks famously eat one another, but the washed-up tag suggested the practice continues as they grow (and it does). It’s a shark-eat-shark world—for sharks. Now, here’s what I didn’t know until I read Cracking the Aging Code: The New Science of Growing Old and What It Means for Staying Young, by theoretical biologist Josh Mittledorf PhD and science writer Dorian Sagan: Sharks don’t age. Like some trees, great white sharks get bigger and stronger and more capable of reproduction as the years go by. While mini-greats struggle to get by, truly-greats can have more and more offspring, for breakfast, forever. Now compare sharks to salmon born here in the Rogue River. The newly hatched salmon feast on bugs that feasted on the bodies of their parents. Once these young salmon reach a safe size, they leave the river and brave the Pacific, where they swim for years—showing no signs of aging—until it’s time to …