Just Growing Old

Why do we grow old in general? For much the same reason that blue jeans and bicycles are disposable: It is a corrosive world out there. In time, chromosomes fray like downtrodden cuffs, and proteins oxidize like the metal of handlebars and spokes. But this facile answer belies the existence of extraordinary variability in the rate at which organisms age, much of this demonstrably genetic in origin.

As a species, humans are remarkably well off as far as aging is concerned. Our 80 years double the life span of our closest relative, the chimpanzee, and among mammals only elephants come close. That alligators are granted almost 70 years on Earth seems unjust, but swans make up for this by exceeding 100 years, and if you want a companion ...

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