Planning on living to see 100? It's probably a good idea to eat right and exercise. But then again, maybe you don't have to. What about those people who eat, smoke and drink their sedentary asses into their 80s, 90s, 100s and beyond? SciAm's Katherine Harmon gives you the lowdown on why, when it comes to longevity, your genes may matter more than your lifestyle habits:

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