I’ve been wrestling lately with some extra pounds that have me worried—and are changing the way I worry about worrying. Why? Because I’ve just 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 [read my article on this here]. The book suggests that putting on weight signals the body that the world is safe and food is plentiful. (That’s the good news.) Alas, the bad news is that the population could now grow too rapidly and overwhelm the food supply; therefore, those extra pounds signal a good time for older folks like me to make room for the young. As in, die. Yikes! That’s, in part, why taking it easy and eating a lot doesn’t make one grow stronger like a redwood: Instead, everything falls apart, easing us out—for the good of the group. Meanwhile, vigorous exercise, near starvation, and plenty of worry signal the body that times are tough, too many people are dying, and we need to keep going, no matter what—for the good of the group. This “demographic theory of …