Obesity is an evolutionary legacy, which is why it’s so hard to control.
I said a few weeks ago (before I was rudely interrupted by the swine flu epidemic) that I would try to explain why the battle against overweight is such a hard and so far losing one, for the species if not for the individual. It’s not rocket science. In fact, it requires only a few facts and a bit of basic Darwinian reasoning.
Suppose you are a typical early hominid—still basically an ape but one up on its hind legs—of three or four million years ago. Your struggle for existence plays out in a world of fluctuating environmental quality. Maybe you’re dazzled in the rainy season by berries and quail you can pluck off the trees or out of the sky. Or maybe you have three years in a row where the nuts are so abundant they’re rotting on the ground and you can pick up a duiker any night within a mile of your nest.
However, you don’t get fat. You don’t love food that much. You don’t like carrying around that extra weight. It slows you down on the hunt, makes you more attractive to predators, maybe even makes it harder to chase down a little romance. You’re outstripping the ape-man next door in the quest for reproductive success, and he’s bemoaning his blubber.
But then the dry season comes and there’s nothing but fibrous underground tubers and the occasional skinny snake. Or the fourth and fifth year are as cold as a cat’s butt and dry as an old bone. Your formerly chubby buddy is not a happy camper; he lives to eat while you ate to live. Svelte as he may look now, he is utterly miserable.
But you—you are starving to death. And your last thought on earth before you give up the Darwinian ghost (assuming you are evolved enough to think in words) is, “I shoulda had a spare tire.” Not only our weird Western cosmetic ideal but even our now-accepted health ideal would have put you at grave risk.
Years ago my colleague Peter Brown and I surveyed the literature on ideal bodies in cultures across time and space. In most cultures, Brad Pitt and Kate Moss would have gotten nowhere fast. In fact, they would have been pitied as poor slobs who couldn’t keep their weight on. The ideal body in cultures throughout the ages on all continents has been, in a word, plump.
Why would this be? Marjorie Whiting, a nutritional anthropologist, studied shortages in a representative sample of 115 preindustrial cultures in the worldwide range. She found that shortages were rare (every 5-10 years) in around 28 percent, occasional (every 2-3 years) in around 25 percent, and frequent in almost half. Shortages were mild in 36 percent, moderate in 34, and severe in 30.
For the same study, I did a little calculation that proved relevant. The cost of carrying out a pregnancy is estimated to be about 80,000 calories (kcal).
Except for the nobility and such, this was the routine of life before modern times. So the calculus is pretty simple: Plump up in a world of abundance, and take whatever disadvantage that entails, because it’s inevitably temporary. And when it ends, your excess blubber will save your life.
But you may have noticed that there is a slight problem. In our world today, abundance never ends. Gone is the saving grace of unavoidable starvation, when, willy-nilly, you drew down that bank account of fat. Self-starvation, a path that no sane hominid—or any sort of animal for that matter—would voluntarily choose, has become the only way to avoid plumping up and up and up.
So our genomes contain not one but many “thrifty” genes that drive us to save energy as fat whenever we can possibly do that, because our ancestors who did that survived and reproduced, while those who didn’t, didn’t, and their descendants—the Kate Mosses and Brad Pitts of our weird Western world—are few and far between.
As I write this, I’m on a plane again, and it so happens that there is an overweight going toward obese middle-aged woman (her BMI, I would speculate, is 30-35). At least she is probably paying for her first-class seat, while I was merely upgraded. She reached across me and grabbed three or four bags of peanuts and chips for every one I chose—they pour it on in first class—but as she did that she seemed to be in a better mood than I.
She’s obeying an evolutionary imperative. True, it no longer really applies, but because of the eons in which it did, it still feels damn good, whereas I have to fight the imperative with every miserable fiber of my being.