Over the past decade, geneticists and biologists have learned more about our evolution than we ever thought possible. Not all of it is pretty. For example, the DNA in our cells is littered with huge stretches of repetitive, useless gobbledygook. Our chromosomes also harbor thousands of viral “carcasses,” baggage left by infections that our ancestors fought millions of years ago. Evolution has not perfected our species—far from it. The human body, wondrous and beautiful as it may be, is cluttered with glitches and inefficiencies, the messy byproducts of evolution’s creative process. Natural selection is a blind, groping process, one that frequently produces terrible problems in addition to workable prototypes. Some of our flaws are due to little more than a mismatch between the world we live in now and the world we evolved in. Our immediate ancestors spent several million years eking out a living on the grassy plains of sub-Saharan Africa, an environment that bears little resemblance to the ones most of us now inhabit. These unfortunates spent hours each day chewing tough roots, choking down leaves and stems, munching on tiny berries and gorging on rare windfalls of meat, bone marrow and worms. It was during this time that our body’s metabolic system, which determines how we derive energy from food, developed one of its defining features: We are built to pack on the pounds when food is plentiful, and we retain that weight when we are deprived of calories. This system made very good sense back then, but it has backfired now that we graze not on roots and grubs but on a veritable savanna of rich, calorie-packed foods. Because natural selection never rewarded will power, it’s no surprise that we have so little of it now. This is just one of countless examples of how poorly suited our bodies are to our current environment. We sprain our ankles, twist our knees and suffer debilitating back pain much more than we would have been able to endure in the unforgiving Pleistocene epoch. This is chiefly because we sit in chairs, wrap our feet in supportive shoes and generally construct our surroundings to be as smooth and gentle as possible, leaving our muscles and tendons weak in all the wrong places. All of these questions have a single, simple answer: Evolution does not make or have a plan. Natural selection can only work on the bodies we have, making slight tweaks and tugs through the randomness of mutations.

— Human body flaws from evolution  

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