Evolution's End

Still, some might argue that maybe the environment wasn’t always stable. The food has changed. Our genes are changing. But the Paleolithic was relatively the longest stable period for humans to adapt to. Nothing is perfect. Maybe the Paleo diet is as good as it gets. The problem with that thinking is this: Evolution does not progress linearly toward a destination, nor does nature select a species where each individual is healthy and long-lived. To win in the race of natural selection, you need to produce a lot of descendants who can live just long enough to make their own descendants. Every member of that species is just a breeding unit. “Live long and prosper” has nothing to do with it.

That’s one explanation for why we have not evolved to be immortal. Evolution favors fertility over longevity. Genes that help individuals reach childbearing age and have more descendants win the evolutionary race, even at the expense of negative consequences in old age. There is some evidence that one variant of a particular gene involved in Alzheimer’s disease provides reproductive advantages to young people. Interestingly, people who live beyond 100 years old don’t die for the same reasons as people who merely live to 80. It’s as if their genes have special protection against normal aging effects. One might argue that these are the people who really need to spread their genes around.

In Tempo and Mode in Evolution, published in 1944, the influential biologist George Simpson wrote: “The paleontologist … is like a man who undertakes to study the principles of the internal combustion engine by standing on a street corner and watching the motor cars whiz by.” Our body is like a car handed down to us. If you want it to run smoother, don’t fuss over what the last owner did. Instead, focus on learning the chemistry of fuel and what goes on inside an engine.