I find that many intelligent people have trouble coming to terms with natural selection and its ability to shape a population through evolution.

For them, here is a simple thought that gives some pause, inspires awe, and may shed some clarity: every living being descends from an unbroken tree of individuals so stunningly well-adapted that *every* single one of them, over 3.5 billion years of evolution, managed to have offspring before encountering death. Not one of your ancestors died before engendering a son or daughter. Not from war, not from famine, not from disease. Not even from an accident. Some of them came close, such as my great-grandfather, who died in war before his only son was born. But he made it --one act of passion and his genes made it to posterity.

Now imagine meeting a group of athletes, each of which came from a family, which, faced with one great race per generation, had never ever lost a race in 3.5 billion years (at anywhere from minutes to decades a generation, that's more than 175 million races). You would expect those athletes to be mightily well adapted to running. And indeed they would be. Not the first time around, since you can win a race with good luck. But with every passing generation, the less likely that chance could explain their continued success. And eventually, no one but the most fantastic racing families would be left.

Well, that's natural selection, in a nutshell.

Up to Science.