Natural selection

Three plain facts are all it takes. Living things have more young than can survive. The young are not quite the same as each other. Some of those small differences help them live long enough to breed.

Put the three together and something follows whether you like it or not. The ones with the helpful difference leave more young. Those young carry the same difference. Next time round there are more of them. Do that for a long time and the species is not what it was.

Notice what is missing. No goal. No one choosing. The word selection makes it sound like somebody picks, but the only thing doing any picking is the world: cold winters, fast cats, other mates. A beetle does not get darker because it wants to hide. Darker beetles got eaten less, and the pale ones left fewer young.

This also explains the mess. A designer would not run the tube you breathe through across the tube you eat through. Evolution cannot start again. It can only change what is already there, a bit at a time, and every step has to work on its own. That is why eyes have a blind spot and why backs give out.

Speed depends on how hard the world is pressing. Moths in sooty cities went dark in a few decades. Bacteria meet a new drug and shrug it off within years, because they breed in hours and there are billions of them. The same process looks slow in elephants and fast in germs for one reason: how many goes it gets.

The idea travels further than biology, and that is where people get careless. Ideas, firms and habits do copy, vary and get filtered. But they also borrow from each other and change on purpose, which genes cannot. The shape of the argument is the same. The details are not, and the details are usually where the claim is being smuggled.