Everyone is a Choosing Agent

1 Humans deliberately choose attractive roses, sunflowers etc. for breeding, thereby preserving the genes that produce the attractive features. This is called artificial selection, it's something humans have known about since long before Darwin, and everybody understands that it is powerful enough to turn wolves into chihuahuas and to stretch maize cobs from inches to feet.

2 Peahens (we don't know whether consciously and deliberately, but let's guess not) choose attractive peacocks for breeding, again thereby preserving attractive genes. This is called sexual selection, and Darwin discovered it, or at least clearly recognized it and named it.

3 Small prey fish (definitely not deliberately) choose attractive angler fish for survival, by feeding the most attractive ones with their own bodies, thereby inadvertently choosing them for breeding and passing on, and therefore preserving, the genes that produce the attractive features. This is called - yes, we've finally got there - natural selection, and it was Darwin's greatest discovery.

Darwin's special genius realized that nature could play the role of selecting agent. Everybody knew about artificial selection,* or at least everybody with any experience of farms or gardens, dog shows or dovecotes. But it was Darwin who first spotted that you don't have to have a choosing agent. The choice can be made automatically by survival - or failure to survive. Survival counts, Darwin realized, because only survivors reproduce and pass on the genes (Darwin didn't use the word) that helped them to survive.

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4 Without any kind of choosing agent, those individuals that are 'chosen' by the fact that they happen to possess superior equipment to survive are the most likely to reproduce, and therefore to pass on the genes for possessing superior equipment. Therefore every gene pool, in every species, tends to become filled with genes for making superior equipment for survival and reproduction.

Sexual selection, breeding selection, and survival of the fittest selection.