These events, small and large, limit the range of possibilities on which natural selection can act.

But I am saying that natural selection acting on genes is probably not the whole story.

Darwin knew that nature had to produce variations before natural selection could act.

At the same time, selection acts on female size in order to increase fecundity.

It was the beginning of his conviction that selection acted on groups, not only genes.

However, there were differences of opinion as to the variation that natural selection acted upon.

These interactions produce emergent properties upon which natural selection can act.

Over long periods of time, natural selection acts on these variations to evolve or change the species.

Without the ability to isolate alleles, selection cannot effectively act upon them.

An interactor is a part of an organism that natural selection acts upon.