Darwinism explained.

OK, Darwinism for Dummies. Just lately we have had a lot of little black fruit flies in our kitchen. Especially in the morning when I go in, there are a lot flying around or just sitting.
So I get a small towel and flick them out of existence. Or as many as I can. But there are always more.
A large area of our kitchen is white - the door frames, refrigerator and cabinet doors. So the little black flies are easy to see and to dispatch, if they land in those areas. But, some of them, maybe even the majority, I really don't know, land on other surfaces and are more difficult to locate.
So my thought is this, if I am successful in killing the flies that land on white surfaces, but not those that land on other areas, will we end up eventually only with flies that land on dark surfaces?
It makes sense. A male fly that for some reason only lands on dark surfaces will be more likely to survive, and will meet a female who also only lands on dark surfaces. As after several generations these will be the majority, at least in my home. Their offspring will be more likely, just more likely, not completely, to have baby flies that will be more likely to land on dark surfaces.
After some time - a hundred generations? A thousand? Who knows. But at some point we will have "bred" flies that only land on dark surfaces.
And that my children is how Darwinism works.