 And the answer is it really can't. There's a lot of things that are not apparent that natural selection is going to eliminate. You can do some reading on this on your own, but I think you'll find that that is true, that natural selection can only take out certain things that would make someone definitely weaker or whatever. And a lot of these mutations can be, as they would call, deleterious or they're negative, but they are not negative enough for natural selection to get rid of them.