In reference to your statement that given enough time, humans would develop into something different than the present form, one point is that there are apparently, as I've read, only a few genes different between gorillas and humans. In other words, that difference makes the difference. And -- no one know what the in-between is, or perhaps better put, how the genes developed from some "unknown common ancestor" to the gorillas, bonobos, monkeys, etc., despite their closeness of genes the gap is -- rather signifcant.
But we *do* know, in general, how genes change. They duplicate, then mutate. We even know specific mutations that occurred in the human line (concerning growth of the throat and head, mostly). We don't know for gorillas and chimps because those species are far less studied.