How do new species arise?

Biologists have been working on this question forever. (Darwin, despite the title of his book, really didn't nail it down). Now the computer geeks are having a go at it. Network theory indicates geographically localized mating increases diversity, but this works against assortative mating (mating with genetically similar individuals). This clash of forces fragments species into new ones. It's a lot more complicated than that, but this is an interesting insight.