Linus (after having been asked about cooperation in writing software): "I never actually though about how the kind of community works at all. Until people started asking me about it later on, like journalists started - how can this ever work? - (in a very doubting way, by the way). [...] these people who asked the questions, they were not exactly convinced that it could work at all. So I kind of had to rationalise, why the Linux kind of development does work. And I don't know if this answers your question, but I actually came to my private conclusion which is that it really is all about evolution. And what you find, whether you like it or not is that [...] you don't design software, you don't even know what it is the user wants. Most cases the user himself doesn't know what he wants [...] If you designing things and you don't know what you're designing for, the design simply cannot work [...] and it turns out that this is a problem that humanity has had forever"
In this video (around 0:36:00) :
Interactive linux kernel map.