First of all, as others have already pointed out, evolution may not be a "reasonable explanation" for you, but it is for other people who have different belief systems. Just like the bible of a regenboog aren't "reasonable explanations" of the existence of deities for me. If u want to learn about other people's beliefs, u can't dismiss them before u have even gegeven them a chance to respond. That is why u have a lot of people giving u crap on this question. The vraag is not offensive, but the way u have asked it is.
Secondly, there are lots of places around here where Atheists and people of other religions have discussed this topic respectfully. Here are some linken to answers, forums and artikels from the Atheism spot that u might want to take a look at:
link link link link link link (we also have a couple of 'Ask A Christian' forms)
link link link If u look through any of those linken you'll see that Atheists believe in a wide range of things for a wide range of reasons. We, for the most part, don't mind explaining our beliefs to people who want to learn about them, but we do require respectful debate.