Agnostics and Atheists are not the same but they are similar. Atheists do not know of a God. Agnostics believe but are unsure. The above definitons are more accurate.
Evolution is held by some and maybe most atheists because they actually understand evolution when most Theists shun evolution not really trying to understand it. Evolution does not show how the universe was created or started. It shows how life progresses. Evolution is just a scientific theory that can be proven wrong but has yet to be. Atheists study evolution because it is more tangible then an invisible being. Believe it or not but a theist can believe in evolution, meaning he or she can believe in a creator and see life continuing through evolution. These concepts are not easy to realize until a person actually wants to understand. Understanding evolution with a biased opinion will further no understanding.