At a (November 1995?) speaking engagement, Adams, author of the Hitchhiker's Guide and Dirk Gently series of books, was asked about his religious convictions and replied that he was raised in a religious household, and while listening to a street preacher realized that it was all utter nonsense. He was an agnostic until eight years ago when he became a "radical atheist".
There's more to the story, as the original contributor found in an article about Richard Dawkins in the September 9, 1996 issue of The New Yorker. "Douglas Adams, a friend of Dawkins's [...] found the experience of reading [The Selfish Gene] 'one of those absolutely shocking moments of revelation when you understand that the world is fundamentally different from what you thought it was.' He adds, 'I'm hesitating to use the word, but it's almost like a religious experience."' The contributor reports that it was this event which likely led to Adams's atheism.
Also, Adams is interested in making a TV documentary series about evolution.
Adams is interviewed in the Winter 1998-99 American Atheist magazine. An excerpt:
Q: Mr. Adams, you have been described as a "radical atheist". Is this accurate?
A: Yes. I think I use the term 'radical' rather loosely, just for emphasis. If you describe yourself as 'atheist' some people will say, don't you mean 'agnostic'? I have to reply that I really do mean atheist, I really do not believe that there is a god, in fact I am convinced that there is not a god (a subtle difference), I see not a shred of evidence to suggest that there is one...etc., etc. It's easier to say that I am a radical atheist, just to signal that I really mean it, have thought about it a great deal, and that it's an opinion I hold seriously.