I don't generally like to use the term Atheist to describe myself, because that denotes the disbelief in the existence of god or gods. This does not have to preclude any rational reason as to why someone chooses not to believe. In a general sense, the term atheist has become an umbrella term to also include people with a perceived rational thought process for rejecting the existence of god, religion, the supernatural, etc... I prefer to call myself a Nihilist or Materialist as it covers the bases of rational thought process for denial of the existence of god, the rejection of religion, and the idea that there is no meaning or purpose in life. My philosophy is live it up, because you're gonna die.
I also come from a religious background (raised in a Lutheran household), but I can't say I ever believed...in fact I found it all very disturbing and perverted even at a young age. What, with being told Christianity was good, the way, the light yadda yadda, and then being told that cults were bad and that their beliefs were silly. People, statistically, are going to take on the beliefs, religions, ideologies and so on of the people or culture they grew up with...if you were to have grown up in India you would have a greater chance of being Hindi than ever being Christian. You are taught at a very early age, and its hard to shake those beliefs, often to the point of missing the main points of trying to live a good life as a good person and taking on these fundamentalist stances on literal interpretations.
Even the Catholic Church acknowledges the existence of evolution to an extent. There is a clear evolutionary lineage of man from different forms of primates and genetics to help back it up. But in the end...does it really matter...its an argument in futility for those devout believers on both sides (though I will say I side with those with empirical data). My question is this...do you know every single process and ingredient that goes into a hot dog? does it still taste good (assuming you like hot dogs)? Then eat it and don't worry about it. Same goes for life in general...live it up and don't worry about how it came to be...you may find its made of pig guts.