I was taught in school that evolution was a random process, and that natural selection is what drives evolution. The animals with the best traits are more likely to survive and pass on those traits. More and more though, it seems that evolution is more of an adaptive process than a random one. I keep seeing more and more examples of genetic changes being triggered by changes in the environment and other factors, and not just happening completely at random.
An example of this is lactose intolerance. Europeans have one of the lowest percentages of people with lactose intolerance because their ancestors have been drinking milk for thousands of years. Simply drinking milk caused the specific genetic change so they were no longer lactose intolerant. I can't think of many other examples right now, but another example is that some scientists think we became as intelligent as we are simply because we eat cooked food.
Personally, I think all of physics is perfectly balanced for producing and sustaining life, but we just haven't gotten to a point yet where we can understand or explain how this is possible. I think life is a naturally occurring phenomenon which happens given the right conditions. This is how I get around the argument that "life is too complex to have happened by chance" and throw out the idea of creationism.
More or less though, I'm an atheist more because of history than science. History can explain the origins of each religion, and how certain things influenced the development of said religion. It can show how peoples interpretations of religion have changed throughout time. The more I learn about history, the less convinced I am that there is a creator or higher being of any sort.
My views on religion aren't all negative. I think it's responsible for creating the world we have today. Religion gave our ancestors a reason to build the pyramids and all of the other grand structures that came with each civilization. And this helped us to develop engineering and science to give us the world we have today. They didn't build the Parthenon because they were bored.