Almost 20 years ago I read Jacob Bronowski's "The Ascent of Man". That was a turning point in my life because it helped me to become more confident in my agnosticism/atheism. One of the topics (there are many) that he covers is that in humans it is our level of cooperation that sets us apart from other animals. I then realized that this has always been the basis of my morality. I realize that all organisms must struggle to survive and ever since I was really young I have never wanted to make things more difficult for any other individual.