I have posted this on another forum where I mentor on Spirituality and I am posting here again.
When things like spirituality are no longer present in one's life, they may or may not stop looking for meaning. Meaning is an essential part of human psychology, though some feel the need for it less than others, and even a few seemingly don't at all. There also seems to be a trend that occurs: in the lack of a meaning of life, the brain tries to find one, because it sees a purpose for everything.
What this thread is to address is the most commonly assumed purpose of living associated with atheism, but is rarely consciously understood: survival. The survival of life is the most common thing that is subconsciously assumed to be the only purpose for survival. From this perspective, things like art, music and spirituality are considered to be mere psychological needs.
Though, to most it may seem like simply a depressing state of mind, it is hypothetically dangerous. Religion may have literally evolved physically because it supports clan efforts to make sacrifices for the group even when they may not recieve something in return. Due to this, they survived strongly as a group because they needed each other to watch out for each other. The only way they could sustain a tribe from a lack of morality in desperate times is fear of a diety, or promise of a better life, which only comes from religion.
If the purpose of life is simply to survive, then there's really no reason why I shouldn't lie, cheat and steal. My instincts tell me not to, but others may come to the conclusion that their instincts need to be overridden with "reason," and that their desires should be met by whatever means necessary.
A lot of this is subconscious, and it is part of why atheists won't succeed without first philosophizing the "whys" of life. Why not kill? Why not lie? Why not cheat? Why do any of these things if I'm not going to get something back, and especially if I'm not going to suffer consequences?