Well, you're leading on to a separate discussion, my main point was that atheism is not a belief system on par with religion. Judaism is an alternative to Christianity, but atheism is not, in the same way that being a fan of the Patriots is an alternative to being a fan of the Steelers, but not giving a crap about American football does not make one just as much a fan. There's no real word for someone who doesn't give a crap about American football, but I suspect that has to do with the fact that people aren't elected to public office based on which football team they support, and that it would change if that were the case.
I don't see why morality needs to have some absolute source. Morality is a social consensus. Both religious and atheist people get their morals from the same place; other people and their own human nature. Morality and reproductive fitness aren't equivalent at all, you're looking at two different levels. People are moral, genes are amoral; neither moral or immoral. It's just a simple byproduct of economy of scale, that it is advantageous for humans to work together. It's easier for friends to help each other move apartments than it is for each one to move on their own, you're safer and less sleep deprived if you and some friends take turns standing on watch than if you tried to all be responsible for your own security, etc. etc. Yeah, there will be bad people who exploit these relationships for their own benefit, but that will often mean that they won't get these benefits in the future. Humans have long memories and extensive networks of gossip, such that a bad reputation can quickly ruin a life.
A person doesn't have to be selfish to benefit their selfish genes, in fact it definitely pays to be a well liked, reliable, and reputable person. Natural selection doesn't care how the job gets done, just that it gets done, so we have a slew of emotions tuned exactly to lubricate social co-operation such as trust in a person, guilt at betraying or exploiting someone, anger at being betrayed or exploited, a sense of fairness to facilitate reciprocal relationships, and an overwhelming empathic capacity.
Lack of absolute morality doesn't mean that everyone will suddenly start assaulting, stealing, or killing other people... at least not unless they are willing to expect to receive the same treatment. You get as good as you give. I think it's very telling that contemporary Christians, for example, can look through the New and Old Testaments and pick out what parts are clearly immoral, in fact lots of them are repulsed by the Old Testament, as they should be. Where's the morality in having bears maul forty two children for making fun of a guy's baldness, stoning neighbours who work on the Sabbath, condoning slavery, or ruining a good person's life just to prove to the Devil that they're faithful. There are lots of good things in the Bible, and certainly many of Jesus' teachings would be well to be followed, but they are hardly novel concepts... the Golden rule has been formulated in every language, in every society, since before hominids were recognizable; even monkeys, dogs, and other social animals have some inkling of the Golden rule. You can always pick and choose Bible passages to fit the morality of the time, and I think that the fact that we can do this suggests highly that we do not obtain our morality from the Bible. I like to think that most Christians would refuse to commit murder even if it was revealed that their God wanted them to.