The subject of how atheists can be moral without an absolute morality handed down from the gods has risen its ignorant head again, and frankly I am tired of this insulting nonsense. Not only should the personal benefits of behaving in a basic moral fashion (no stealing, murdering, etc.) be obvious, but a sense of reciprocity has been evidenced in apes. Its a part of our wiring. Hell even robots with EAs develop cooperative behavior (see the blinking food-seeking poison-avoiding robots featured on sciblogs on a link I can't find at the moment).
Wherever morals originate in a philosophical sense, they only sustain themselves in a population if the people practicing them produce more people doing the same, either by birth, or persuasion, or killing those who disagree. There's a good reason there's never been a major religion that said "go forth and be sterile", and it didn't have dick to do with what any gods had to say about it. Ask the Shakers.
We follow the moral rules we do for the same reasons you have ghost runners and no hitting to the opposite field when playing baseball with limited players: it works. I mean really, what sort of person needs a god to tell them that being a theif isn't something one ought to do? All you good Christians who can't understand how we atheists behave morally without believing in an absolute morality from an absolute source are cordially invited to try to live like you say we should (inferentially) for a while. Lie, cheat, and steal whenever you think you can do it to your benefit and get away with it. See what happens. Please. Pretty please, with sugar on it. Just don't say I didn't warn you.
You'll learn what we already reasoned out - it sucks. Better to be honest and expect others to be honest. Get a lot more done that way. And its nice to not be looking over your shoulder all the time. Sleep better that way. No gods needed. It works. Period. So really, if you need your gods to resist your impulses to toss babies into woodchippers, I'm glad you've got them. Just don't insult my intelligence implying you are somehow morally superior to me because I can resist doing so without one.