Sooner or later in the discussion of theism vs atheism the issue of morality comes up.
"If you don't believe in god, what is keeping you from killing me right now?" asks the theist.
"I'm not a murderer," says the atheist.
"But if you wanted to, you could, right?" the theist pursues, cleverly trying to catch the atheist in a moral paradox. "Is your belief in god all that is keeping you from killing me?" the atheist asks.
Okay, I'll admit that that was a bit of a straw man, although that conversation has happened - and is happening - all the world over. But the point is that theists cannot imagine morality that does not originate from god, that is not pulled from the Bible, as though it were a well of pure goodness from which all of life's moral dilemmas can - and should - be resolved. And if the Bible is not the source of this morality, theists have to wonder what is.
I would consider the standard treatment of this question one of atheism's weaker arguments. The standard answer is something of a bluster about cooperative societies and suppositions about how altruism developed over time. I cringe each time I hear this used as an argument, because, while I find the subject fascinating, it does not sound terribly strong to me. It is not as strong, for example, as the argument for evolution, or the argument against the historicity of Jesus. I think that theists have played their hand well and trick most unsuspecting atheists into speaking out of turn. I think that the proper and honest answer for most people (I'll make exceptions for behavioral scientists and anthropologists and so on) is "I don't know."
I don't know. I have no idea where and when 'morality' developed. I don't think it matters, because I know that, somewhere along the line, what we call morality certainly did develop. And I don't think that just because an atheist doesn't know the answer then the theist is correct by default. Even if the theist's response (God) made sense, it would not be the de facto winner.
But the theist's response doesn't make sense. Unless I am mistaken, (possible, I suppose) the Christian's moral philosophy is summed up in the ten commandments. Thou shalt not, thou shalt not, and so on. All delivered after the Israelites have been delivered out of slavery (of which nothing is said, but is later endorsed and expounded upon) and which, presumably, the Israelites needed to be told. Including this one, which is not one of the traditional ten, but is included nevertheless. "Do not cook a young goat in a mother's milk" Really? That is so grotesque and twisted that even a non-vegetarian must be repulsed by the thought (by the way, this is where Jews get their 'no cheeseburgers' from). But there it is, followed two short verses later by the declaration that these are the ten commandments.
Okay, but what about the real ten commandments? No gods before me, no false idols (he is a jealous god after all), no taking my name in vain, remember the sabbath day... in case you were keeping count, that's commandments one through four all about praising god. So if this is the morality that theists talk about; morality that comes solely from the Bible, then they are correct. This cannot be arrived at any other way. No one would just stumble upon these specific (relatively random) rules. But how about the rest? No stealing, no disrespecting parents, no murder... did God really need to interrupt his people all this way into their journey to tell them specifically not to murder, not to lie?
It seems clear to me that however morality came to humanity, it came well before they dreamt up a god to attribute it to. Where do atheists get their morality? I don't know, but it's from the same place that theists get theirs. And without speculating where in our evolutionary history we developed this morality, it makes perfect sense that we did. Without morality we would have been unable to create society where we can protect each other and grow together. Without this basic morality (which changes from culture to culture and from decade to decade) we would not have built pyramids or churches, developed art or poetry, braved the waves or gone to the moon. It is clear that humans are at the top of the food chain, and one of those reasons is that we were able to band together in cooperative societies and fend off wolves and hyenas and lions and, at the same time, develop language and art and the rudiments of civilization. How we developed is extremely interesting, but is not at all relevant to the discussion of god. The Bible is replete with bad advice and evil plans. Whoever follows such a jealous and bigoted god is not thinking clearly.