Evolution. No deity is required.
Why Christians Must Steal From Secular Morality:
http://www.caseagainstfaith.com/submissions/steal_morality.htm
Christians must steal their moral rules from secular morality. They have no choice, as the Bible does not offer a moral system, it only offers a series of contradictory commands and a supposed threat of punishment in the "afterlife" for not following them - a punishment that is given equally to all violators - whatever the sin.
The Bible does nothing and can do nothing towards inculcating moral behavior on its own. Christians must steal from secular moral systems, and then merely graft their 'God threats' on top of this moral system. This is necessary. And the reason for this is simple: there is no morality in the Bible and there can be no morality in the Bible, because the Bible holds that 1) ALL 'sins' are equivalent (destroying any moral sense) AND 2) all moral behavior is immaterial, because works cannot save a person, AND finally all people are damned from birth.
In reality, Christians realize that some actions are more moral than others. They realize that moral actions exist in a hierarchy, and that rape is far worse than stealing a pencil. Yet the Bible holds that all 'sins' are equal, as all deserve the same punishment.
Christians also realize that humans can be moral agents... they expect moral behavior from others, and they view their own children as something to value. Yet the Bible holds that man is worthless, that he cannot be a moral agent, and that his sole salvation comes from grace. However, since Christians realize, implicitly, that all of these these points are obviously, prima facie false, they must steal from secular systems, that hold that 1) man obviously has a value 2) all 'sins' are obviously not equivalent and 3) a person cannot be held to be doing anything 'immoral' without intent.
Origin of the 10 commandments:
http://www.atheistalliance.org/outreach/news-2002_spring.php
http://www.rationalrevolution.net/articles/ten_commandments.htm
Morality Without God:
http://www.atheists.org/Atheism/cohen.html
Morals Without Gods:
http://www.secularhumanism.org/index.php?section=library&page=sharris_26_3