Evolution of Morality

Insecure Christians are fond of claiming that their religion is important because people would be immoral without it. For example,

If we just evolved the idea of morals is flat out stupid - Obviously if I kill my neighbor and take his job and wife I am doing a better at providing for my survival and that is the theory of evolution - this happens all the time in nature - Moral ideas without God is just an opinion nothing more.

But that isn't how evolution works. Evolution is about populations.

Imagine two communities, one where people are immoral, killing their neighbors and taking their wives, and another where people are moral, refraining from murder and promiscuity. The immoral community will spend a lot of energy on internal turmoil, they will lose productivity as people are murdered, the males will be less interested in taking care of children not their own.

Meanwhile in the moral community people are happy and productive. People can generally rely on individuals to stick around and not be murdered, so they can plan for future growth of their community. The males know which children are theirs, and so have a large stake in their care.

It's pretty clear that after only a few generations, the moral community will be much larger than the immoral one. It doesn't matter that immorality can often benefit a person at the expense of others. What matters is which population grows the fastest.