I have heard many smart people talk about this and it seems to be a place that the theists among us have a strong case.  Does our (humans) idea of right and wrong come from a god or gods and if not where does it come from?

I am just going to state my case and then talk about where it comes from.  My case starts from a question or maybe several questions.  Why are humans so successful on this planet?  Are they the strongest animal on the planet?  Are they the fastest animal on the planet?  I would say that if you place a naked human in a cage with any hungry large predator on the planet (tigers, lions, bears, etc) the human will be a meal for the predator.  This being the case how is it that these large predators don’t just make meals of humans and we have nothing to say about it?

I think that the power of the human species is in our groups and in our cooperation.  We can conquer anything together.  When it is a tiger versus our tribe and our technology then the tiger dies.  I want to repeat that, our strength and success on this planet is because we help each other.  Said in another way, when humans work together it increases the reproductive success of everyone in the group, therefore we all benifit from cooperation.

What are morals?  We might say they are  rules about humans not harming other humans.

What is the reason that we should not harm other humans?  The theists say that it is because god or gods said so.

I say that anything that a member within the group does that causes instability in the group harms the group.

If you kill someone in the group then we must protect the group from you, so we must find out if there is a good reason for why you committed murder.

If you steal someone’s property and this type of action was allowed to continue then people would not have a reason to work for themselves and improve their own personal circumstance so the thief is in essence causes group instability.

If you cuckold a member of the group you are bringing about group instability by hurting the stability of a relationship which could lead to violence and murder.

Do unto others as you would have them do unto you is a good way to say that the stability of the group is paramount for the survival of everyone.

What is happening today is that our group is becoming all of the people in the human race so we can no longer attack the people in our out group because our in group is being redefined as the human population of the planet.

I hope this is a starting point for more thinking but in the mean time think about it.