Why be good?

[Ben Davis]

What I am asking is: what is the BASIS for objective moral behavior? Where does it come from?

Firstly, there is none. 'Objective' moral behaviour doesn't exist. All morality is subjective. So if we correct your question to 'What is the basis for moral behaviour?', you've already been given the answer. I'll repeat & simplify:

The basis for all moral behaviour, like everything else in our evolutionary development, is survival. Humans developed as a social species because those who behaved socially survived and reproduced more effectively thus propagating the genes for social behaviour. Further along human development, those societies which developed ethical standards (commonly referred to as social contracts, the precursors of law) survived better because they increased the effectiveness of social behaviour.

That's the basis, that's where morality comes from, all of it. No gods required.