I think you missed the point
I am not arguing that I really know which came first, ethical principles or religion. I am saying that your blanket statement that ethical principles were originally codified in religion is a claim which I don't think you have real support for. (FWIW I suspect that the answer to which came first may depend in the end on how broadly you define each of religion and ethics. Certainly if you define ethics broadly enough, you can find good evidence of ethical motivations in, for instance, chimpanzees.)
First of all it is true that the earliest philosophical writings we have are predated by religion. I agree with that, and were it otherwise I would be saying something rather different.
Secondly it is both true that in every human society we find both some sort of shared ethical system and religion. Given that, your comment about the distribution of religious artifacts is not evidence one way or another on which came first. It is an argument that religion is a universal tendancy. It doesn't indicate whether that universal tendancy predated the one to shared ethical systems.
Cheers,
Ben
PS You may be asking why I care. It is simple. I am just tired of religious people telling atheists like myself that our morals come from religion, one way or another. They certainly don't directly, and I am not convinced they do ultimately either.