Research in anthropology and related disciplines reveals that there is no strong evidence of any universal morals; there are no set of moral beliefs that are found uniformly across all existing countries or cultures. This has often been interpreted to mean that morality is unrelated to the existence of a deity. Some, however, believe that while the lack of universal morals is true it does seem that there is a universal sense of “oughtness”, or a universal tendency to justify what we do, or to place value judgments like “right” and “wrong” on behavior. From a philosophical perspective is this universal tendency toward morality better explained by a need to “get along” to increase fitness in our world (roughly a sociobiological explanation of morality), or is it perhaps better explained by our possessing an intrinsically moral nature, i.e. one that may exist because of the existence of a deity or deities (or even because life may continue after physical death without the existence of a deity). Sociobiology, if true, surely can provide sufficient grounds for the existence of morals; but I wonder whether this is a plausible and coherent explanation (e.g. where, for example, does the force or authority of morals come from?).

About universal morality: while it's true that among cultures (as among individuals within any culture) there are variation in moral beliefs (as well as scientific beliefs), there are general (nearly universal, so far as I can tell) moral categories. One finds incest regulations, for example, in every society (though the boundaries of those prohibitions vary). Rules concerning possession, killing, and even, arguably, the sacred are more or less universal. I would be pretty reluctant to walk into any human society and start taking bites out of people's children. Moral beliefs and conduct do exhibit variation, but variation by itself doesn't disprove the existence of universal commonalities. Any pharmacist will tell you that different people respond to different drugs differently, but that doesn't refute the universal laws of chemistry.

Human moral life, then, exhibits both remarkable variation and remarkable commonality. As you say, there are various possible explanations for this. Philosophically, however, I think more naturalistic explanations (biological, sociological, etc.) preferable simply because they depend upon empirical and conceptual matters in a way that's likely to produce more agreement than religious explanations. Note that the existence of moral universals would not prove the existence of a deity any more than the existence of moral variation disprove deities' existence. And that's just the problem with matters divine. The deity's existence or non-existence is consistent with any empirical data. So far as human explanations go, then, it's better to stick to those for which conclusions can be reached on the basis of more or less objectively determinable observations and reasons.

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