In an earlier post I questioned the existence of atheist essentialist philosophers. I had been looking in the area of Philosophy of Science. Turns out a better place to look is Moral Philosophy. Moral Philosophy presents a moral spectrum, from Moral Nihilism (nothing is moral or immoral), to Moral Relativism (morals are relative to individual, social, cultural, or historic circumstances), to Moral Universalism (applies to "all similarly situated individuals") to Moral Realism (moral statements can be objectively true, and subject to rules of logic). In Moral Realism moral rules are similar to Platonic Forms or Ideals. Moral Realism is often grounded in religion, but is also supported by some atheist philosophers (example: Quentin Smith).
The boundaries between the positions are often fuzzy, with various proponents subtly repositioning other prominent philosophers. A historical stumbling block has been determining how a Universal Morality can be possible without recourse to a deity (and this is the basis of the "argument from morality", a proof of God's existence). More recently, based on research in Evolutionary Psychology, Steven Pinker wrote a great essay on how a human moral sense or instinct may have evolved. He presents many rules which are specific to the evolved nature of humans, and some which may be more universal. He says:
"Two features of reality point any rational, self-preserving social agent in a moral direction. And they could provide a benchmark for determining when the judgments of our moral sense are aligned with morality itself... One is the prevalence of nonzero-sum games. In many arenas of life, two parties are objectively better off if they both act in a nonselfish way than if each of them acts selfishly... The other external support for morality is a feature of rationality itself: that it cannot depend on the egocentric vantage point of the reasoner..."
It is interesting to consider how many rules the Moral Realist propose are universal, versus specific to the evolved nature of humans. I wonder how much science fiction Moral Realists read. A common theme in science fiction is the presentation of different alien races, and the different moral imperatives which naturally arise from their different evolutionary heritage. Examples are the K'kree (herbivores) and Hivers (one sex) from Traveller. And aside from other planets, we can similarly consider how morals would differ if radically different earth species (sharks? praying mantis? naked mole rats?) had evolved sentience. The Moral Realists imply that all creatures, regardless of evolutionary heritage, will always converge on the same universal morality (or that creatures which are unable to meet the standard can't achieve sentience). This may be a realistic assumption for a few of the meta-universals proposed by Pinker, but I don't think it applies to the much larger set of rules proposed by the Moral Realists. And without this universality the attempt to use rules of logic falls apart.