Moral naturalism in modern moral philosophy proposes there are “natural facts” of one sort or another that provide an objective basis for what is and is not moral. Relevant science of the last 45 years or so supports the existence of such facts. However, I have never seen such natural facts specifically called out. Below is my proposed list of five. They provide a basis for morality that I find appealing. Comments are welcome.

In the following, “benefits of cooperation” are shared goals achieved by cooperation. “Indirect reciprocity” advocates punishment of “free-riders” along with cooperation with others regardless of whether they are expected to directly reciprocate. Additional explanatory information is in parentheses.

1) In our physical reality, benefits of cooperation are commonly available, and they can be particularly large for intelligent species.

2) However, initiating cooperation exposes one to exploitation by “free-riders”, those who accept help but refuse to provide help to others. (Exploitation of others is always a winning strategy in the short term and sometimes can be in the long term. Exploitation destroys motivation for cooperation and thus opportunities to obtain the benefits of cooperation.)

3) The above circumstances create the cross species universal cooperation/exploitation dilemma: how to sustainably obtain benefits of cooperation without being exploited.

4) Cooperation strategies such as “indirect reciprocity” solve this universal cooperation/exploitation dilemma and are encoded in our moral sense and cultural moral norms. (The benefits of cooperation made possible by indirect reciprocity are the selection force for elements of indirect reciprocity encoded in our biology and cultural norms. For example, the emotions empathy and loyalty motivate initiating indirect reciprocity. But for indirect reciprocity to be maintained, exploiters must be punished. Thus we must expect that violators of these elements of indirect reciprocity, whether encoded into our biology or in cultural norms, will be commonly thought to deserve punishment. Cultural norms and judgments whose violation are commonly thought to deserve punishment are called moral norms and moral judgments in all cultures. This is the way science grounds the human moral sense and cultural moral codes in natural facts.)

5) Strategies such as indirect reciprocity that overcome our universe’s innate cooperation/exploitation dilemma without exploiting others are universally moral, both empirically among people and theoretically for all intelligent beings.

Consider “Do not kill, steal, or lie”. These are norms whose violations are commonly thought to deserve punishment. These admonitions are heuristics (usually reliable, but fallible, rules of thumb) for elements of indirect reciprocity. Each of us is admonished to not do these things to other people, even when we really want to, and they are expected to reciprocate and not do them to us.

Perhaps the most powerful known heuristic for indirect reciprocity is “Do to others as you would have them do to you”. Jesus is quoted as saying it summarizes morality. Science now tells us why it does.

The morality of applying the Golden Rule has been rightly criticized for certain circumstances, such as when dealing with criminals and in time of war or simply “when tastes differ”. Understanding the Golden Rule is a heuristic for indirect reciprocity clears up a lot of confusion. First, the Golden Rule advocates initiating a cooperation strategy. If you are not seeking to cooperate in some sense with a criminal or an enemy in time of war, it would make no sense to apply it. Second, when “tastes differ” and you know others would not like done to them what you would like done to you, then strictly following it would initiate conflict, not cooperation. Finally, the Golden Rule is not a moral principle. It is an incredibly useful, but fallible, heuristic for choosing moral behavior.

But what about moral norms that exploit out-groups such as “Women must be submissive to men” and “Homosexuality is evil!” or are markers defining favored in-groups such as “Cutting your hair disrespects God” or “Eating pigs is an abomination!”? Empirically, these moral norms are not universally considered moral. Theoretically, they are not universally moral to the extent they exploit out-groups. If we prefer morality that is universal, then we can cheerfully reject all of these norms as either immoral or morally irrelevant.

Like the rest of science, 1) to 5) are all ‘is’ claims. How do we know they are the basis for what morality ‘ought’ to be? We don’t. Science tells us nothing about what we imperatively ‘ought’ to do or what our goals ought to be. Moral philosophers remain fully free to continue pursuing perhaps unanswerable questions about what morality ‘ought’ to be. This science about morality is useful for the following reasons. It reveals strategies for achieving commonly shared goals such as increased well-being, saving the environment, and many other goals through increased cooperation. Also, since these strategies are what largely shaped our moral sense and codes, following their imp0lied morality will be uniquely motivating. Finally, since these strategies solve the cross-species universal cooperation/exploitation dilemma, they can be expected to be recognized as moral ‘means’ by all sufficiently advanced intelligent beings and that universality is, in itself, attractive.

The moral binding power of this science comes from un-mysterious sources: the social force of cultures that advocate and enforce such a morality, the motivating power of our individual moral sense, and the intellectual charm of a universal, internally coherent morality.

Cultures need moral codes in order to survive and prosper. On the one hand we can choose moral codes based on the morality that is innate to our universe. On the other hand, we can define our morality based on theism, whatever our cultural morality happens to be, or on perhaps unanswerable philosophical questions such as “What is good?”, “How should I live?” and “What are my obligations?”. Or since this science based morality makes no claim to define what we imperatively ‘ought’ to do, is the implication that we can choose only one of these possibilities a false choice?

Perhaps at least theists and philosophers asking the above questions (which are both interesting and important) could improve the coherence and usefulness of their work by integrating in what science tells us morality ‘is’: solutions to the universal cooperation/exploitation dilemma. Theists might even describe this science as the morality encoded into our physical universe by a benevolent god and thus available to all intelligent beings from the beginning of time to the end of time.