In the right neighbourhood
If morality were a matter of principle, reason, or virtue, and we were capable of acting immorally, there would be natural selection for acting immorally whenever acting immorally helped us promote our genetic legacies. In other words, natural selection would trump morality if morality were non-evolutionary.
If there were selection for morality, morality would be just another way in which we could promote our genetic legacies. But morality requires that we perform actions that are biologically altruistic. Therefore, morality is neither adaptive nor an adaptation.
Boyd and Richardson point out that altruistic groups could not be invaded by non-altruists provided that the latter had a conformist bias. But the conformist bias is speculative. Moreover, non-altruists who lacked a conformist bias would be fitter than those who possessed it and the the former would eventually supplant the latter. Variation would ensure that some non-altruists lacked a conformist bias.
The only way to explain a morality that endures and that requires us to do something other than maximize our genetic legacies is to explain it as an evolutionary by-product of an adaptation from which it cannot be separated. In that case, morality could impose a cost but the adaptation would provide a benefit, and the combination would endure because the benefit would still outweigh the cost.
An evolutionary by-product theory
Here's what could work. First, we have naturally selected beliefs that we are of value. There is natural selection for them because they improve our ability to complete longer range plans when the completion is in our interests. They are not true and do not come with a rational justification.
We acknowledge others with the same belief in order to gain their cooperation on the same kind of projects. We acknowledge them as being equally valuable.
Once we acknowledge some other believers we are committed to acknowledge all others, because we have no grounds on which to distinguish the former from the latter.
Our belief switches itself off in situations in which acting in accordance with it would require us to sacrifice ourselves, our kin, or our friends.
Its evolution and confirmation
The original belief increases our viability. So does the extended belief that enables cooperation, and the acknowledgement of equality that prevents the breakdown of cooperation. The switch offs ensure that sacrifices are always voluntary and not required when they are not in our biological interest.
We can make empirical predictions that are confirmed, such as the prediction that the truly amoral should be bad at long term projects, a prediction that is borne out by the existence of psychopaths.
Moral facts
It is stipulated that acts are morally permissible when they are consistent with someone's extended belief that others are of equal value, that an act is morally obligatory when it is the only morally permissible act available, and that forbidden acts are those that are inconsistent.
Norms
The normative ethics that results is one such that we should minimize losses unless we have to sacrifice ourselves, our kin, or our friends to do so. It is a principle of minimization because the commitment is a result of our relations with others rather than a function of our possessing quanta of value.
It is also an ethics that forbids us to use others because that would amount to treating them unequally.
In sum, it is a limited consequentialism that is deontologically constrained. It is not unreasonable. It leaves plenty of room in which people can live rich lives in a variety of ways.
Moral motivation
As for moral motivation, all that is required is that if we believe something, then, if we act, we act consistently with the belief. So the default is that if we act, we act consistently with our extended belief that we and others are of equal value.
We can deviate from the default if we lack relevant true beliefs or possess relevant false beliefs. Sometimes, it is in our interest to lack true beliefs or to possess false ones, in which case we rationalize.
Ignorance, error, and rationalization result in different cultures developing different moral codes, with the result that relativism may appear to be true.
Ignorance, error, and rationalization do not change the the moral facts: actions are permissible when they are objectively consistent with the extended beliefs, not when they are merely subjectively consistent. Even a rationalizer would judge someone else in the same situation as the rationalizer to be a wrong-doer.
Moral reformers and moral saints are possible because they may have little ability to rationalize, including an inability to rationalize their society's moral code.
Meta-ethics
The theory is realist, objectivist, and cognitivist. We have moral intuitions that are like the linguistic intuitions of native speakers of Standard English about when to use the active and passive voices.
The output of the theory should not be intuitively outlandish because the theory explains our intuitions in terms of the same theoretical postulates that generate normative output, and it would be odd if they diverged. It is the only moral theory that explains why its output should be intuitively acceptable.
Our intuitions should agree when we share all relevant beliefs, and they should be correct when we possess all relevant truths and no relevant falsehoods. To do right, we must believe right.
Conclusion
The theory has a number of theoretical virtues such as simplicity and conservativism. It harmonizes ethics and biology. It puts moral facts in the right place: not so distant that their influence becomes a mystery but not so close that they become subjective. It makes us into each other's brothers and sisters.
Evolutionary intuitionism explains the origin and development of an objective, universal morality in a way that no other theory does. It explains the persistence of a recognizably human morality in a world that is existentially hostile to it.
There is a more detailed explication of the theory together with new material at Ethics for Organisms
Copyright Brian Zamulinski.