There is of course, no question that genes play a role in behavior throughout evolutionary history. Bees, for example are known to sacrifice their lives for the good of the hive. But while this might appear to be the result of a laudatory impulse on the part of individual bees, it is nothing of the sort. No bee decides, in a moment of supreme valor, to give her life for the good of her fellow creatures. There is no moral imperative acting here, but only the evolutionary pressure that produces an appearance of high altruism. Clearly no virus ever decides to be “good” and target the upper respiratory tract rather than the lungs. Increased transmissibility and decreased host mortality is a well known and very frequent evolutionary strategy for infectious, lethal viruses.
While these are fairly extreme examples, the same sort of thing applies to a large extent (though admittedly not entirely) to behavioral traits coded for by human (as well as other animal) genes. Increased empathy might be expected to result in behaviors that are more “morally good” according to many human cultures. But a careful examination of the literature shows this is not always the case. Genetically determined autonomic reactions to a scene of violence may lead to complex and variable behavioral outcomes. This point is made in several papers that reference the OXTR rs53576 allele of the oxytocin receptor gene, one of the most studied behavioral genes. .
Even if there were a much tighter relationship between phenotypic effects of genes related to feelings and emotions with behavioral consequences, it is very well known that both emotions and behaviors are multigenic, and often involve highly complex gene environment interactions. A large literature of identical twin studies has shown that genetics accounts for no more that 50% of almost all behavioral and mental phenotypes. All of this makes prediction of anything to do with moral actions based on genotypes of one or a few genes extremely difficult.
Taking the OXTR allele as an example of this complexity, we find that in a paper describing the effects of the gene on empathy, the A allele appears to be dominant, whereas another paper, finds the G allele to be dominant for effects on child behavior.
Both studies concur that this polymorphism is in Hardy Weinberg equilibrium, meaning that selection pressure for either allele is currently absent, and the gene probably was never a target for natural selection.
Returning to the issue of moral choices, the very fact that there is no single objective morality for all human cultures is strong evidence against an evolutionary genetic connection. Yes, there are differences in allele frequencies in many of these genes in different ethnic groups, but these differences are generally not meaningful. I was once involved in the review of a grant application which hypothesized that different frequencies of a particular polymorphism in a neurotransmitter gene could explain why African Americans are more violent than European Americans. The grant was not well received due to lack of any preliminary evidence and the implausibility of the claim. The truth is that human populations differ genetically from each other only in very small ways, and social, cultural and psychological factors far outweigh genetic factors in determining moral and ethical behaviors.
This does not mean that there are no genetic correlates with human acts of moral good or evil. All humans (except for rare variants like psychopaths) recognize the inherent good in caring for children, in love, and in doing kindness to kin and relatives. And all recognize that doing harm to these people is bad. There is no question that these moral understandings and resulting behaviors are of evolutionary origin, since the same behaviors are seen in many mammalian and even other animal species.
But we only need to think of moral values in modern cultures that extol the killing of “enemies”, the mistreatment of people with sexual or other nonconforming phenotypes, the way women are treated and so on, to see that once we go deeper than the fundamental common values, we find purely cultural determinants of morality, with no genetic influence at all.
Cultural evolution (which includes good explanations for different human moral codes) is fundamentally different than biological evolution, which depends on genetic variation. For morality it is memes, not genes that count. It is cultural evolution, not Darwinian biological evolution that has given us fire, shelter, technology, the internet and everything else that makes us more than just another ape.
Links to the papers mentioned: