A good amount of ink has been spilled in evolutionary biology circles over how to understand human morality. (Note: this is by nature a very different enquiry than those pursued in philosophical metaethics)
I’m convinced that what distinguishes human morality from other animal behavior (such as the concern for conspecifics shown by primates) is our ability to reason about our emotional reactions to ‘moral’ situations.
Increasing amounts of research are showing that moral judgments are not much more than emotional responses to certain specific cases. For instance, we recoil with disgust and decisiveness at the possibility of tossing an individual into a harmful scenario in order to save the lives of others (Greene, J et al., “An fMRI Investigation of Emotional Engagement in Moral Judgment,” 2001). Likewise, research on patients with damage to regions responsible for controlling these emotions exhibit near universal tendencies to pass judgments based on a utilitarian calculus (Koenigs, M et al., “Damage to the prefrontal cortex increases utilitarian moral judgments,” 2007). There is good reason to believe that a similar process is responsible for decision making in rats and other animals (Rice, GE and Gainer, P. “Altruism in the albino rat,” 1962). If it’s the case that our moral decision making shares its emotional basis with other animal behavior, then we must face two possible conclusions: 1) human moral decision making is identical to animal decision making, the upshot of which is that human moral decision making is no different than other sorts of human decision making; 2) there is a unique human characteristic that differentiates human moral decision making from other animal decision making and perhaps from other types of human decision making. The second conclusion is much more plausible, in my view.
So what is this unique human characteristic? It strikes me as somewhat obvious that this couldn’t be anything but our ability to reason about our own decisions, even though those decisions were undubitably driven by our emotional leanings. In other words, we differ from other animals in that we can think about our emotional responses and, perhaps, adjust or fine tune future emotional responses through the process of reasoning. Perhaps we can even reason ourself beyond emotion-based decision making; individuals who have spent sufficient amounts of time reasoning about moral decisions could hone their moral responses into accordance with a set of rational principles they have adopted.
Jonathan Haidt may be right that morality is a posthoc reasoning about how we respond innately or intuitively (Haidt J, “The emotional dog and its rational tail,” 2001). And perhaps this is precisely what makes our moral sense unique. At any rate, this gives us good reason to preserve our deliberation over normative ethics. Although, I would argue, I think the growing body of empirical evidence suggests that the relevance of speculative metaethical discourse is waning.