Thanks for your reply, @Bob.
What I’m calling ‘functional morality’ is the meta-ethical idea that morality is the product of an evolved instinct in humans, rather than a fact the exists outside of humans to be discovered in the world. It is secular by supposition, and realist and pluralist as a consequence.
It’s realist because there is a ground truth: evolutionary fitness. It inherits all the uncertainty of that concept, but it is nonetheless a ground truth.
It is pluralist because the specific moral systems that flow from the instinct vary. The instinct is for 1) certain basic subjective moral sentiments like ‘good’ and ‘bad’, and 2) a developmental scaffolding that leads those sentiments to be attached to certain social behaviors. The specific behaviors differ by the specific constraints of the group, as well as by the random walk of cultural evolution; the developmental scaffolding only causes the group to settle on a set of norms and expectations about how to behave.
Because it is evolved, it necessarily exists or existed, in at least a rudimentary form, in non-human animals – for example, the pre-human animals that evolved into humans. It doesn’t exist in all animals, and it doesn’t mean that animals that have it will have a morality that includes humans as moral patients. But we can see rudimentary morality in social animals, particularly our close animal relatives. Behaviors that suggest animal morality include: reacting angrily when they are paid less for the same task; refusing to electrically shock another animal to get food for themselves; risking their lives to save a pack mate – or even an animal of a different species.
We might say these behaviors aren’t ‘moral’, because they are somehow self-interested, but human morality too is often self-interested, as when doing the right thing avoids punishment or social repercussions. If we say that nothing that animals do is moral, we would also need to exclude many human behaviors that are usually understood to be moral.
If human morality looks more complex, it’s because the human ability to abstract – and to believe in abstractions – is significantly greater than in animals. As we can feel pain when our favorite sports team loses, so too can we associate moral sentiments with symbols and myths.
And this goes in the other direction as well: you mention single-cell organisms, and I don’t think there’s a problem with identifying something in common between the reciprocal behavior of those organisms and the more complex reciprocal behavior we call morality. Cooperation is often a good evolutionary, and morality is just one of those strategies. Where little more than chemical reactions are enough to trigger cooperation at the level of single cells, in more complex life we see more complex behaviors, and in its most complex form in humans we see group consensus building around abstract moral principles.
But the principles should be constrained by the meta-ethics.
To take an analogy, pleasure and pain are also evolved instincts that increase fitness: calorie-rich foods and sex are pleasurable; physical damage and social rejection are painful. But because we can understand this, we can also understand that, though surgery hurts, we shouldn’t avoid it; and though drugs feel pleasurable, we shouldn’t overindulge in them.
The argument I’m making here is that a moral principle like antinatalism is similarly a mistake. Though it feels like it’s ‘good’ because of the complex social and cultural abstractions that justify it, it undermines the pursuit of evolutionary fitness on which the very concept of the good is based. Reproduction must be a moral good at the margin, because that’s where the rubber meets the road in evolution.