Reproductive sustainability is an "is" - something aids or harms reproductively sustainability. But you still need to subjectively decide that it's something we "ought to" be striving towards.

We may have an evolutionary drive to (roughly) strive towards reproductive sustainability, but we still need to decide whether we "ought to" listen to that drive.

Also, this is going to sound pedantic, but it's going somewhere.

So you said "a society in which murder is universally practiced would be reproductively unsustainable":

• What does "universally" mean? Murder is just a single action. If every person tried to murder at least one other person, you could probably still have a reproductively sustainable society (subject to some guidelines and/or a sufficient birth rate).

  Maybe you mean it's practiced constantly or frequently, by everyone. But, depending on the threshold, one may find that eating certain foods or doing certain recreational activities too often may be sufficiently risky or harmful to one's health, to make it reproductively unsustainable if everyone practiced that.

  If one takes it to the extreme and consider doing nothing but that, then absolutely nothing is reproductively sustainable. Even doing nothing other than reproducing all day would be unsustainable because you'd die of thirst or exhaustion.

• Not everyone wants to murder, so why consider a hypothetical of it being practiced by people who probably wouldn't practice it, if given the option. It would make more sense to only consider it being practiced by those who want to do so. That's much more likely to be reproductively sustainable.

  If we compare that to celibacy: if everyone practiced celibacy, that would be reproductively unsustainable, so should that be illegal? I would say no: it would be a slippery slope fallacy to say that some portion of the population shouldn't be allowed to do something because everyone can't do it. It's illogical because many people do want children.

Basically, this would be a poor basis for morality. It would include a whole range of things that doesn't harm anyone, and which can be practiced by everyone who wants to, without leading to reproductive unsustainability.

A much better basis for morality would be well-being.

No.

You would just be displacing the "ought" into the unstated premise: "we (as a species) ought to be sustained."

That premise requires justification.

Nature tells us nothing of what ought to be; it only tells us what is.

To the naturalist, this is a hard pill to swallow. Because they base their entire worldview on a scientific mindset, it is difficult to accept that the concept of "ought" is not a scientific question, but a fundamentally ethical one.

This suggests that Evolutionary Psychology may simply be a way to frame complex social and psychological concepts through "the lens of the monkey"—essentially providing social theories with a veneer of scientific backing and credence they might not otherwise possess.

Ultimately, this highlights the tension between a completely Overlapping Magisteria and the Non-Overlapping Magisteria (NOMA) theorized by Stephen Jay Gould. Do you believe that ethical or "religious" questions can be explained by non-philosophical professions, or do you maintain the independence of these Magisteria? Or, perhaps, do you hold to a middle ground where these fields influence one another while remaining methodologically independent?

Well.. I think that naturalistic grounding for morality isn't about 'murder' or 'non-murder'— it’s about the survival of the group.

Individual actions are just tools. Historically, Homo sapiens competed with Neanderthals and rival tribes.. If your tribe refused to use violence while the other practiced it, your tribe disappeared. As a result, there is no one left to be 'moral' if they don't first survive the 'is' of biological competition.

In this sense, 'Ought' is a luxury of the 'Is.'

When your 'Is' includes a full fridge and a police force, your 'Ought' becomes 'Be kind to everyone.' But when the 'Is' is starvation and war, the 'Ought' becomes 'Kill or be killed.' For example.. Extreme cases like death camps: people share their last bread not because of a 'higher' cosmic truth, but because we are biological machines running a group-survival program. We are evolved to prioritize the gene pool/tribe over the individual 'self.'

So.. The 'Is-Ought gap' doesn't need a bridge, it needs a reality check.

I think that you can indeed derive morality from natural evolution — but inversely.

Evolution, ultimately, means survival of the fittest. The weak is the prey of the strongk. Species rise and go extinct. The destiny of life on Earth was always to end when the Sun becomes a red giant and eventually engulfs the planet. Mothers care about their pups. The pack cares about its members. Everything else is sacrificable. The more adapted you are, the more you will rise, without impediment. The less adapted you are, or if you are unlucky, the more you will fall, with nobody offering you a hand. Everybody is a slave to their environment, their genetics, their biology, and you have to cope with that at the best of your abilities.

If there is one thing that makes humans special (I am not sure, but if there is, it is this), it is that we can rebel against the above slaughterhouse.

We can say to nature and to evolution: “We will not accept your mechanisms and rules. I will forge my own rules. I will learn to fly, to reach the sky. I will save the weak and restrain the strong. I will cure the ill, and genetic luck will not determine if you will surive or not. I will defeat pain, predation, and suffering — the endless carnage — and I will achieve immortality and eternity. I will learn to control my egoism; I will try to be empathetic and caring not only toward my own babies and my tribe, but toward all of humanity and all living beings. I will not simply be on Earth to survive, to win the evolutionary race and reign over nature, but to become its guardian and protector. I will deflect asteroids, and I will create beauty, knowledge, and understanding.”

That is what a higher morality would aim to look like. Are we able to do it? Most of the times, no. But we can conceive it, and try... and to some degree, we have done a lot.

So, I see morality as something deeply and radically anti-evolutionary. You can argue "but this is part of evolution itself!", to which I reply: ok in this case, morality is derived this last evolutionary step, breaking the chains of patterns and rules from previous phases. This does not mean hating Nature or renouncing our belonging to it. It means refusing to be a necessary slave to nature and its mechanisms, and claiming the freedom to do and be otherwise, as individuals and as a species (and perhaps as an entire ecosystem, when and if we will be ready for that)

Is this a delusion of omnipotence on the part of those who think they can defy the laws of the universe and effectively make themselves gods? Is this pride? Yes, it may be. Probably it will be the cause of our downfall. But I'm grateful for this pride.

Background assumption: there are distinct moral beliefs, "generated" by a specific "moral belief generator" or by the same generator as any other beliefs.

Now, you might be thinking that if we could show that specific moral beliefs are implanted in us, in our genetics, in the course of evolution, that would be (at least part of) a bridge between "is" and "ought." This would not seem so feasible if we emphasized a very abstracted concept of "ought" (or "good" or whatever along this line), but might be more defensible modulo the concept of thick ethical concepts (SEP), ones which (allegedly) can't be "neatly" broken up into a normative and a non-normative component.

Waiving that, though, evolution would seem to "act on" not individual beliefs, but whatever the generator for moral beliefs (or subdoxastic concepts) is taken to be. Otherwise we would face a version of Plantinga's pseudo-evolutionary argument against naturalism (that if our beliefs are not intrinsically truth-oriented but merely "evolved as beneficial to survival strategies," we would somehow not have sufficient reason to trust our beliefs; the rejoinder is that the belief-forming mechanism, when it evolves, evolves as truth-oriented in general, and individual beliefs are not (or not usually) individually evolved; I'm not born believing for or against e.g. the Continuum Hypothesis, or the immorality of genocide, or the curvature of the Earth).

But perhaps we could retrace our steps some, and consider whether, "Murder is wrong," is really so specific. Maybe it's like, "1 + 1 = 2," a bit particular, but also a bit general, and so perhaps more plausibly traceable to evolution in that respect. The SEP entry on the determinable/determinate relation indicates that perfect particularity might not always be attainable, in which case it could be dialectically unfair to push the meta-belief that various "common sense" moral beliefs are too particular to have evolved in us.

This is really an argument using teleology to derive an ought from an is. It is similar to the statement that one "ought" not to sacrifice one's queen during the first few moves of a game of Chess, which attempts to bridge the is-ought gap by assuming that the goal of playing Chess is to win.

Here, the teleological assumption is that biological life has a purpose, and that purpose is to reproduce. Once you accept that, it follows that one ought not to do things which are reproductively unsustainable. It's not hard to imagine that actions such as murder could fall into that category by undermining social cohesion.

It is a case of seeing repeated behaviour (of microbes, plants and jellyfish, reproducing) and inferring that the behaviour must have a goal. It is not so different from Paley seeing complexity and inferring that there must be design. But one can release a ball from a balcony and every time it will fall towards the ground, yet that does not mean that the purpose of balls is to fall downward.

Effectively, it is trying to derive morality from a command to "Go forth and be fruitful", and saying that the command comes not from a Middle Eastern deity but from something called "nature" or "evolution". Either way it's still possible to consider that it's a command which has not been fully justified or lacks authority. Many people think nature is mindless and has no intention, but some people might think nature is actually evil and should be disobeyed.

At best, this gives us a naturalistic justification for human societies to label murder as wrong, something to be discouraged and sanctioned. Maybe hunter-gatherer groups which did not consider murder blame-worthy tended to go extinct? But you can't derive rightness or wrongness from survivor bias. After all, naturalistically speaking there is no right or wrong when species fail to reproduce or go extinct, it has been very common as long as there has been life on Earth.