A moral prescriptive ("ought") or a moral imperative ("must") - cannot to be derived from the fact of our biological existence.
I.e, in the footsteps of Ayn Rand:
"We are not faster than the gazelle or stronger than the lion, yet by using our reason and intelligence, we can surpass them in the struggle for survival".
This conclusion, upon which she based her Social Darwinian/Nitzchean ethical system, is supposed to resolve the 'naturalistic fallacy', which states that a fact (something that "is") and a value (something that "ought" to or "must" be) are wholly distinct things and that one cannot logically derive the latter from the former.
But surely there is a glaring logical fallacy here. For her analysis to be valid, an ethical value - either a moral prescriptive ("ought") or a moral imperative ("must") - has to be derived from the fact of our biological existence. But her use of "must" in this context is not as a moral imperative, it is merely used to make a conditional statement of fact, i.e. "we must act in this way if that outcome is to be achieved, and if we don't act in that manner, then it won't be achieved".
So she has simply moved from the fact of our existence to the additional fact that our continued existence depends upon certain contingencies (from "is" to "is, so long as..."); what she has absolutely not done is move, in a logically valid way from "is" to "ought".
Yet the moral perspective as a whole IS derived from the existence of moral philosopher. It is impossible to represent moralizing lion, or a savage negotiating whether his or his progeny right to survive exists or not. It is a self-evident: "look and see it", and it would take a blind fool to argue that it is not there.
Similarly, it is self - evident that moral philosopher does NOT engage in negotiation for his own right to exist, nor for his family not to perish in a holocaust or something like that.
Continuation of moral philosophy at least within one individual is the line in the sand one cannot pass. Once the last moral philosopher dies, that's it, no more distinction of "ought" and "is" is needed to argue the case, and the only argument could be between "must" - either we must bury the body, burn it or we must eat it because we are a bit peckish.
It is never argued that Nature "ought" to exist or not. Nor any savage aboriginal has that suspicion running against his existence. Their right to exist is self-evident as we don't have any second Nature nor any other set of aboriginals to replace them in case of breakdown.
Therefore, I conclude, the moral philosopher should shut up and accept at least his own "is" being at least on par with "ought", just for the moment of pure and unembellished existence. Despite the fact that we have way too many philosophers, so we might get away with eating one or two.
Starting with one living moral philosopher as a prerequisite, we may arrive to the whole moral civilization of philosophizing individuals writing in their blogs and Facebook and questioning their own right to exist.
Which is the point where I'd like to rest my case; it is foolish to argue that it "ought" to be so, yet I am blessed for it "is" so. and it is purely my individual wish that it continues to be so and this existence won't be open to some further philosophical, yet foolish haggling.