Why Is Is Not Ought / Evolutionary Biology

The cleanest gap in philosophy

Hume noticed it in a single paragraph: writers reason along about what is and what is not, and then, imperceptibly, slip into what ought and ought not to be. The substitution happens so smoothly that we rarely catch it. But it is a leap, not a step. No pile of facts about how things are contains, hidden inside it, a conclusion about how they should be.

This is the hinge of the entire topic. Everything in the preceding essays is an is. We are evolved, not designed. Our minds chase fitness, not truth. Our drives serve replication, not us. Our instincts are tuned to a vanished world. All true, all factual — and none of it, on its own, tells us a single thing about what is worth doing.

The naturalistic temptation

The temptation is everywhere, and it is seductive precisely because evolution explains so much. Having learned why a drive exists, we slide toward treating that explanation as a justification.

It runs like this: this impulse is natural, therefore it is good. Aggression is natural, so it must be permitted. Hierarchy is ancient, so it must be right. This craving is deep in our biology, so honour it. Each inference feels grounded — it is standing on real science — and each is invalid. “Natural” is a claim about origin. “Good” is a claim about value. The first never entails the second. To say otherwise is to commit what Moore called the naturalistic fallacy: reading a value straight off a fact.

Nature is not a normative authority

The reason the inference fails is that evolution is not a moral authority, and was never trying to be. It is a blind statistical process that maximized one quantity — replication — with utter indifference to suffering, fairness, dignity, or truth.

If “natural” meant “good,” then infanticide, infection, the parasite that eats its host alive, and the casual cruelty of every food chain would all be good, because all are thoroughly natural. We do not accept that, and we are right not to. The moment we judge any natural fact as bad — disease, say — we are applying a standard of value that nature did not supply. The standard is coming from somewhere else.

Evolution gave us the capacity to value. It did not, and could not, tell us what to value. Those are different gifts, and only the first came from biology.

The gap is a door

It is natural to feel the is–ought gap as a loss — as though biology promised to ground our values and then failed to deliver. But the gap is not a failure. It is the precise location of human freedom.

If facts about our nature did dictate our values, there would be nothing to deliberate. We would simply read our obligations off our wiring, like any other animal. The gap is what makes valuing a task rather than a reflex. It is the space in which a person can look at an inherited drive and ask, not “how strong is this?” but “is it worth obeying?” — and sometimes answer no.

That space cannot be filled by more biology. No further fact about genes or instincts will ever cross the line from is to ought, because the line is not made of facts.

Where this leaves us

So the science of human nature does indispensable work and then stops at a wall it cannot climb. It tells us, with growing precision, what we are, where our wants came from, and which of our intuitions to distrust. It clears the ground of illusions. And then it hands us, unanswered, the question it was never equipped to address:

If our origins do not supply our values — if nothing we are tells us what we should want — then where does value come from at all, and how could anything genuinely matter?

That question is no longer biology. It is the beginning of the next inquiry.