Elsewhere, Nietzsche, setting aside the physiological aspect of the body, attributes a purely social origin to morality: Wherever we encounter a morality, we also encounter valuations and an order of rank of human impulses and actions. These valuations and orders of rank are always expressions of the needs of a community and herd: whatever benefits it most—and second most, and third most—that is also considered the first standard for the value of all individuals. Morality trains the individual to be a function of the herd and to ascribe value to himself only as a function. The conditions for the preservation of different communities were very different; hence there were very different moralities. […] Morality is herd instinct in the individual ¹.

Here, Nietzsche no longer interprets morality through the lens of physiology. The 'herd instinct' is a social instinct, not specific to each individual's physical constitution. It is not because I am weak that I embrace a particular moral code, but rather because society has chosen it, and, as a member of that society, I adopt it too.

Finally, Nietzsche traces the origin of Christian morality to a psychological state: ressentiment (which he defines as a kind of bitter anger arising from one's own sense of weakness and jealous envy of those who are not): The slave revolt in morality begins when the ressentiment itself becomes creative and gives birth to values: the ressentiment of those beings who are prevented from a genuine reaction, that is, something active, and who compensate for that with a merely imaginary vengeance ². Ressentiment drives the weak to create morality, condemning the freedom and self-assertion of the powerful, and thus becomes the origin of morality.

These three origins are indeed interconnected: psychological ressentiment stems from the physiological weakness of the body, and equally, I accept society's moral norms because my physical limitations make it difficult to break free from the herd. The concept unifying these three approaches—and ultimately constituting the true origin of morality—is self-interest.

I adopt a moral code because it aligns with my self-interest. If I am humble, it is because, as a weak person, it serves me well not to be arrogant, helping me avoid provoking the powerful: When stepped on, a worm doubles up. That is clever. In that way, he lessens the probability of being stepped on again. In the language of morality: humility ³.

It is in my interest to be moral both on account of my physiological weakness and to avoid society's punishment for immorality. Ressentiment reveals that I act morally out of self-interest, not from any genuine appreciation of morality; my envy of the powerful betrays a desire to be amoral, as they are.

c/ Criticism of Nietzschean Genealogy

Through Nietzsche, we may have identified the origin of morality—and, by extension, of religion: self-interest. It is in my interest to be moral and for there to be a God. This much we can grant Nietzsche. But he goes further than merely affirming this origin; he elevates it to the status of a foundation. In other words, the origin of morality also becomes its foundation (by 'foundation', I mean, according to two possible interpretations, either its truth or its value).

Let us examine precisely how Nietzsche moves from the origin to the foundation of morality.

Nietzsche begins by acknowledging that he does indeed distinguish between these two questions: Basically even then the real concern for me at heart was something much more important than coming up with hypotheses about the origin of morality [...]. For me the issue was the value of morality—and in that matter I had to take issue almost alone with my great teacher Schopenhauer ⁴.

He thus asserts that grasping the origin of morality is only secondary to a far more ambitious project: grasping its value—or its foundation. Indeed, he argues that even if the origin of morality were rooted in error (for instance, a people's mistaken opinion about their own morality), this would not necessarily diminish its value: But the worth of a precept, "Thou shalt," is fundamentally different from and independent of such opinions about it, and must be distinguished from the weeds of error with which it has perhaps been overgrown: just as the worth of a medicine to a sick person is altogether independent of the question whether he has a scientific opinion about medicine, or merely thinks about it as an old wife would do. A morality could even have grown out of an error: but with this knowledge the problem of its worth would not even be touched ⁵.

As we read further, it becomes clear that Nietzsche never actually addresses the question of morality's foundation, focusing solely on its origin. His condemnation of morality thus rests entirely on uncovering that origin, following an implicit line of reasoning—remarkable, given that it underpins his entire critique of morality—which may be summarised as follows: morality originates in self-interest, a contemptible quality with negative value; therefore, morality itself is contemptible and without value.
Straightforward as this reasoning may appear, it is in fact a problematic conflation, and one we find unacceptable for several reasons.

1. Ibid., §116
2. On the Genealogy of Morals, chap. 1, §10
3. Twilight of the Idols, Maxims and Arrows, 31
4. On the Genealogy of Morals, Prologue, §5
5. The Gay Science, §345