Elsewhere, Nietzsche, without any physiological consideration as to the notion of body, attributes to morals a purely social origin: 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.

In this case, we can see that Physiology no longer is the perspective adopted by Nietzsche: the ‘herd instinct’ does not deal with the body, specific to each individual, but consists in a purely social instinct. I choose such and such morality, not because I am weak, but because the society in which I live has made this choice, and that, as a member of this society, I adopt it too.

At last, Nietzsche attributes the origin of the Christian morality to a psychological feeling: the “ressentiment” (which could be defined as the angry consciousness of our weakness, and jealousy about strong people): 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. The resentment leads the weak to become moral, in other words to blame the freedom and the self-affirmation of the strong: so this feeling is origin of morality.

In fact, these three origins are obviously related to each other: psychological resentment comes from the physiological weakness of our body, and we adopt the morality of society, in which we live, simply because we are so weak that we cannot dissociated from the herd. The notion which connects these three approaches, and finally embodies the authentic origin of morality, is that of self-interest.

If I adopt this or that morality, it is because it is in my interest to do so. If I am humble, it is because I have an interest, as a weak person, not to draw the attention of strong people: 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.

My interest is to be moral, due to the fact that I am physiologically weak and that otherwise society will punish me because of my immorality. Resentment is a psychological sign showing that I am moral only because I am moved by self-interest and not by pure love for duty: my jealousy towards powerful people reveals that I would like to be immoral, like them.

c/ A criticism of the Nietzschean genealogy

Thus, it may be that we have identified the origin of morality as well as of religion: self-interest. It is in my interest to be moral and pious. It is probably true, but Nietzsche does not simply affirm this. At the same time, he considers this origin as a foundation. In other words, the origin of morality is also its foundation (by “foundation of a theory”, I am referring to what makes it true or valuable, according to its normal acceptation). Let us examine in further detail this shift in meaning from the origin to the foundation of morality in order to understand how it occurred in Nietzsche’s thought process.

At first, Nietzsche makes a distinction between the two preceding 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, either my own or from other people (or, more precisely stated—this latter issue was important to me only for the sake of a goal to which it was one path out of many). 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 affirms here that determining the origin of morality is only secondary to a more ambitious project: defining its value – or foundation, to the extent that Nietzsche remarks that if the origin of morality was a mistake (for example, the erroneous opinion of a person about his/her morality), its value would not be diminished: 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.

However, throughout our reading, we must face the facts: Nietzsche never examines the actual question of the foundation of morality and only deals with its origin, which is the point of view from which Nietzsche blames morality, due to an argument, which is not explicitly formulated as such. This is rather surprising since it probably is nothing but the core of the Nietzschean criticism of morality! We may sum up this line of argument as follows: self-interest is the origin of morality, but self-interest is contemptible as it has a negative value. Therefore, morality is also contemptible, as well as worthless.
At first glance, this reasoning seems to be obvious, but it is actually based on a confusion: we cannot admit it, for several reasons.

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