Nietzsche's Genealogy of Morals, ..
Nietzsche was always opposed to a history which saw itself as summing or tracing the development to a culmination, hence an implicit stance outside of time, hence an implicit belief in an eternal truth, a standpoint from which all can be measured. Effective history can evade metaphysics in this way only by seeing history as divergent, incorporating marginalities and disunities, "shattering the unity of man's being." Everything that was thought immortal must be placed within history.
Nietzsche The Genealogy Of Morals Essay 2
If interpretation were the slow exposure of the meaning hidden in an origin, then only metaphysics could interpret the development of humanity. But if interpretation is the violent or surreptitious appropriation of a system of rules, which in itself has no essential meaning, in order to impose a direction, to bend it to a new will, to force its participation in a different game, and to subject it to secondary rules, then the development of humanity is a series of interpretations. The role of genealogy is to record its history: the history of morals, ideals, and the metaphysical concepts, the history of the concept of liberty or of the ascetic life; as they stand for the emergence of different interpretations, they must be made to appear as events on the stage of historical process. (86)
A genealogy, on the other hand, of values, morals, knowledge, will never confuse itself with a quest for their 'origins' but will cultivate the details and accidents that accompany every beginning.