Systematics is the science that produces systems to order biodiversity and to name the categories it produces. These categories, families, genera, species, races, etc., resulting from a more or less continuous differentiation process, are unclear by nature. They imperfectly reflect reality: the existence of more or less divergent lineages. Within the human species, like in any other, differences exist. Their existence would not be a scientific problem if it did not entail hierarchization and essentialization which are of no concern to biology.