 An account of human nature that is essentialist in this sense would take the nature of the human natural kind to be a set of microstructural properties that have two roles: first, they constitute an organism’s membership of the species Homo sapiens. Second, they are causally responsible for the organism manifesting morphological and behavioural properties typical of species members. Paradigms of entities with such natures or essences are chemical elements. An example is the element with the atomic number 79, the microstructural feature that accounts for surface properties of gold such as yellowness. Applied to organisms, it seems that the relevant explanatory relationship will be developmental, the microstructures providing something like a blueprint for the properties of the mature individual. Kripke assumed that some such blueprint is the “internal structure” responsible for the typical development of tigers as striped, carnivorous quadrupeds (Kripke 1972 [1980: 120f.]).