 Karen Neander (1991) distinguishes artifact function sharply from biological function. Natural selection acting over the long course of evolutionary history establishes specific effects of biological traits as their functions, in virtue of the reproduction of those traits for those effects. For example, the wings of birds are the result of eons of selection for their effect as airfoils. In contrast, intentional human selection, acting with knowledge and foresight, establishes specific effects of artifacts as their functions immediately, without any reference to a history of reproduction for those effects.