 According to teleological theories, the contents of mental representations depend, at least in part, on functions, such as the functions of the systems that use or produce them. The relevant notion of function is held to be one used in biology and neurobiology in attributing functions to items, as in “a function of the pineal gland is secreting melatonin” and “a function of brain area MT is processing information about motion”. Proponents of teleological theories of mental content usually understand these functions to be what the items with the functions were selected for, either by phylogenetic natural selection or by some other similar process.