The nature-nurture debate in psychology deals with the extent to which bodily, behavioral and mental traits can be attributed to internal, fixed, predetermined factors (“nature”) versus external, environmental factors (“nurture”). In the history of philosophy, the nature-nurture debates were centered on the notions of species-wide instincts in animals and innate knowledge in humans. It was not until the nineteenth century that the nature-nurture debates were extended to explaining individual differences. The nature-nurture dichotomy, however, has faced numerous challenges. There is no consensus on how to conceptualize innateness, and the empirical evidence for innateness has long been challenged and remains controversial. Despite these problems, most psychologists assume that that developmental of any psychological trait involves the contributions from both nature and nurture which are presumed to be separable sources of influence. Others, particularly those studying development, see the traditional dichotomy as fundamentally flawed and counterproductive.