Instinct and Drive
Lacan follows Freud in distinguishing the instincts from the drives, and criticizing those who obscure this distinction by using the same English word ("instinct") to translate both Freud's terms (Instinkt and Trieb). "Instinct" is a purely biological concept and belongs to the study of animal ethology. Whereas animals are driven by instincts, which are relatively rigid and invariable, and imply a direct relation to an object, human sexuality is a matter of drives, which are very variable and never attain their object. Although Lacan uses the term "instinct" frequently in his early work, after 1950 he uses the word less frequently, preferring instead to reconceptualize the concept of instinct in terms of need.
Biology and Social and Cultural Factors
From his earliest works, Lacan criticizes those who attempt to understand human behavior purely in terms of instincts, arguing that this is to suppose a harmonious relation between man and the world, which does not in fact exist. The concept of instinct supposes some kind of direct innate knowledge of the object which is of an almost moral character.
Against such ideas, Lacan insists that there is something inadequate about human biology, a feature which he indicates in the phrases "vital insufficiency" (insuffisance vitale). and "congenital insufficiency". This inadequacy, evident in the helplessness of the human baby, is compensated for by means of complexes. The fact that human psychology is dominated by complexes (which are determined entirely by cultural and social factors) rather than by instincts, means that any explanation of human behavior that does not take social factors into account is useless.