Sex needs recognition and synchronization. Many levels are found, from chemical cell recognition to mirror neurons which anticipate actions and emotions of a partner. Some animals recognize species, but not sex. Many more recognize sex, but not individuals. Individualized sex and/or social relations are only found in birds and mammals. Imprinting defines sex objects and goals, stereotyped or flexible, according to species. In humans, sex imprinting conditions sex orientation, practices and response to contradictory prescriptions of personal drives, social rules, fashion, medias and life history's contingencies.