Psychological Sex DifferencesOrigins Through Sexual SelectionDavid M. BussUniversity of MichiganMen and women clearly differ in some psychological do-mains. A. H. Eagly (1995) shows that these differencesare not artifactual or unstable. Ideally, the next scientificstep is to develop a cogent explanatory framework for un-derstanding why the sexes differ in some psychologicaldomains and not in others and for generating accuratepredictions about sex differences as yetundiscovered.Thisarticle offers a brief outline of an explanatory frameworkfor psychological sex differences—one that is anchored inthe new theoretical paradigm of evolutionary psychology.Men and women differ, in thisview,in domains in whichthey have faced different adaptive problems over humanevolutionary history. In all other domains, the sexes arepredicted to be psychologically similar. Evolutionary psy-chology jettisons the false dichotomy between biology andenvironment and provides a powerful metatheory of whysex differences exist, where they exist, and in what contextsthey are expressed (D. M. Buss, 1995).Evolutionary psychology predicts that males and fe-males will be the same or similar in all those do-mains in which the sexes have faced the same orsimilar adaptive problems. Both sexes have sweat glandsbecause both sexes have faced the adaptive problem ofthermal regulation. Both sexes have similar (although notidentical) taste preferences for fat, sugar, salt, and partic-ular amino acids because both sexes have faced similar(although not identical) food consumption problems.Both sexes grow callouses when they experience repeatedrubbing on their skin because both sexes have faced theadaptive problem of physical damage from environmentalfriction.In other domains, men and women have faced sub-stantially different adaptive problems throughout humanevolutionary history. In the physical realm, for example,women have faced the problem of childbirth; men havenot. Women, therefore, have evolved particular adapta-tions that are absent in men, such as a cervix that dilatesto 10 centimeters just prior to giving birth, mechanismsfor producing labor contractions, and the release of oxy-tocin in the blood stream during childbirth.Men and women have also faced different infor-mation-processing problems in some adaptive domains.Because fertilization occurs internally within the woman,for example, men have faced the adaptive problem ofuncertainty of paternity in putative offspring. Men whofailed to solve this problem risked investing resources inchildren who were not their own. All people descend froma long line of ancestral men whose adaptations (i.e., psy-chological mechanisms) led them to behave in ways thatincreased their likelihood of paternity and decreased theodds of investing in children who were putatively theirsbut whose genetic fathers were other men. This does notimply, of course, that men were or are consciously awareof the adaptive problem of compromised paternity.