The implications of physical and biological sex differences on sex role behavior cannot be understood without analyzing the complementary role of the sociocultural meaning of sex roles. The normative aspect of gender role behavior is fluid and can be affected by culture, class, and ethnicity. All societies recognize differences between the sexes. The cross-cultural variation in male and female roles does not support the theory that differences are biologically determined. Variations probably result from interrelationships between socioeconomic and cultural influences. Research indicates that lower class children define masculine and feminine characteristics and roles as sharply different while the middle class displays more mutuality in sex role interchange. Research also indicates that ethnicity and cultural heritage influence sex role differences. The level of education and distance between kin will often act to nullify many of the traditional cultural effects, but cultural influences on sex role behavior may be stronger than the socioeconomic influence among some groups. The fact that sex role behavior can be affected by sociocultural factors and that sex differentiation exists does not, however, rule out the concept of equality of opportunity for males and females. (Author/MK)