SEX DIFFERENCES IN PASSION AND PLAY HARRY F. HARLOW and HELEN E. LAUERSDORF* Had God created man or monkey each with one identical form and fashion, many problems of pride and passion would never have arisen. Indeed, if that unfortunate celestial decision had been made initially, more than pride and passion would presently fail to exist, for there would never have been more than one man or one monkey. But that was not the decision made, and both species, two sexes, and multiple differences do certainly exist. Even if one merely looks at people, disregarding current clothes and coiffures, anatomical differences can be discerned, and if one merely looks at monkeys, anatomical differences between the sexes are inescapable . In the absence of garments or gossamer it becomes obvious that the sexes differ—even at the level of face validity for males and two-faced validity for females. This, ofcourse, merely means that females are twice as valid and probably four times more reliable than males. Therefore, it is not amazing that anatomical differences between males and females should go completely unquestioned. It is an indisputable biological fact that behavioral differences between the two sexes are many more times as characteristic, diverse, and different from the frigid, frozen, and fatuous differences of anatomy. Thus, it is surprising that sex differences in behavior are questioned and strongly argued by some to be a result of cultural influences only. There are always greater individual and intersexual differences in behavior than in bodies, or in movements than in muscles. Every little movement has a meaning all its own. We would like to discuss differences between the female and male sexes that we have found to hold true after and over many years of research. Our subjects have been rhesus monkeys, man's close relative on the phylogenetic ladder. These sex differences begin at birth and encompass all developmental stages, from early sex reflexes through early sex behavior personal characteristics,juvenile play, the subsequent»Department of Psychology, Primate Laboratory, University of Wisconsin, Madison, Wisconsin 53706. 348 I Harry F. Harlow and Helen E. Lauersdorf · Sex Differences maturation of aggression, and then into adulthood and the roles of parenthood. Infantile Sexual Reflexes There is nothing either subtle or surreptitious about sexual behaviors whether they are studied and measured in babies, in youths, or in people old enough to know better. Let us start with infant sex, uncontaminated by lust or learning. All newborn primates—monkey, ape, and man—are capable of exercising at least two unlearned sexual responses, penile or clitoral erection and pelvic thrusting [I]. The sexual significance ofthese responses is not completely apparent until maturation is combined with meaning at about 3 years of age in the monkey and about 12 years in man. Behaviorally, monkeys grow up or mature four or five times as fast as people, so that sexual interest and capability become apparent in human beings and monkeys at the same stage developmentally, but at a different age chronologically. It can be argued that the aforementioned behaviors do not demonstrate differences between the sexes, since penile and clitoral erection have much in common—extremely common as far as the prudish are concerned. Furthermore, the form of pelvic thrusting in male and female monkeys is very similar. Indeed, in this particular case, the behavior may be more similar than its body basis, since pelvic anatomy was differentially designed to maintain female functions even more biologically important than intermittent intromission. However, both erection and pelvic thrusting behaviors in the neonate differ enormously between sexes in frequency of occurrence, and this is true for both human beings and monkeys. Monkey mothers press naked baby monkeys against their motherly bodies, particularly during nursing , and the male babies thrust against the mother's body with greater frequency and faith than do the females. Sex Differences in Postural Propensities Adequate sexuality does not develop in monkeys until the third or fourth year of life, but long before sex is very adequate it is very evident. For example, we have carefully studied groups of male and female monkeys that, in terms ofdevelopmental age, have been partway toward the benign bliss of connubial constructiveness or competence. In terms of...