Sex Differences in Sexual Motivation in Humans and Other Mammals: The Role of Conscious and Unconscious Processes

Abstract

In self-report questionnaires, men report higher scores than women on variables such as desire for sex, frequency of sexual thoughts, number of sex partners, etc. Based on this, men are considered to have a higher level of sexual motivation than women. However, retrospective self-reports may be unsuitable for estimations of the inherent level of sexual motivation. We review data on automatic (unconsciously controlled) responses and measures of implicit motivation during exposure to sexual stimuli. These responses and measures are inaccessible to willful manipulations and make it possible to determine whether the sex difference in answers to questionnaires is replicated when volitional response manipulations are unlikely. We complement the human data with observations from some rodent and non-human primate species. The attentional resources allotted to stimuli with sexual relevance as well as genital responses to such stimuli are similar in men and women. Measures of implicit motivation also fail to detect any sex difference. Finally, the frequency of masturbation is superior in female infants before the age at which social expectations begin to determine behavior. Neither in rodents nor in non-human primates is there any clear-cut evidence for sex differences in motivation. It seems that males and females are similar with regard to the intensity of sexual motivation. The responses to questionnaires may be affected by social learning of sexual scripts and/or the inferior quality of sexual experiences in women, among other things.

Keywords: automatic (unconscious) responses; genital response; human; implicit motivation; primate; rodent; sexual scripts; volitional responses.

Figure 1

Schematic illustration of the workings of sexual motivation. For explanation, see text. Open, straight arrows illustrate conscious processes in which cognitive evaluations may intervene whereas black arrows indicate automatic (unconscious processes). Curved arrows represent feedback systems. +. stimulation; −, inhibition. Reprinted from [13].

Figure 2

The Columbia obstruction apparatus for study of animal motivation. Diagram of floor plan of the obstruction box. A, entrance compartment; B, obstruction compartment; C, D, divided incentive compartment; E, release plate; di, manually operated door of entrance compartment; dt, automatic door (operated by release plate) between two divisions of incentive compartment. Reprinted from [72]. For a detailed explanation, see the original publication.

Figure 3

Sexual approach behaviors in sexually active, intact male rats and in sexually receptive, hormone-primed ovariectomized rats. The females had been given estradiol benzoate, 25 µg/rat, 48 h before tests, and progesterone, 1 mg/rat, 4 h before. This treatment assures a maximum level of sexual activity. (A) The setup used for quantifying sexual approach behaviors. The rectangles marked A and B delimited the incentive zones. (B) The preference score (time spent in the zone outside the sexual incentive/(that time + the time spent in the zone outside the social incentive)) was obtained during a 10 min test. For female subjects, the sexual incentive was a sexually active male, and the social incentive was a castrated male. For male subjects, the sexual incentive was a sexually receptive female, and the social incentive was another, intact male. There was no difference in score between male and female subjects (t₁₃₄ = 0.314, p = 0.754). (C) The time spent in the zone outside the sexual and the social incentives in male and female subjects. ANOVA showed a main effect of incentive (F_1,134 = 297.89, p < 0.001, ${\eta }_p^2$ = 0.690). The time spent near the sexual incentive was far above that spent in the vicinity of the social incentive. There was no effect of sex (F_1,134 = 3.73, p = 0.055, ${\eta }_p^2$ = 0.027). Even though the sex difference was close to significance, the small effect size shows that it cannot be functionally meaningful. There was an interaction incentive x sex (F_1,134 = 0.029, p = 0.864, ${\eta }_p^2$ = 0.000), showing that the superiority of the sexual incentive was equal in males and females. (D) Speed of movement while moving provides an excellent estimate of the level of locomotor activity. There was no significant sex difference in the activity recorded during the test (t₁₂₂ = 1.836, p = 0.069, Cohen’s d = 0.370). Activity data from 12 females were lost because of a technical failure, but the remaining 34 should offer an acceptable approximation. Data are mean ± SEM.

Figure 4

Illustration of the effect of the basic activity of the sexual central motive state (SCMS) on the choice of mating partner. It can be assumed that sexual incentive value, or sexual attractivity, is normally distributed, as shown in the figure. (A) The activity in the SCMS is low. Only stimuli with very high incentive value, i.e., stimuli produced by highly attractive individuals, are able to activate the SCMS to the degree that genital responses and eventually sexual approach are stimulated. In the example illustrated here, only 2% of potential mates have such a high level of attractivity. The individual is very choosy. (B) Basic activity in the SCMS is high. Even stimuli with low incentive value are able to activate the SCMS, hence sexual approach and visceral responses. As much as 98% of the potential mates have an attractivity level above threshold. The individual shows low, if any, choosiness.