Psychological adaptation to human sperm competition

Abstract

Sperm competition occurs when the sperm of two or more males simultaneously occupy the reproductive tract of a female and compete to fertilize an egg. We used a questionnaire to investigate psychological responses to the risk of sperm competition for 194 men in committed, sexual relationships in the United States and in Germany. As predicted, a man who spends a greater (relative to a man who spends a lesser) proportion of time apart from his partner since the couple's last copulation reported (a) that his partner is more attractive, (b) that other men find his partner more attractive, (c) greater interest in copulating with his partner, and (d) that his partner is more sexually interested in him. All effects were independent of total time since the couple's last copulation and the man's relationship satisfaction. Discussion addresses two failed predictions and directions for future work.

Absence makes the adaptations grow fonder: Proportion of time apart from partner, male sexual psychology, and sperm competition in humans (Homo sapiens).

“…The results of the current research are consistent with the results of previous research investigating adaptation to sperm competition in humans, notably Shackelford et al (2002) and Gallup et al (2003). Gallup and his colleagues, for example, predicted and documented relationships between a man's suspicions of his partner's sexual infidelities, physical separation from his partner, and a man's copulatory behaviors upon physical reunion with his partner (e.g., engaging in deeper copulatory thrusting following physical separation).…”

“…The proportion of time the couple had spent apart since their last copulation was calculated by subtracting the number of hours that the couple had spent together since their last copulation from the total number of hours since the couple's last copulation and dividing this difference by the total number of hours since the couple's last copulation (following Shackelford et al, 2002; also following Baker & Bellis, 1989, 1993, 1995Starratt et al, in press) Shackelford et al, 2002). Distress following partner's denial of a request for copulation (␣ ϭ .89) is the mean of responses to three items: (a) anger following his partner's denial of his request for copulation, (b) frustration following his partner's denial of his request for copulation, and (c) upset feelings following his partner's denial of his request for copulation (following Shackelford et al, 2002).…”

“…Distress following partner's denial of a request for copulation (␣ ϭ .89) is the mean of responses to three items: (a) anger following his partner's denial of his request for copulation, (b) frustration following his partner's denial of his request for copulation, and (c) upset feelings following his partner's denial of his request for copulation (following Shackelford et al, 2002). Persistence following his partner's denial of his request for copulation (␣ ϭ .55) is the mean of responses to two items: (a) persistence in having sex with his partner following his partner's denial of a request for copulation and (b) change in interest in sex with his partner following his partner's denial of a request for copulation.…”

“…These perceptual changes may motivate men to copulate as soon as possible with their partner, thereby entering their sperm into competition with any rival sperm that may be present in her reproductive tract. Shackelford et al (2002) also predicted that proportion of time spent apart would correlate positively with distress following a partner's denial of his request for copulation with her. This prediction, however, was not supported statistically.…”

Sex Differences in Sexual Psychology Produce Sex-Similar Preferences for a Short-Term Mate

“…Inseminating more sperm following a separation may function to outnumber or "flush out" rival sperm in the female reproductive tract (Baker & Bellis, 1995;Parker, 1970). Reasoning that there must be psychological adaptations accompanying these physiological adaptations, Shackelford et al (2002) demonstrated that men who spent a greater (relative to men who spent a lesser) proportion of time apart from their partner since the couple's last copulation rated their partners to be more physically attractive and showed greater interest in copulating with their partners. Such psychological adjustments may motivate men to copulate with their partners as soon as possible, placing their sperm in competition with rival sperm that may be present.…”