International Journal of Comparative Psychology

The purpose of this study was to investigate male preference and to define the aspects of females that affect male preference. We set experimental conditions that enabled us to measure successful mating by gathering sperm from female vaginal washings and observing sexual behavior. The animal subjects in our study were cynomolgus monkeys, all of whom were bred in our primate institute. During the study, one male would be grouped with two females, each of whom lived in a cage adjacent to the male’s cage. This enabled each of the females to be housed with the male in turn; 12 males and 24 females were included in the study. After a male was housed with a female, we observed through a microscope the existence of sperm in the female’s vaginal washing, thus confirming copulation success. In some of the groups, behavioral observation was conducted on both the male and female subjects. According to our findings, in the multiparous females, successful mating was observed on 29% of cohabitation days. Among nulliparous females, the presence of sperm was observed on only 6% of cohabitation periods. Some 66.7% of nulliparous females never mated with a male. Our observations also revealed that sexual behaviors were more frequently observed when a male lived with a multiparous female. “Male-grooming-of-female” activities were seen more frequently between a male and multiparous female; that is, the male approached a multiparous female for copulation by grooming her. Our study suggests that male cynomolgus monkeys prefer multiparous females, as it is important that a male choose a female who more easily and regularly becomes pregnant and gives birth to offspring with a higher survival rate. Thus, male choice is biologically significant with respect to leaving more offspring.