Assortative mating in morningness-eveningness.

Individuals differ in their morningness-eveningness preference (circadian preference); that is, some prefer morning hours for intellectual and physical activities and others prefer late afternoon or evening hours. This has been viewed as an interesting facet of personality. Assortative mating has been studied in personality research, but assortative mating in circadian preference has rarely been examined. Eighty-four couples participated in this study. They filled in the Composite Scale of Morningness; they also supplied data about rise times and bedtimes as well as information about relationship satisfaction and duration. The results revealed a moderate positive relationship between couple partners in morningness-eveningness which persisted after correcting for age. Similarly, correlations existed between the sleep-wake variables (rise time and bedtime) on weekdays and on the weekends, the association being higher for weekends. There was no significant correlation between length of the relationship and dissimilarity in morningness-eveningness, suggesting that the above-reported correlations reflect an initial assortment rather than convergence effects. Further, no significant correlation was found between dissimilarity in morningness-eveningness and relationship satisfaction. The results suggest that assortative mating in morningness-eveningness is likely and is probably based on an initial assortment. The likelihood to meet and mate may also be linked to chronotype. When differences in circadian preferences exist between possible partners, this reduces the likelihood that these persons meet either by accident or during work and leisure activities. Therefore, two extreme chronotypes are unlikely to meet each other because they have the smallest overlap in their preferred active time during the day due to the circadian rhythmicity.