Women would like their partners to be more synchronized with them in their sleep-wake rhythm.

Men sleep shorter and go to bed and get up later than women, thus they are later chronotypes. This difference between the sexes is most pronounced between puberty and menopause indicating the possibility that morningness is subject to sexual dimorphism related to reproductive aspects. The objective of the study was to compare the sleep-wake behavior of women with their actual partners and with their preferred partners. As a hypothesis, we expect some assortment in mating concerning chronotype (with the actual partner), but we also expect a higher synchronization with a preferred ideal partner. 167 women were analyzed in this study (mean age: 23.0 ± 2.57 (SD) years). Mated women were earlier chronotypes than their partners (t = -2.051, p = .042, d = .34) but the difference was small (11:02 min ± 1:04 min). The results of the present study showed women preferring a partner synchronized to their own sleep-wake-rhythm more than their actual partners were. The above result was true either for single facets of the sleep-wake rhythm (e.g. bed time, sleep onset) or for midpoint of sleep on free days - an indicator of actual chronotype: women's and their partners' correlation of midpoint of sleep was lower (r = .513) than women's and their ideal partners' correlation (r = .855). Amongst various sleep-wake measures, women particularly preferred a partner going to bed at the same time. Assortative mating according to sleep-wake rhythm exists, but women for long-term pair-bonds would like their partners far more synchronized.