Reproductive competition between females in the matrilineal Mosuo of southwestern China

Abstract

The matrilineal Mosuo of southwestern China live in communal households where brothers and sisters of three generations live together (duolocal residence), and men visit their wives, who reside elsewhere, only at night in 'visiting' marriages. Here we show that these communally breeding sisters are in reproductive conflict, in the sense that they share the resources needed to reproduce. We analyse determinants of reproductive success in females and males, and show that co-resident female kin are in competition; the more female kin reside in the household, the more reproductive success is reduced. Male reproductive success, however, is not determined by the kin in his natal household; duolocal males are not in reproductive conflict with their siblings. Competition with female cousins can be worse than that between sisters. We also find that female work on the farm (which is the main communal resource) is not equal. We use a 'tug-of-war' model of reproductive skew generated by incomplete control, to model the patterns of effort put into competition between sisters and cousins. The model predicts that more dominant (older) sisters will put less effort into reproductive conflict than will less dominant (younger) sisters; but younger sisters will also have lower reproductive success because they are less efficient at gaining access to the shared resource. Both predictions are consistent with our data. Younger sisters work less in the fields than do older sisters, which may represent a form of conflict or may be because their average relatedness to the household is lower than that of their more fertile older sisters.

Female competition and aggression: interdisciplinary perspectives

“…As reported in the current issue by Ji et al [92], the Mosuo of southwestern China are unusual in that neither sex disperses. Instead, brothers and sisters of three generations live together in communal households with matrilineal offspring, and men visit their wives only at night in 'visiting' marriages.…”

“…Instead, brothers and sisters of three generations live together in communal households with matrilineal offspring, and men visit their wives only at night in 'visiting' marriages. Reproductive competition between sisters may therefore result from sharing resources, and Ji et al [92] provide evidence that the reproductive success of Mosou females is negatively influenced by co-resident female kin (see also [93]), with the presence of sisters associated with significantly suppressed fertility and later age at first birth. Consistent with predictions of a 'tug of war' model of reproductive skew, older Mosuo sisters appear to win the conflict and have more offspring than their younger sisters, but they also put more effort into communal farming that supports all the family.…”

Current ecology, not ancestral dispersal patterns, influences menopause symptom severity

“…The Mosuo and Zhaba women display an uncommon duolocal residence pattern with matrilineal descent, where neither sex leaves the natal group for marriage, and descent is traced through the female line. As an alternative to cohabiting marriage, they engage in the practice of zǒu hūn (“walking marriage,” 走婚), in which males and females live in their natal households that comprise of many generations of family members (He, Wi, Ji, Tao, & Mace, ; Ji et al, ; Wu, Ji, et al, ), and men only visit their wives and girlfriends during the night (Cai, ). Men have little or no financial obligations to their spouses or children, and they tend to invest heavily in their sisters' offspring (He, Wu, Ji, Tao, & Mace, ; Ji et al, ).…”

Cultural Evolution of Genetic Heritability

“…Although the nonshared environment is typically discussed as environmental exposure that is specific to the individual, it remains possible that there are multiple layers of communal structure embedded within this variance component. In societies such as the Israeli kibbutzim (Lieblich 2010), the Mosuo of southwest China (Ji et al 2013), the Ache of eastern Paraguay, or the Hiwi of Venezeula (Hill and Hurtado 2009), children are raised communally and the groupings that are relevant for understanding genetic and environmental effects will be configured very differently from how the common environment is operationalized in the typical twin study.…”