Often decried, polygyny may sometimes have advantages

But a new study of polygyny in Tanzania finds that the practice of sharing a husband may, in some circumstances, lead to greater health and wealth for women and their children.

UC Davis anthropologist Monique Borgerhoff Mulder and colleagues compared polygynous and monogamous households in 56 villages in northern Tanzania, where polygyny is widespread among certain ethnic groups, including the Maasai.

When comparing households within individual villages, polygynous households often had better access to food and healthier children. Polygynous households also owned more cattle and farmed more land than monogamous households. These findings support evolutionary anthropological accounts of marriage indicating that polygyny can be in a woman's strategic interest when women depend on men for resources.

"If you have a choice of a guy who has 180 cows, lots of land and other wives, it might be better for you to marry him rather than a guy who has no wives, three cows and one acre," Borgerhoff Mulder said.

Consistent with prior research, the study found that polygyny was associated with low food security and poor child health when looking at data across all villages. However, this pattern was accounted for by the tendency of polygyny to be most common in ecologically vulnerable and marginalized ethnic groups. This error of interpretation is known as the "ecological fallacy," and flaws all previous analyses of large data sets like the Demographic and Health Surveys.

"Our study suggests that highly polygynous, predominantly Maasai, villages do poorly not because of polygyny, but because of vulnerability to drought, low service provision and broader socio-political disadvantages," said David Lawson, a population health lecturer at the London School of Hygiene & Tropical Medicine and lead author of the study published in the Proceedings of the National Academy of Sciences.

Tanzania faces a high burden of food insecurity and malnutrition: 45 percent of children are of low height for their age, indicating chronic malnutrition with long term impacts on physical and cognitive development. Previous research by Lawson, Borgerhoff Mulder and colleagues showed that nearly 60 percent of Tanzanian Maasai children experience stunting.

The United Nations states that polygyny contravenes a woman's right to equality with men and can have such serious emotional and financial consequences for her and her dependents that such marriages ought to be discouraged and prohibited.

However, the researchers highlight the importance of local context in studying the health implications of cultural practices, and suggest that in some settings, prohibiting polygyny could be disadvantageous to women by restricting their marriage options.

"The issue is not the number of partners," Borgerhoff Mulder said. "Women should be assured the autonomy to make the decisions they want""

The study is limited to food security and health, and cannot tell us about the wider potential for polygyny to cause harm, the researchers said. They also note that polygyny was only associated with superior outcomes when fathers and children were co-resident: outcomes for other polygynously-married women were indistinguishable from those of monogamous women. This suggests that any potential benefits of sharing a husband may be limited to the primary wife within a polygynous marriage.