Monogamy or polygamy: An economic choice?

Except in a few special communities, monogamy is practised in almost all societies today. This makes it seem as if monogamy is a human instinct. In Chinese culture, fidelity between a couple and support through hard times is often symbolised by animals such as the Mandarin duck. Family elders would gift couples on their wedding day with Mandarin duck linen sets, conveying their blessings. The swan goose also symbolises fidelity; it is believed to be the most monogamous creature in the animal kingdom as it mates for life.

However, references to chastity and such are just projections of mankind's impressions onto the natural world. Our idea of being "one with nature" often gives rise to such baseless projections. The breeding season of Mandarin ducks begins around April and this is when male and female Mandarin ducks swim in pairs and seem inseparable. Perhaps such scenes left a deep impression on ancient literati. But alas, the beautiful imagery ends here.

When mating season starts in May, the male ducks go all out to win the attention of the female ducks, while the latter cling to the former too. However, as soon as they have mated, the male ducks would exit the scene, leaving the female duck to build the nest, hatch the eggs and take care of their offspring alone. Putting aside the fact that male Mandarin ducks seek out different female Mandarin ducks every year, even in the same breeding season, researchers from Jilin province's Changbai Mountains area discovered very early on that when either among a pair of Mandarin ducks is shot dead, the other one quickly finds a new partner. As for the swan geese, while they take care of their offspring together, they leave their partners as soon as mating season is over in late summer, and look for a new partner the following year. It is not true that they mate for life.

Animals evolve to have the best chance of reproducing and leaving behind their genes. Among the over 8,000 bird species in the world, roughly 90% of them mate and take care of their young together, meaning that they are monogamous. This is because birds take a long time to incubate their eggs and rely on their partner to bring them food, or risk starving to death. However, ornithologists have discovered that even birds among the monogamous species do mate with other birds, not just their partners. In other words, they do cheat, as alluded to in Helen Fisher's Anatomy of Love: A Natural History of Mating, Marriage, and Why We Stray.

Human evolution is a type of cultural evolution and monogamy is the product of production incentives. Gary Becker was an economics professor at the University of Chicago and a renowned economic imperialist in contemporary Western social sciences academic circles. He was known for his unique insights into the economic analysis of human behaviour and received the Nobel Memorial Prize in Economic Sciences in 1992. His research focused mainly on marriage and family.

When using economic approaches to analyse "why one man is typically married to one woman" in his paper "A Theory of Marriage", Becker explained, "The importance of own children is sufficient to explain why marriages of several men to one or several women are uncommon since it would be difficult to identify the father of a child if many men had access to the same woman, whereas the identity of the mother is always known."

Becker's affirmation of modern society's practice of monogamy is based on an important premise that, in a male-dominated society, the husband is the family's main source of income, and thus has greater control over family property and greater decision-making power in distributing assets after death. Because males hold the power to distribute assets in the family, it is important for fathers to know who their "own children" (biological children) are in the family.

If a child in the family is not their biological child and the father knows nothing about it, it would result in two serious consequences for the men: one, the father would end up taking care of non-biological children, allowing "outsiders" to have a share of the family's income; and two, after the father passes away, the family's assets could be inherited by "outsiders". These serious consequences pose major threats to the accumulation of family assets and investments in their children's human capital.

Since monogamy is so economically sound, why does polygamy still exist in the world today? My doctoral supervisor Professor Shi Jinchuan of Zhejiang University is an expert in law and economics. He addressed this question in an interesting way in his book The Taste of Law and Economics (《法律经济学趣谈》), which I paraphrase here.

The Mosuo people living on the banks of Lugu Lake, which borders China's Sichuan and Yunnan provinces, is one of the world's last matriarchal societies. In history, they adopted a "walking marriage" (走婚) system where men and women did not marry and the women chose and swapped partners as they wished.

In such a system, a man who has feelings for a woman (and she for him) would stay over at the woman's house at night and return to his own home the next morning. Neither of them would be considered the other's family, and they wouldn't form a new and independent family through this union either.

In a "walking marriage", the male and female call each other "A Xiao" (阿肖). Based on local customs, everyone can have unlimited "A Xiaos". While this marriage system has undergone major changes in today's society, it is essentially still polygamous. But under such a system, how is the father to identify his "own children"? While this seems like a challenging question, the answer is very simple: fathers do not have to do so under this system.

In the Mosuo matriarchal society, women have familial power and control over the family's properties. If we think of their societal structure as a joint-stock company, the company's shareholders are all women - from the grandmothers, mothers and aunties to the sisters - while the employees are all men - from the granduncles and uncles to the brothers.

In a Mosuo family, children only belong to their biological mother and have no financial relationship with their biological father. Since the father does not live with his biological children and is not responsible for raising them, he has no control over the assets of the family where his biological children live. Thus, it becomes meaningless for fathers to recognise their "own children". Women on the other hand have no problem identifying her own children, since they are the ones who gave birth to them. Thus there is no question of the family's income or assets landing in the hands of outsiders.

Now let's turn to polyandry, which is still practised in contemporary Indian society.

The Jat people in India's Uttar Pradesh still practise polyandry today. Basically, a wife's many husbands are brothers, that is, the Jat people's practice of polyandry refers to a marriage system where brothers share the same wife. There are about 1,500 unmarried males who live with their brothers and share a wife in Uttar Pradesh's three districts of Meerut, Baghpat and Muzaffarnagar. Such polyandry continues because the property of the Jat people belongs to the whole family of brothers - it is not, and also will not be, divided among the individual brothers of the family. As a result, there is no need for any of the brothers or husbands to identify their own children. To put it crudely, what matters is that the children come from the brothers of the same family.

In fact, in areas under different social environments and property regimes - such as in Tibet or other ethnic minority areas in China - there had been instances of polyandrous marriages in the past as well. Historically, the Monpa people in Northeast India practised polyandry to pay lower taxes. If three brothers each married their own wives and formed three independent families, they would have to pay three sets of taxes. But a family formed by brothers sharing one wife need only pay one tax as a single family unit. Thus, marriage has become a means of tax evasion.

The economic analysis of different marriage systems shows that such systems are subsets of other systems in human society and cannot exist independently of other social institutions. In particular, family assets management has an important influence on marriage systems. What various marriage systems have in common is that they prevent the outflow of a married couple's income and assets. Any marriage system that fulfils that criteria in the easiest and most inexpensive way can be said to be an economically efficient marriage system that has passed the cost-benefit analysis.

In terms of making the best choice under economic constraints, society's asset management system is an important factor governing people's choice of marriage system. And because this constraint is different in different societies, people are able to choose among different marriage systems, be it monogamy or forms of polygamy.

This article was first published in Chinese by Caixin Global as "为什么现代社会实行一夫一妻制". Caixin Global is one of the most respected sources for macroeconomic, financial and business news and information about China.

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