Two things prompted this article.
First was a WhatsApp debate among former law-school classmates about monogamy, polygamy and mpango wa kando (side chicks). The monogamists were the majority, but their defence was often: "God said so."
If monogamy is a useful institution, it should also be defensible through logic, history and economics.
Second was this week's viral story of a senior county employee whose alleged son, born outside marriage, went to social media to complain about neglect.
Whatever the truth of that case, the problem is familiar: one income, competing households, children who experience the consequences.
This is not an attack on African culture, nor a claim that every family with multiple households is dysfunctional. It is an argument about what happens when one person creates several sets of obligations without creating several sets of resources.
The logic begins with biology. Human populations produce slightly more boys than girls at birth — roughly 105 boys per 100 girls. Because males experience higher mortality, adult populations move closer to parity. Adult societies tend toward roughly one man for one woman.
Marriage is, among other things, a matching system.
Imagine 100 adult men and 100 adult women. Under monogamy, marriage is distributed relatively evenly. No man can convert wealth into a legal claim on several women.
Now suppose 10 men each form three households. Those 10 men account for 30 women, leaving 90 men to compete for the remaining 70.
Real life is more complicated. People marry at different ages, divorce, remarry and migrate. But the principle remains: where some men can concentrate access to marriage, access becomes more unequal. That concentration has security consequences.
A large body of research, most comprehensively by anthropologist Joseph Henrich and colleagues at UBC, finds that where marriage is highly concentrated among a small number of men, levels of social strain rise — higher rates of kidnapping, assault and other conflict. Political scientists Hudson and den Boer show the same for skewed sex ratios: when many young men cannot form households, risk-taking and conflict increase.
Old Africa understood this logic in reverse. Among many pastoralist communities, from Turkana and Samburu to Maasai, oral histories are full of raids for women. Those raids were not random. They are what happens when marriage becomes concentrated. When a small number of powerful men in a village hold many wives, bride price rises, and many young men cannot marry locally. They have two choices: remain unmarried without standing, or raid a neighbouring community for women and livestock for bride wealth. The concentration of women among a few men in one place created the incentive to capture women from another place. Monogamy, in that context, was a peace pact: let every young man marry locally, and he will defend the village instead of attacking his neighbour.
Women are not cattle. They are not land. They are not assets whose quantity a man can increase because he has wealth.
A man who owns ten houses has accumulated property. A man who forms ten households has entered into relationships with ten human beings.
Where wealth increases access to multiple households, economic inequality becomes inequality in family formation.
Monogamy interrupts that conversion. It tells the wealthy man: your money is yours, but people are not your wealth.
Monogamy is older than Christianity. Rome developed a strongly monogamous legal tradition while other societies permitted different arrangements. Marriage has never been merely romance. It determines inheritance, property and responsibility for children.
Rome understood this. By the late Republic, elite men were avoiding marriage and birthrates collapsed. Augustus did not preach. He legislated. In 18 BC, the Lex Julia penalised celibacy and rewarded fathers of three children with faster promotion and inheritance privileges. He understood empire is not sustained by conquest alone but by households.
That idea returned 1,800 years later. Both the American and French Revolutions declared that no man is born with more rights by blood. Christianity had said souls are equal before God. The Enlightenment said citizens are equal before the law. Monogamy became the domestic expression of that equality: one man, one vote, one household.
Consider a man earning Sh100,000. With one household, that income covers housing, food, fees, healthcare, transport and savings.
Now divide it between two households. Income has not doubled. Obligations have. Two rents, two sets of bills, multiple fees and transport. One income cannot be spent twice.
This is where economist Melissa Kearney's "two-parent advantage" matters. Two committed adults can pool income, time and skills.
Multiple households complicate that. A father may have children in three homes, but he cannot be in three homes at once. The father is not multiplied. He is divided.
Same with inheritance. Ten acres divided between two children gives five each. Divided among six, each gets about 1.67 acres. When dependants grow faster than assets, each share shrinks.
US Census data shows Indian Americans are the highest-earning ethnic group at $152,341 median household income in 2022, with Chinese Americans at $101,728. Asian households remain highest at $112,800 while Black households remain lowest at $56,490 in 2023.
These communities also show very stable marriage patterns. Pew finds Asian Americans are least likely to have experienced divorce at 16 per cent, Black adults most likely at 41percent. This is not genetic. It is arithmetic: W/n, wealth divided by fewer claims, reaches critical mass for a university, a home, a business.
China provides a nuanced natural experiment. When it imposed the one-child policy in 1980, families were required, often harshly, to put resources into one household and one child. That cohort entered an economy that was liberalising. Income rose from $194 per capita in 1980 to over $10,000 by 2020. That rise was factories and markets, not just family. But the family mechanism is instructive: concentration allowed investment to reach critical mass.
That is the link between capitalism and monogamy. Capitalism rewards concentrated capital. Households with one rent and one set of fees are more likely to save and invest in one place. Households split across several doors spend on maintenance, not accumulation.
Monogamy does not make people equal. It prevents inequality of wealth from becoming unlimited inequality of access to marriage, and inequality of access from becoming instability.
One man, one wife. Not because relationships are simple. But because human beings are equal.
