The More Things Change: Husband's Income, Wife's Income, and Number of Biological Children in the U.S.

Consider the word “husband.” It derives from two words, “hús “(from the Old Norse for house) and “bóndi” (from the Old Norse for occupier and tiller of the soil), and its original meaning was a man who had a home and therefore could marry and support a family.¹ The word thus embodies a principle common in preindustrial England and Europe “that a man might not marry until his living was assured.”²

Today, this principle is often referred to as the “male breadwinner norm.” In the U.S., over half of all married couples are dual-earner couples,³ so this principle may seem something of a historical relic. Yet in practice this does not seem to be the case. Evidence from the U.K., U.S., and Europe suggests that for men, the link between making a living and having a family still exists. Men with high personal incomes are more likely to have biological children than men with low personal incomes, mostly because of greater childlessness among low-income men.⁴ Despite the rise of dual-earner couples, the same is not true for women; in fact, the opposite is usually true—women with high personal incomes are less likely to have biological children than women with low personal incomes, although there is some evidence that this is changing in recent cohorts in Scandinavia. 

Given the fact that over half of married couples in the U.S. are dual-earner couples and that the majority of childbearing takes place within married-couple families, how do these opposing effects of personal income influence the fertility of men and women in these families?  In my new research published in Biodemography and Social Biology, I examined this question using data from the 2014 wave of the Survey of Income and Program Participation (SIPP).⁵ The SIPP contains information on men’s and women’s personal incomes from all sources (including wages, pensions, government programs, business income and investment income) in addition to their number of biological children. For men and women who were currently married and living with their spouse, I examined the effect of personal income together with their spouse’s income on their number of biological children. The effects of age and years of education as well as racial and ethnic background were controlled.⁶

I found that for husbands, personal income was positively associated with their number of biological children, and for wives, personal income was negatively associated with their number of biological children, as previous research has shown. That is, husbands with higher income tended to have more children, while wives with higher income tended to have fewer children. 

Additionally, the more a man’s wife earned, the fewer children he was likely to have, and the more a woman’s husband earned, the more children she was likely to have. This was true for the entire sample as well as for the subset of men and women aged 45-65, who likely have completed fertility but are unlikely to be retired. This was not because of childlessness among low-income men and high-income women, but also held true for all those with children. For almost all the analyses, these findings held true regardless of whether or not education was controlled, i.e., held constant.

These results indicate that men earning high incomes with a spouse who has a low income have the most biological children in the United States, while women with low incomes with a spouse who earns a high income have the most biological children. These differences are not large—as very few people in the U.S. have large numbers of children—but they exist, nonetheless. For women, there is likely reverse causation as women who have children tend to work less outside of the home, which would mean lower income. Women with children may also experience wage discrimination. There may be reverse causation for men also, as men with children may try to earn more or may experience positive wage discrimination.

Even so, these results suggest that for men in the U.S., fathering children is still related to being able to provide, as it has been historically. For women, husband’s income remains important for childbearing. My study was based on data collected in 2014 when fertility rates in the United States were very low and falling. In 2021, the U.S. population grew at the slowest rate since the founding of the nation, in part due to historically low fertility rates.⁷ The findings presented here suggest that the decline in the proportion of men employed full time⁸ and the decline in male earnings relative to female earnings⁹ likely have contributed to the decline in aggregate fertility rates. Given the positive relationship between education and earnings, lower rates of men attending college are likely to exacerbate these tendencies in the near future, with a continuing downward pull on fertility rates. 

Rosemary L. Hopcroft is Professor of Sociology at the University of North Carolina at Charlotte. She is the author of Evolution and Gender: Why it matters for contemporary life, (Routledge 2016) and editor of The Oxford Handbook of Evolution, Biology, & Society (Oxford, 2018). 

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1. Oxford English Dictionary. Edited by Angus Stevenson. (Oxford: Oxford University Press, 2010).

2. Petersen, W. 1960. “The Demographic Transition in the Netherlands.” American Sociological Review 25:334-347.

3. U.S. Bureau of Labor Statistics. 2017. Women in the labor force: a databook. Available: https://www.bls.gov/opub/reports/womens-databook/2017/pdf/home.pdf

4. Nettle, D., and T. V. Pollet. 2008. Natural selection on male wealth in humans. The American Naturalist 172 (5):658–66; Barthold, J. A., M. Myrskylä, and O. R. Jones. 2012. Childlessness drives the sex difference in the association between income and reproductive success of modern Europeans. Evolution and Human Behavior 33:628–38; Fieder, M., and S. Huber. 2022. Contemporary selection pressures in modern societies? Which factors best explain variance in human reproduction and mating?. Evolution and Human Behavior 43:16–25. 

5. Hopcroft, Rosemary L. 2022. Husband’s income, wife’s income, and number of biological children in the U.S. Biodemography and Social Biology. Published online.

6. Number of children could differ for husband and wife because I measured each person’s number of biological children, which was not necessarily the same as the number of children they had with their current spouse. However, I also ran the analysis for husbands and wives who were married and in their first marriage, in which case the children of the wife were likely children of the husband, and vice versa. This did not change the results. 

7. Rogers, Luke. 2021. COVID-19, Declining Birth Rates and International Migration Resulted in Historically Small Population Gains. Available: https://www.census.gov/library/stories/2021/12/us-population-grew-in-2021-slowest-rate-since-founding-of-the-nation.html

8. Ullrich, L. D. 2021. Male Labor Force Participation: Patterns and Trends. https://www.richmondfed. org/-/media/RichmondFedOrg/publications/research/econ_focus/2021/q1/district_digest.pdf

9. Shrider, E. A., M. Kollar, F. Chen, and J. Semega. 2021. U.S. Census Bureau, Current population reports, P60-273, income and poverty in the United States: 2020, U.S. Government Publishing Office, Washington, DC, September 2021.