The link between prosperity and family-formation is one of the oldest observations of population studies. In the 18th century, Thomas Malthus wrote that the natural tendency of any population is to explode, and the only thing keeping it in check is the limited food supply. As food and resources become more available, couples form and have children. This is a politically charged topic, with all sorts of implications for welfare and women's reproductive freedom. Indeed, Malthus went on to gain eternal notoriety by suggesting that the poor should not be helped, since it would only breed more of them anyway.

Since then, sociobiologists have identified many other factors that affect family-formation as well. They include religious, cultural and sexual values, education, access to birth control, women's freedom, desperation among the teenage poor, welfare, the average age of the rest of the population, the death rate, and many other things. Of all these factors, however, prosperity still remains the most significant in affecting family-formation and birthrates.

The history of economic booms and slumps in the world is also a history of its population booms and slumps as well. The Great Depression saw an equally great drop in the birthrate (18.4 per 1,000 women per year). By contrast, the economic boom of the 50s was accompanied by an equally dramatic Baby Boom (25.3 per 1,000 women in 1957).1 In fact, the world's population explosion in the last 200 years - from 1 to 6 billion - was only possible thanks to the scientific and industrial revolutions, which solved many problems of scarcity.

The correlation between prosperity and childbirth exists not only on a global level, but on a family level as well. The following Census table shows the 1992 income distribution of households and families. Households are defined as any collection of people living under one roof; families are defined as married couples (with or without children), single parents, or relatives. There are about 96 million households in the U.S., of which 68 million are families, but it is their distribution which is most revealing:

1992 Income Distribution of Households and Families (includes government assistance):2

Income               Households   Families
Under $10,000        14.6%         9.5
10,000 - 14,999       9.5          7.3
15,000 - 24,999      16.8         15.5
25,000 - 34,999      14.8         15.0
35,000 - 49,999      17.1         19.2
50,000 - 74,999      16.1         19.6
75,000 and over      11.0         13.9

As you can see, there is a higher percentage of families in the richest households. Conservatives and liberals argue over which causes which; Dan Quayle maintains that "marriage is perhaps the best anti-poverty program of all." Liberals claim he has this backwards: that poverty is the best anti-marriage program of all. Who's right? Before reviewing the relevant statistics, many might guess the answer intuitively, by asking: do women prefer men who are successful, who can support a family and who show potential for monogamy? Or do women marry men without preference for their status or potential for monogamous support, because marriage fulfills these things?

Sociobiology is the field that covers these questions, and according to its scientists, the first question is the correct one. In America, men who marry in a given year earn about 50 percent more than men of the same age who do not.3 The reason is because women must be careful and selective. The possibility of pregnancy means that a woman cannot take sexual encounters or mating choices lightly. She must not only be careful to select a man who will stay in the relationship, but have the means to support a child and the willingness to provide it. A poor choice may mean inadequate help and the death of her child.

Humans are quite different from other animals, of course, but a comparison between them is revealing. Science writer Mary Batten reports: "The clearest form of female choice [in the animal kingdom], the one for which the largest body of evidence exists, is selection for resources - material benefits above and beyond the basic contribution of sperm."4 Females prefer males who are fatter, offer larger mating gifts, possess the most fruitful territories, or show physical traits which make food-collection easier. Males who offer less in these areas tend to be spurned.

In humans, sociobiologists have consistently found that women prefer men of means in all cultures and civilizations around the world. (In societies where match-makers arrange marriages, the same considerations still apply.) Anthropologist John Hartung, who analyzed data from some 850 societies, summed up his findings: "The data... say that females go with the money, which is parental investment on the part of males."5 Women are also attracted to cues of wealth, such as intelligence or status. Psychologist Bruce Ellis conducted a cross-cultural study of female preferences and reported: "For women the world over, male attractiveness is bound up in social status, or skills, strength, bravery, prowess, and similar qualities."6 Again, there are numerous other factors that contribute to mate selection, and any generalization is bound to have exceptions, especially in an animal as complex as the human being. But as generalizations go, financial support is one of the most fundamental.

If women do prefer men of means, then it should follow that decreasing family size in the 70s and 80s was the result of falling individual wages. As shown earlier, earnings have indeed declined. But there is even more direct evidence that financial support brings and keeps two-parent families together. Working from the results of the 1990 Census, Donald Hernandez has irrefutably proven that the financial condition of the family is the best predictor of its future continuation or dissolution. Among white families where the father has a steady income, the dissolution rates are lowest. Among black families, the dissolution rates are lowest when both parents work - which reflects the fact that black men suffer wage discrimination and need the help of a spouse to keep their families afloat. A lack of these financial supports suggested a higher risk of marital failure.7

A University of Michigan study following 5,000 families has found that poor families are twice as likely to divorce as others.8

Researchers at the University of Chicago found that inner city black men are over two and a half times more likely to marry the mothers of their children if they are employed beforehand. And this finding is true of women as well; the greater a woman's earning potential, the more likely she is to marry.9

All this suggests a solution to the break-up of the lower-class family. The best way to promote marriage and two-parent families is to empower individuals economically.

Polarized wealth and income not only inhibit family-formation among the poor -- they have the opposite effect for the rich. Sociobiologists have found that polygamy occurs most frequently in societies of unequal wealth. Only wealthy men take multiple wives; poor men never do. And the point at which a society starts to practice polygamy is the point at which a woman finds more support from a married man than from an unmarried one. Modern laws against polygamy seem strong enough to counter this tendency, but then one must consider polygamy in its modern form: the wealthy man and his mistresses.

The following chart shows the percentage of married men who have affairs in different income brackets:10

Income Bracket      Percent of married men who have affairs
Under $5,000        16% 
5,000 - 10,000      25 
10,000 - 20,000     33 
20,000 - 30,000     45 
30,000 - 40,000     55 
40,000 - 50,000     67 
Over 50,000         70

Some feminists (but not all, I have been reminded!) oppose sociobiology because they feel it reduces mating to a mere exchange of money for sex. Some also feel that it reinforces the stereotype that only men have money and power, while women are valuable only for their sexual contributions. However, feminists who accept the findings of sociobiology point out that family formation may be promoted just as much if both partners are financially solvent; we don't know yet because males dominate the world's economies, and women's equality in this area is just emerging. Also, it is difficult to believe that romance can be reduced to a crude exchange of money for sex. Rather, financial stability more likely serves as a foundation upon which everything else in the relationship is built, including love, friendship, trust, etc.

Others criticize sociobiology because of its many apparent exceptions. I say apparent because with so many factors influencing family-formation, it is sometimes possible for the leading factors to get buried. For example, prior to the industrial revolution, the rich had higher birthrates than the poor. Emperors and tyrants almost universally kept large harems; the more powerful the emperor, the more polygamous he was. But as democracy and industrialization have spread, the birthrate of the rich has generally fallen below that of the poor. (This is not a contradiction of the above chart. It is possible to have a greater percentage of families among rich households; they just have lower birthrates.)

Part of the reason may be that industrial economies are more equal than those based on serfdom, which means that competition for wealth and status is now more widespread, and therefore more difficult. Today it might be a better reproductive strategy to invest heavily in a few children than sparsely in many children. Another possible explanation is that children were economic assets in agricultural societies (that is, they served as farm hands); whereas children in industrial societies are more of an economic burden. And the higher birthrate among the poor might be an artifact of industrialization, which is still rather new to the human experience. Whatever the reason, it proves that there are other factors than just wealth that contribute to high birthrates.

A second objection is that the birthrate of the nation's very poorest is unusually high -- in fact, the nation's highest. There is some argument about why this is so. One theory is that humans respond to dire threats to their existence by bearing more children. For example, after famine struck Somalia, its birthrate climbed to one of the highest in the world. In the United States, hospitals report a spike in the local birthrate nine months after a hurricane or earthquake strikes the region. Teenage mothers - who generally come from the poorest segments of society - say they actually seek their pregnancies because they want to feel the importance that motherhood brings. But this may be the language of survival. Political scientist Andrew Hacker writes: "Many youths reside in such lethal surroundings they cannot be sure how long they will remain alive. Hence the early urge to get the next generation started. While they may not cite this as their reasoning, it is something that Charles Darwin would understand: even in the face of vicissitudes, every species seeks to ensure its own perpetuation." 11

Although these exceptions pose theoretical challenges to sociobiology, there is so much evidence linking prosperity to increased birthrates that few scientists deny the connection. The problem is figuring out exactly how this connection works.

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1 William Chafe, The American Woman: Her Changing Social, Economic, and Political Roles, 1920-1970 (New York: Oxford University Press, 1974), p. 217.
2 U.S. Bureau of the Census, Current Population Reports, P60-184.
3 R.L. Trivers, Social Evolution (Menlo Park: Benjamin/Cummings, 1985), cited in Matt Ridley, The Red Queen: Sex and the Evolution of Human Nature (New York: Penguin Books, 1993), p. 299.
4 Mary Batten, Sexual Strategies: How Females Choose Their Mates (New York: G.P. Putnam's Sons, 1992), p. 26.
5 Personal communication to Batten, p. 62.
6 Personal communication to Batten, p. 63.
7 Donald J. Hernandez, U.S. Bureau of the Census, cited in Sam Robert's Who We Are (New York: Random House, 1994, 1995), p. 51.
8 The University of Michigan Panel Study of Income Dynamics, cited by Stephanie Coontz in The Way We Never Were: American Families and the Nostalgia Trap (New York: HarperCollins, 1992), p. 259.
9 Mark Testa, Nan Marie Astone, Marilyn Krogh, and Kathryn Neckerman, "Employment and Marriage Among Inner-City Fathers," Annals, AAPSS 501 (January 1989): 87, 90-91; Neil Bennett, David Bloom, and Patricia Craig, "Divergence of Black and White Marriage Patterns," American Journal of Sociology 95 (1989), p. 709.
10 Study conducted by American Couples, cited by Les Krantz in America by the Numbers: Facts and Figures From the Weighty to the Way-Out (New York: Houghton Mifflin Company, 1993), p. 4.
11 Andrew Hacker, Two Nations: Black and White, Separate, Hostile, Unequal (New York: Ballantine Books, 1992), p. 84n.