Is One Kid Enough?

Why do people keep having kids? After all, children cost their parents more in food and college tuition than they bring in by, say, working the family farm. And in developed countries where parents feel the financial pinch, birthrates have dropped accordingly.

Conventional wisdom dictates that people become parents because children bring joy. But do they really? For scientists studying the subject, simply correlating parenthood and happiness can't answer this question, since happy people might be more likely to have kids to begin with. But a study that compared happiness levels in adult identical twins—some of whom are parents and some who aren't—may be getting to the bottom of the issue.

The study, headed by sociology professor Hans-Peter Kohler of the University of Pennsylvania, found that people with children are, in fact, happier than those without children. But such happiness gains differ for mothers and fathers.

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In comparing identical twins, Kohler found that mothers with one child are about 20 percent happier than their childless counterparts; and while fathers' happiness gains are smaller, men enjoy an almost 75 percent larger happiness boost from a firstborn son than from a firstborn daughter. The first child's sex doesn't matter to mothers, perhaps because women are better than men at enjoying the company of both girls and boys, Kohler speculates.

Interestingly, second and third children don't add to parents' happiness at all. In fact, these additional children seem to make mothers less happy than mothers with only one child—though still happier than women with no children.

"If you want to maximize your subjective well-being, you should stop at one child," concludes Kohler, adding that people probably have additional children either for the benefit of the firstborn or because they reason that if the first child made them happy, the second one will, too.

Kohler adds that most previous research has asked how specific factors—such as marriage or childbirth—contribute to happiness. His study, in contrast, asks a general question about parenting and happiness.

What seems to happen over time, says Kohler, is "you look forward to having a child, then you have it and find it really difficult and your happiness dips, and then you see a substantial gain." Overall, he says the lesson from the study is that "just having reproduced at least once seems to be the crucial aspect of providing the happiness gain."

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