Maybe One: An Environmental and Personal Argument for Single-Child Families.

Overpopulation is not high on the list of problems Americans worry about. After all, the birth rate in the United States currently stands below replacement levels, and current demographic predictions, both here and in Europe, suggest that small families are here to stay. Even in third-world countries, the birth rate is declining.

Still, Bill McKibben is worried. We face a population crisis, he tells us, because Americans are living longer. Despite low birth rates, the population is likely to reach 400 million by 2020, nearly double its current size. This natural increase in population means that Americans will face a host of problems ranging from car-clogged highways to the collapse of the Social Security system. How do we prevent this demographic disaster? McKibben's solution is to call for a little procreative thrift: Give up the two-child-family. Stop after one.

This is hardly a new idea. Thirty years ago, Paul Ehrlich's best-selling book, The Population Bomb, called upon Americans to limit family size and to wage a campaign against big families. But the campaign never got off the ground, partly because fertility was already declining among Baby Boomers. A decade later, noting a rapid and unanticipated decline in the birth rate, Ehrlich proclaimed the population trend in the United States a "success story."

What is new and provocative is McKibben's rationale for only one-child families. These families would not only be good for the environment; they would also be good for children themselves. The advantage of siblings is vastly exaggerated, according to McKibben. Citing research studies on only children, he argues that they are likely to do better in school, have more friendships, display more flexibility in gender roles, show more interest in science, math, and literature, and have higher self-esteem than kids burdened with siblings.

McKibben is persuasive, in part because he is that rare thing: a passionate environmentalist and an eminently reasonable man. He is deeply concerned about the damages and depredations caused by too many people on too little land. At the same time, he resists the temptation to call for coercive government measures or even mild social pressures to limit population. (He does advocate reducing the quotas on immigration, however.) Rather, his argument for the one-child family is an appeal to individual conscience and voluntary action. He asks men and women to think and talk about overpopulation in the most personal terms "as a matter of how many children you or I may bear."

McKibben is also persuasive because he practices what he so fervently preaches. The father of a four-year-old daughter, he derides to get a vasectomy. Though he acts on his principles, he confesses very human misgivings. One of the best parts of the book deals with his account of his unexpected bout of post-op tristesse. "There's no set of statistics to explain. . . why it felt odd, why it felt a little shameful, why it felt sad," he writes. Perhaps most impressive of all, McKibben does not try to claim moral-courage points for ending his own reproductive life.

Still his argument for the one-child family population solution is ultimately unconvincing. To begin with, he fails to contend seriously with a competing and well-supported scenario of population implosion. In a recent article in The Public Interest, Nicholas Eberstadt painstakingly documents a pattern of worldwide fertility decline and paints a futuristic portrait of a graying world population with over 55 percent of the world's women past reproductive age. Over a couple generations, he says, the impact of sustained low fertility could change the composition of the family itself. Children would grow up with parents and grandparents but would have no siblings, cousins, aunts, or uncles. Such a transformation of the family would surely have a profound impact on our sense of social solidarity, obligation, and future orientation, Eberstadt observes. And in America, the most individualistic nation in the world, this demographic trend could dramatically accelerate social atomization.

Too, McKibben's sweeping case against siblings is biased and distorted. He relies heavily upon a single study based on small clinical samples of individuals in therapy where sibling incest, aggression, and conflict figure far more prominently than they do in the general population. And he salts the clinical findings with evidence from sitcoms and his own anecdotes of fights with his brother. Given this highly selective reading of the evidence, it is not surprising that siblings fare so poorly.

But the chief problem with McKibben's argument is that it treats children as if they were costly consumer items on a par with cars. In his environmental calculus, there is very little difference between formula-guzzlers and gas-guzzlers. This devaluation of children also contributes to a devaluation of childrearing as an adult vocation. McKibben believes that there are better uses for adult energies and resources than raising a bunch of children. By limiting his own family to one, he is able to do other things: work on Adirondack conservation issues, belly-dance, and teach Sunday school. Indeed, he claims that having fewer children will free parents to make the world a better place. But there is no evidence to support the idea that parents with one child are more altruistic than parents with two or more. Nor is there evidence to suggest that limiting family size will reduce family consumption. McKibben's own exemplary conduct notwithstanding, I fear that a nation of Cleavers without Beaver may become a nation where June and Ward buy bigger houses and cars and dedicate themselves to doing their own thing.

Barbara Dafoe Whitehead's most recent book is The Divorce Culture (Knopf).