They’ve been called spoiled, narcissistic, asocial and maladjusted. They’re said to be attention-seeking perfectionists who can’t tolerate disorder or crowds. And they’re infiltrating the country like an invasive species, exhorting others to help swell their ranks.

They’re America’s only children, and there are more of them than ever: adored centerpieces of nearly a quarter of the nation’s families. They are the most stereotyped of children, and the fastest-growing segment of birth order, poised to change the social landscape of a nation forged by large families. If, as lore has it, stereotypes are grounded in truth, the rise of the singleton — selfies, alone — raises an ominous question: Will America be the first modern nation laid low by excessive self-esteem?

It’s a question worth pondering as the only child’s slice of the demographic pie continues to grow. But sociologists and psychologists say a preponderance of only children might slightly increase the nation’s intelligence and productivity, countering negative effects that might include obesity and divorce.

In fact, the advance of only children could raise the collective IQ in the United States two or three points, said Dr. Frank Sulloway, who teaches psychology at the University of California at Berkeley and whose book “Born to Rebel” examines how birth order and family structure have influenced societal change.

The number of households with just one child is climbing in the U.S. and parts of Europe. According to census data, 23 percent of American families have one child. That number increases as a city’s population does; in New York City, the number now tops 30 percent. Not since the Great Depression has the country had so many only children.

But in the 1930s, 64 percent of Americans told pollsters they wanted three children or more. Today, most people tell Gallup 2.5 children is ideal, and that number is under assault by people advocating a de facto one-child policy like China has — not in law, but in practice.

Among the one-child cheerleaders are Brandeis University professor Linda R. Hirshman, who urged women to have only one child to protect their earning power in her book “Get to Work,” and author Bill McKibben, who argued that large families are environmentally reckless in “Maybe One: The Case for Smaller Families.”

To those, add a growing library extolling the single-child life, such as “One and Only” by Lauren Sandler. Sandler challenges the stereotypes of only children as self-absorbed malcontents and maintains that singletons are more mature, cultured and intelligent than children raised amid the inherent competition of siblings. Of course, raising one child is significantly less expensive than four. (The most recent cost bandied by the Agriculture Department is $245,300 to rear a child to the age of 18.) And a much-trumpeted study found that the overall happiness of parents declines with the birth of each child. This may be why Pew Research reports the average American woman today will have 1.9 children, down from 3.7 a half-century ago.

The statistics portend a dramatic foundational reshaping, contributing to what demographer Joel Kotkin calls the “post-familial” age. They explain why Sandler, in her book, considers the “relative incompatibility of motherhood and modernity” and urges Americans to consider “the larger societal costs of having more than one.”

But the effects of birth order on children, while controversial, have been widely studied since Austrian psychiatrist Alfred Adler proposed a connection in the early 1900s, and they pose another question: What are the societal costs of having only one?

‘Two hundred’ percent of attention

In her book “The Death of the Grown-Up,” Diana West skewered what she sees as a growing cultural pubescence, and urged American adults to abandon their quest for eternal youth and embrace a dignified adulthood. A century earlier, Adler (himself the second born of six), posited that only children are more mature than children with siblings since they grow up in the company of adults and as such, enjoy “200 percent” of the adults’ attention.

Could a bountiful crop of only children inject widespread gravitas into the culture? Alas, West says, probably not.

“Because of the tremendous focus on an only child, only children can be raised in an environment of instant gratification, but then so can five siblings,” said West, the mother of adult twins.

Also, the effects of birth order can be mitigated by the spacing of children, and by a child’s perception of his role in the family, said Dr. Marina Bluvshtein of the Adler Graduate School in Minneapolis. For example, if there is seven years’ distance between two children, one or both may be “only” children psychologically. When psychologists at Adler talk about birth order, then, they consider whether it is ordinal (chronological) or psychological, she said.

“The most common themes for psychologically only children, as we can see in literature and I see in clinical practice, are higher need for achievement and lower need for affiliation, problematic peer socialization skills, higher anxiety, and lower agreeableness, among other traits,” Bluvshtein said. Other traits can be positive, such as an exceptional vocabulary, she added.

While some studies have shown that characteristics of only childhood lessen in adolescence and adulthood, one in particular will not abate, Bluvshtein said. That is the anxiety of being the sole caregiver for aging parents, a job consuming more time and resources than ever, in light of America’s lengthening life span. (Of course, the average life span could start to go down in a nation of only children, given that they are 50 percent more likely to be obese than children with siblings, according to one European study.)

Kotkin, troubled by the prospect of the post-familial society (a phrase that he coined), predicts an increasing number of Americans will only have connections with other people online. It’s difficult to see how this trend won’t continue and expand, he says, as more children grow up without siblings and cousins. Famously adept at entertaining themselves, some only children find face-to-face interaction tortuous, and they will be comfortable living alone, like 27 percent of the population already does.

The loner, once an outlier, is becoming mainstream.

Parties of one

Sulloway, of the University of California at Berkeley, has done extensive research on birth order, even examining its effects on 700 professional baseball players who have siblings. He found that younger siblings are more likely to steal bases and be hit by pitches, affirming the conventional wisdom that younger siblings are more likely to be risk-takers.

But only children defy easy classification, he said, as they are prone to exhibit characteristics of children with siblings. They can, for example, possess the conscientiousness and leadership abilities of a firstborn, with the relaxed disposition of the youngest.

But only children from intact families do score two to three points higher on IQ tests, he said, so there might be a slight, but measurable, increase in intelligence.

Anecdotally, the case for an altered America is stronger, particularly if families are wealthier when they have one child, and the child is exposed to a higher standard of living, enjoying trips and lessons that might not be affordable in a family of Waltons or Weasleys. In this scenario, only children might enter adulthood more learned and self-assured.

But they might be deficient in skills that large families teach, such as how to negotiate for the last Oreo, how to concentrate in the midst of noise and disorder and how to share.

“I don’t always handle chaos well,” admits Beth Salamon, an only child who grew up to be communications director of the Rutgers University School of Social Work. “At big parties and family events, I’m the one who slips upstairs and is reading. I’ve also had to learn to have a tougher skin, since I didn’t have the give-and-take at home, the teasing that kids do to one another.”

When she was in kindergarten and was asked to draw a picture of her family, Salamon invented a brother. Now 46, she has two girls and is glad she married a man with two brothers so she and her daughters have a large extended family. That she married a man with siblings is also good, because only children who marry other only children have the highest divorce rate of any birth-order matchup, according to a study last year from Ohio State University.

Even if only children buck the odds and stay married, their family units will be sharply different from those of the past, deficient as they are of cousins, aunts and uncles, the extended family that siblings provide.

“The whole family network will become more attenuated and smaller,” Kotkin said. “When you take that away, people’s identity will be nothing but individuals and the government. There will be no family you can rely on to help you.”

Of course, only children who, like Salamon, regret that they don’t have siblings, may have multiple children and provide some slight buffer to the trend toward smaller families. But they’ll be an exception, Sulloway said. People from large families tend to have large families, and only children tend to have one or two children, he said.

“We are still undergoing the demographic transition toward fewer children that began in the late 18th century, and we see these trends all over the world,” he said. “The rate of only children will go up. It won’t ebb and flow.”

Jennifer Graham is a journalist and author on the East Coast. She can be reached at or on Twitter, @grahamtoday.

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