Only children always want to get their way, can’t share and are generally selfish—or so the long-held prejudice goes. According to recent research, however, these claims are overstated. So where did these biases come from?

In A Study of Peculiar and Exceptional Children published in the 19th century by educator E. W. Bohannon from Clark University in Massachusetts, detailed the results of a questionnaire—a new form of data collection at the time—filled out by 200 test subjects. In it he had asked respondents about the peculiarities of any only children they knew. In 196 cases participants described children without siblings as excessively spoiled.

Bohannon’s colleagues agreed with the results and the idea took hold. The widespread skepticism toward only children was further strengthened by the fact middle-class families were having fewer children and society’s privileged class feared growth of the population’s “inferior strata.” Furthermore, in the early 20th century, some were concerned that growing up without siblings causes children to become hypersensitive: If the parents concentrated all their worries and fears on one offspring, that child would become overly sensitive and eventually a hypochondriac with weak nerves.

According to data compiled in the 21st century, however, these notions are nonsense and only children show no serious deficits. Toni Falbo, a psychologist at The University of Texas at Austin, and an only child, opposes the idea you need brothers and sisters to grow into a decent person. In her 1986 survey, for which she examined more than 200 studies on the subject, she concluded the characteristics of children with and without siblings do not differ. The only difference, she found, was that only children seemed to have stronger bonds with their parents compared with children who had siblings.

This idea was later confirmed by a 2018 study in which Andreas Klocke and Sven Stadtmüller from the Frankfurt University of Applied Sciences used longitudinal data from around 10,000 German schoolchildren to track down the peculiarities of firstborns, only children and those with siblings. Among other things, they looked at the quality of the parent–child relationship, a metric measured by how easy it was for a child to speak with their parents about important matters.

Twenty five percent of only children considered their relationship with their parents positive. Just under 24 percent of firstborns, 20 percent of middle children and 18 percent of youngest children also reported very good relationships with their parents.

Despite having strong bonds with their parents, only children often regret having grown up without siblings. In 2001 Lisen Roberts of Western Carolina University and Priscilla Blanton of the University of Tennessee Knoxville asked young adults to look back on their childhoods. Many found it particularly unfortunate they did not have a trusted playmate as those with siblings had. In fact, preschool-aged only children often developed imaginary friends with whom they could be allies and share everyday things. But there’s no reason for concern—creative play with imaginary companions promotes social development and the ability to communicate.

There are, however, indications only children are less willing to come to terms with others. In new findings from China, where the one-child policy dictated family planning for nearly four decades, researchers led by psychologist Jiang Qiu of Southwest University, Chongqing, examined 126 students without siblings and 177 with siblings in terms of thinking ability and personality. In one survey only children achieved lower scores in terms of how tolerant they were. According to the five-factor model (FFM), a model of personality dimensions, particularly tolerant people are altruistic, helpful, compassionate and cooperative. Intolerant individuals are often characterized as quarrelsome, distrustful, egocentric and more competitive.

The students were also asked to master a creativity test known as the Torrance Tests of Creative Thinking (TTCT). For example, they had to come up with as many original uses for an everyday object, such as a tin can. As it turns out, only children seem to be better lateral thinkers, meaning they could solve problems more creatively, especially in the category of flexible thinking. This, the authors explain, could be because without siblings only children often had to rely on themselves and were thus forced to become inventive and resourceful at an early age.

But that is not all. MRI tests revealed differences in brain structure. In the supramarginal gyrus, a cortical area associated with creativity and imagination, researchers found more gray matter (linked to intelligence) among only children. Researchers, however, discovered fewer gray cells in the frontal brain, more precisely in the medial prefrontal cortex (mPFC), of only children than those with siblings. This deficit was accompanied by lower tolerance. Earlier studies also attributed important functions to this brain region when it comes to processing emotional information, including the ability to attribute feelings to others and regulating one's own emotions.

How much influence the effect of being an only child has is questionable. It may depend on how many other opportunities an only child regularly has to develop his or her social and cognitive abilities. After all, only children are by no means cut off from social settings—contacts in kindergarten, for example, offer a varied interpersonal training ground. Parents likely have to work harder at teaching their only kids social skills and engineering opportunities where children would have to share their toys, books and parental attention. Otherwise, creating a loving and calm environment seems more important than the number of children in a household.