Worldwide, the trend toward smaller families is reshaping childhood experiences. A growing number of children are growing up without siblings, a demographic shift prompting researchers to investigate the long-term effects on brain development and behavior.
Until recently, studies yielded inconsistent results. Some suggested that only children exhibited enhanced social skills and academic performance, while others indicated a higher incidence of behavioral problems. Now, a novel study published in Nature Human Behaviour, conducted by researchers at Tianjin Medical University General Hospital and collaborating institutions in China, offers a more nuanced understanding of how growing up without siblings impacts the adult brain.
“With the global increase in single-child families, the effects of growing up without siblings (GWS) on the adult brain, behavior and the underlying mechanisms,” wrote Jie Tang, Jing Zhang, and their colleagues. The research team analyzed data from the CHIMGEN cohort, comparing 2397 carefully matched pairs – one only child and one individual with siblings – examining brain structure, brain function, cognitive abilities, personality traits, and mental health.
The study revealed distinct patterns in the brains and behaviors of only children. Researchers observed higher integrity of language-related brain fibers, but lower integrity in motor fibers. Only children also exhibited larger cerebellum volumes, smaller cerebral volumes, and reduced spontaneous brain activity in the frontotemporal regions. Simultaneously, the study found positive correlations between being an only child and cognitive performance, as well as mental well-being.
Importantly, the researchers found that many of these effects weren’t directly caused by the absence of siblings, but rather by environmental factors. Socioeconomic status, maternal care, and familial support played a significant role in shaping brain development and behavioral outcomes. This suggests that interventions aimed at enriching the experiences and opportunities available to only children could positively influence their brain development, mental health, and overall behavior.
The findings challenge the common stereotype of the “spoiled only child.” The study indicates that the brains and behaviors of only children are complex and heavily influenced by their upbringing, presenting opportunities to positively guide their development.
