EDINBURGH, Scotland — First-born children often think they’re smarter than their siblings – and now science seems to back them up.

A recent study conducted jointly by researchers at the University of Edinburgh in Scotland and the University of Sydney in Australia found that eldest children tended to have higher IQs than their younger brothers and sisters, performed better in school, and even earned more income.

The reason isn’t because first-born children receive greater emotional support at home, the researchers found. Rather it’s because their parents pay special attention to developing their thinking skills, while latter-born children receive comparatively less encouragement in this area.

“Our results suggests that broad shifts in parental behavior are a plausible explanation for the observed birth order differences in education and labor market outcomes,” Dr. Ana Nuevo-Chiquero, one of the study’s authors and a lecturer the University of Edinburgh’s School of Economics, said in a release.

The researchers arrived at their conclusion by examining longitudinal data collected by the U.S, Bureau of Labor Statistics on 5,000 children as they matured from early childhood. They matched that information with additional survey data on the attitudes and behaviors adopted by parents beginning with the pre-birth period of their children through early adolescence.

Parents were more likely to engage in mental stimulation activities such as reading to their children or playing musical instruments in the case of their first-born, researchers found. Mothers were also more likely to smoke and drink during their pregnancies in the case of the latter-born, possibly weakening those children’s mental development.

According to the study, the mental development “gap” among first- and latter-born children starts early — and never narrows. By age one, first-born children are achieving scores on cognitive assessment tests that surpass those of their siblings and their performance edge grows prior to their entrance into primary school.

The persistence of that advantage for so long accounts for the higher educational and career attainment levels for first-born children, researchers concluded.

The study, based on broad statistical associations, cannot explain the anomalies in development one might find in individual families. In addition, it is unknown whether the mental gap has been growing or shrinking over time

Earlier studies, including one conducted in 2010 among paired siblings in New York City, also found that first-born children displayed higher IQs. However, researchers in that study also found that younger siblings worked harder in school and ended up achieving better grades — which could boost their career prospects.

If so, family pecking order may not be destiny after all.