It's time to end the sibling rivalry once and for all: a new study suggests first-born children are generally smarter than their younger siblings, and parents are to blame.

Indeed, children who were born first are not much more intelligent because of genetics, but because of the advantages they get from parents — something that younger siblings are not lucky enough to receive, the study said.

Parental Support

Researchers from the University of Edinburgh examined data involving 5,000 children who took picture vocabulary and reading tests every two years from age one to age 14. They considered several factors such as the family's economic conditions and background.

First-born children scored higher in IQ tests than their younger siblings at age one. They also had higher scores on tests that involved matching letters, reading, names, reading single words aloud, and picture vocabulary.

Although kids received the same amount of emotional support from parents, regardless of birth order, parents appeared to spend less time on brain-simulating activities with their younger children. They took less part in activities such as reading with their younger children, doing crafts, or playing musical instruments compared to the first-born.

All these contribute to improved thinking skills among first-borns compared to their younger siblings, the study said.

"Our results suggest that broad shifts in parental behavior are a plausible explanation for the observed birth order differences in education and labor market outcomes," said study author Ana Nuevo-Chiquero.

Limitations Of The Study

The results are interesting, but researchers emphasized that these findings are more of a generalization and will not apply to every family. Past studies have shown that the link between birth order and intelligence may be highly overrated, according to Medical Daily.

For instance, a 2015 report examined the intelligence and personality of 377,000 high school students — the largest study ever that focused on outcomes of birth order.

Researchers found that the birth order was insignificant. Although first-borns tended to be smarter than younger siblings, this was only by one point. First-borns tended to be more agreeable, extroverted, conscientious, and have less anxiety than younger siblings, but the difference was extremely small.

There's also bad news for first-borns: another 2015 study found that first-borns were up to 20 percent more likely to become short-sighted compared to their younger siblings.

They were also more likely to become overweight, as a study of middle-aged men found that first-born children were likely to weigh 14 pounds more than second-born siblings. However, the trend doesn't mean that first-borns are destined for obesity, the study said.