Who is "really, really smart?" Boys or girls?

A new study found that young U.S. girls are less likely than boys to believe their own gender is the most brilliant.

While all 5-year-olds tended to believe that members of their own gender were geniuses, by age 6 that preference had diminished for girls — a difference the researchers attributed to the influence of gender stereotypes.

SEE ALSO: 7 strategies for raising confident girls in the Trump era

"We found it surprising, and also very heartbreaking, that even kids at such a young age have learned these stereotypes," said Lin Bian, the study's co-author and a doctoral candidate at the University of Illinois at Urbana-Champaign.

A girl looks through a microscope during the 2016 Russian Festival of Science in Moscow. More

Image: Vladimir Trefilov/Sputnik via AP

"It's possible that in the long run, the stereotypes will push young women away from the jobs that are perceived as requiring brilliance, like being a scientist or an engineer," she told Mashable.

A growing field

The study, published Thursday in the journal Science, builds on a growing body of research that suggests gender stereotypes can shape children's interest and career ambitions at a young age.

A global study by the Organization for Economic Cooperation and Development found that girls "lack self-confidence" in their ability to solve math and science problems and thus score worse than they would otherwise, which discourages them from pursuing science, engineering, technology and mathematics (STEM) fields.

A 2016 study suggested a "masculine culture" in computer science and engineering makes girls feel like they don't belong.

Students work on a Youth Media project at a STEM-focused public school in Astoria, New York. More

Image: AP Photo/The Christian Science Monitor, Ann Hermes

Thursday's research looks not at specific skills but at the broader concept of high-level intellectual abilities. In short, can girls be geniuses, too?

Sapna Cheryan, a psychology professor at the University of Washington who was not involved in the study, said the results were "super important" because they're among the first to show us how young children — not adults or high-schoolers — respond to gender stereotypes.

But she said the findings are just as revealing for young boys as for girls.

"It's not that girls are underestimating their own gender — it's that boys are overestimating themselves," she told Mashable. Cheryan was the lead author of last year's masculine culture study.