A new study has suggested that birth order within families, long blamed for sibling rivalries, may also affect children's personality and intelligence.
Researchers say that first-borns are typically smarter, while younger siblings get better grades and are more outgoing.
In the study, lead author Tiffany L. Frank, a doctoral candidate at Adelphi University in Long Island, N.Y. and her colleagues surveyed 90 pairs of siblings in high school.
Subjects were asked to report their grades and rank themselves as compared with their siblings on intelligence, work ethic and academic performance.
The researchers also obtained academic tests scores and grades to verify the students' own reports, reports Live Science.
First-borns received higher tests scores, in math and verbal ability, while later born children had better grade point averages in English and math.
In a second experiment researchers looked at differences in personality between 76 pairs of siblings in high school. Subjects rated themselves on a series of statements designed to assess personality.
Later born siblings were found to be more extroverted (sociable, outgoing), sentimental, forgiving and open to new experiences than their older siblings.
First-borns were found to be more perfectionistic than their younger siblings.
First-borns might score higher on measures of intelligence, because, at some point in their lives, they were only children who were the sole recipients of their parents' attention.
Younger siblings might earn better grades, because they received mentoring from first-borns who already had to tackle certain subjects, the researchers say.
Also, later born children might feel extra pressure to be competitive, and might try to out-do their older siblings in the hopes of gaining extra attention from parents.
The youngsters might also be more open to new experiences, because they "see the obstacles that their older siblings have overcome and therefore feel more secure in challenging themselves," the researchers say.
The findings were presented at the 118th Annual Convention of the American Psychological Association.