A new study confirms a longstanding belief about birth order: On average, the oldest sibling will have the highest IQ.
The study, published in the Proceeding of the National Academy of Sciences, found that older siblings score, on average, 1.5 points higher on intelligence tests than second-born kids. In families with more than two children, each successive child’s score drops another 1.5 points.
STORY: Is Birth Order Meaningless?
The Leipzig University researchers who conducted the study found that intelligence was the only characteristic even mildly determined by birth order — extraversion, emotional stability, agreeableness, conscientiousness, and imagination were all found to be unaffected by where a person falls in the family tree. “Several psychologists suggested that the position among siblings might be one important environmental determinant of personality development,” study author Stefan Schmukle, a professor of psychology at the University of Leipzig, tells Yahoo Parenting. “Our results suggest, however, that the development of personality might be less determined by the role within the family of origin than previously thought.”
Why, then, would intelligence be dependent on birth order? “For me, the most convincing hypothesis is that the parents’ attention is greater and intellectual stimulation is higher if there is only one child,” Schmukle says.
Rodica Damian, a professor of psychology at the University of Houston who has studied birth order and was a reviewer on the new study, agrees with this hypothesis. “First-borns get stimulated more, especially verbally, because, maybe, the parents have more time for them,” Damian tells Yahoo Parenting. “The more siblings in the family, the more the intellectual environment gets diluted. As a first-born, you only talk to adults — they have a large vocabulary, they talk about more high-level ideas. When there are five children, most of your time as a child will be spent talking to other children, who have less intellectual ideas to share. Instead of learning words from your parents, you are learning words from your brothers or sisters.”
But Damian points out that while this difference in IQ is significant across a giant test sample — like the 20,000 people analyzed in this German study — in any given family, it’s a tiny difference. “If the same person took an intelligence test twice, their score would probably come out different by more than one point,” she says. “If you are talking to two people with a range of 1.5 IQ points, you won’t notice the difference just in conversation.”
And though these study results are on average, there are plenty of sibling sets who don’t follow this intelligence pattern. “There are a lot of families where the second-born child is significantly smarter than the first-born,” Damian says. “Younger kids shouldn’t blame all their intelligence differences on birth order, and parents should certainly not expect less of their younger children.”
These findings should simply serve as a reminder to parents that each child needs equal attention. “If you want to equal out that one-point difference, make sure you read all of your kids the same amount of stories and talk to them the same amount,” Damian says. “But at the same time, don’t feel guilty if you can’t always do everything equally. If it happens that one kid has a big difference in intelligence, a lot of that might just be random.”
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