According to a new study, the birth order can modestly affect the IQ score, favoring the first born.
The study, published in the Journal of Science, showed a difference of only two points between IQ scores among two brothers, born at a difference of several years.
The researchers included nearly 244,000 male adolescents from Norway. They, between the ages of 18 and 19, took part in an intelligence test during the medical examination for the army.
Following the test, it was found that those adolescents who were born first in a family with at least two siblings had a higher score than their younger siblings. Also, the score was higher in the case of families with three brothers, where the score of the second born was higher than the last born.
But the strict order of birth was not the only important factor.
The biological order of birth (which includes all children in the family, including those who have died) and the social order of birth (which includes all healthy children in the family) could be just as important in terms of IQ scores.
The same results were maintained when the researchers took into account other factors such as parents' education, mother's age at birth and baby weight.
However, there was another study that showed that before the age of 12, children tend to pass IQ tests of older siblings.
This is possible because younger siblings are less linguistically and cognitively mature, which affects the intellectual environment of the first born, and older siblings live in the environment of younger siblings.
Sometimes the roles of the brothers are reversed, probably because older brothers receive that information explosion from their younger brothers.
For the moment, for the researchers this study remains a real challenge in investigating several directions and reaching other discoveries.
March 20, 2008