Eldest children are smarter than younger siblings - Study

Taking the debate one step further over relationship between birth order and intelligence, Norwegian researchers have determined that the eldest child in a family tends to develop higher IQ (intelligence quotient) than his sibling, contending the reason is not genetics but the way children are treated by their parents.

In their study that published Friday in the U.S. journal Science, the researchers have found that the firstborn children are smarter than their younger brothers, and this is not due to the biological factors like prenatal environment, but the way they're raised in the family.

Children raised as the eldest showed slightly higher IQs than their younger siblings, researchers said. This finding held true even in those cases where sons became the eldest in the family after the death of an older sibling, their IQ level was higher by an average of 2.3 points than their younger brothers, Norwegian researchers conclude in their study.

To reach their conclusion, Dr. Petter Kristensen, an epidemiologist at the University of Oslo and the lead author of the Science study along with his fellow researcher Tor Bjerkedal, of the Institute of Epidemiology, Norwegian Armed Forces Medical Services, studied two sets of data.

The first set involved the military records of more than 241,300 men born between 1967 and 1976 and the other compared the scores on intelligence tests of 63,951 pairs of brothers. They included men born first, second, or third who had not experienced the early loss of an older sibling for comparison in their study.

After analyzing data on birth order, health status and I.Q. scores, Kristensen and Bjerkedal found that older brothers had IQ's averaging just over 103, which was 3 percent higher than those for second-born sons and 4 percent higher than those born third.

Both the scientists then examined I.Q. scores in 63,951 pairs of brothers, and found the same intelligence level. This means the association between IQ and birth order is related to the social rank instead of the actual birth rank.

"We provide evidence that suggests quite strongly that this effect is not an artifact, and that it is not linked to gestational factors -- adverse pregnancy effects," Kristensen said.

"Indirectly, it supports the theory that social support and attention within the family explain the difference. First children will not have to share this attention at first. The more children, the less attention will be provided to each child if parental resources are limited," he added.

Scientists have long been arguing about the relationship between IQ and birth order. Researchers hope their large study could settle more than a half-century old scientific debate over the issue.

Calling the Science findings, "a dream come true," Frank J. Sulloway, a psychologist at the Institute of Personality and Social Research at the University of California in Berkeley who wrote an editorial to accompany the article, said, "This study really puts to an end a debate that's been going on for more than 70 years," adding that "The theory of biological differences is pretty much dead as a doornail."

Different opinions are presented by the researchers in different studies for the development of IQ levels in children.

In February, researchers at the National Institutes of Health, the University of Bristol in Britain, and the University of Illinois-Chicago presented their study, saying seafood is a key source of omega-3 fatty acids, which is super beneficial for fetal brain development.

Eating fish during pregnancy could help expecting mothers improve their children’s early development and IQs, a joint British and American study says, revealed the joint British and American study that was published on February 15 issue of the British journal Lancet.

Another study, conducted last year in December by a team from Southampton University, links higher IQ to being vegetarian. In their study, the researcher found those who were vegetarian by 30 had recorded five IQ points more on average at the age of 10.

A normal brain grows at an amazing rate during development and at times 250,000 neurons are added every minute. It’s also believed that by the age of 2 years the brain is 80% the size of the adult brain.