Average IQ Score Determined by Birth Order?

According to a recent study of nearly 250,000 males between 18 and 19 years old, the first-born had an average IQ score 2.3 points higher than their younger siblings. Doesn't sound like much, right? But, those 2.3 points increase a child's chances of getting into an Ivy League school by 30 percent. The results also proved that IQ is, at least in part, determined by social birth order and not by genetics, putting an end to a nearly 70 year old debate.

But, don't start resenting your older brother just yet. While the 2.3 points are fairly significant, they only reflect the educational potential of an individual. So, even if you weren't the first to arrive on the scene in your family, you are still entirely capable of being more successful than all of your siblings combined. It's all about how you use what you've got.

There are several theories as to why first-born children usually have higher IQ's. One, they are usually given undivided attention during their early developmental years. As additional children are born, the attention of the parents is spread more thinly across the entire family.

Another possible explanation, parents usually spend more money on the oldest sibling, simply because that child is the first one to require the extra expenses. For example, the oldest child would most likely be the first to want to take a class of some kind, get involved in sports, go to college, etc.

The theory that one of the researchers thinks is most accurate is called "niche partitioning". Basically, the oldest child is given the most authority and responsibility, therefore the parents tend to see him as a surrogate parent to the younger siblings. This higher ranking then drives the later-born children to find their "niche" in the family.

Because older children already occupy the "disciplined and wise" niche, younger children have to find other roles to play. "So, younger siblings look for other things to be good at," said Frank J. Sulloway, a visiting scholar at the University of California, Berkeley, Institute of Personality and Social Research. "It may be that that extra 2.3 points in IQ reflects an investment of time to get that, and the later-born is investing that time in something else and is getting 2.3 extra points in something else," he added.

Given that each child is finding his or her own niche, the difference in IQ is nothing for parents to worry about, Sulloway said.

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