Gifted Issues Discussion homepage Forums Parenting and Advocacy Are siblings usually gifted also?

Brothers and sisters are usually within five or ten points in measured ability. Parents' IQ scores are often within 10 points of their children's; even grandparents' IQ scores may be within 10 points of their grandchildren's. We studied 148 sets of siblings and found that over 1/3 were within five points of each other, over 3/5 were within 10 points, and nearly 3/4 were within 13 points. When one child in the family is identified as gifted, the chances are great that all members of the family are gifted.

It is reasonable to expect that genetic influences on traits like IQ should become less important as one gains experiences with age. Surprisingly, the opposite occurs. Heritability measures in infancy are as low as 20%, around 40% in middle childhood, and as high as 80% in adulthood.

Shared family effects also seem to disappear by adulthood. Adoption studies show that, after adolescence, adopted siblings are no more similar in IQ than strangers (IQ correlation near zero), while full siblings show an IQ correlation of 0.6. Twin studies reinforce this pattern: monozygotic (identical) twins raised separately are highly similar in IQ (0.86), more so than dizygotic (fraternal) twins raised together (0.6) and much more than adopted siblings (~0.0).