My two are not genetically related but very close in IQ. I posted on a recent thread about how close they are with their scores...both were in the 140's for non-verbal (Perceptual Reasoning) with a lower verbal score (DD did better than DS with verbal ability, however). And both have weaknesses with processing speed. What are the odds of taking two random kids off the street and having both score in the 140's for non-verbal ability, with that being the highest score for both? Probably not very great. I think siblings tend to be close in IQ, but there are other things going on besides genetics which have influenced cognitive development. Both in terms of the strengths and the weaknesses.
I wouldn't call myself dumb, but my brother would probably have a much higher IQ score than me if we were tested. And our abilities are very different. I remember taking the PSAT and was in the national merit program, but it was because of my verbal score. My brother is a high energy physicist and excels most at math and non-verbal ability. The stuff he does is Greek to me (both literally and figuratively). So siblings can be very different. My brother is much brighter than anyone I can think of in the family--comparing him to my parents, grandparents, etc. So if it came from genetics, it's not obvious who had those genes.
