The parents genes are only 120 because 10 points were based on environmental "luck". Genetically they had the genes for 110 IQ +/- 10 points to accommodate the

The parents genes are only 120 because 10 points were based on environmental "luck". Genetically they had the genes for 110 IQ +/- 10 points to accommodate the environmental luck. The two kids had average luck, so they got 110 IQ, but they still have the same genes. So when they have kids with others with the 110 IQ gene's, they will still be 110 +/- 10. A simpler explanation: you might be the child of geniuses but they dropped you on your head repeatedly as a baby. You might not be so smart as an adult because of it but your kids will have genius genes, not dropped on head genes.