Maternal effects, often assumed to be negligible, account for 20% of covariance between twins and 5% between siblings, and the effects of genes are correspondingly reduced, with two measures of heritability being less than 50%.
In the case of the inheritance of IQ or a certain degree of giftedness, the relatives of probands with a high IQ exhibit a comparably high IQ with a much higher probability than the general population. Bouchard and McGue (1981) have reviewed such correlations reported in 111 original studies in the United States. The mean correlation of IQ scores between monozygotic twins was 0.86, between siblings, 0.47, between half-siblings, 0.31, and between cousins, 0.15. From such data the heritability of IQ has been estimated at anywhere between 0.40 and 0.80 in the United States. The reason for this wide margin appears to be that the heritability of IQ rises through childhood and adolescence, peaking at 0.68 and 0.78 in adults, leaving the overwhelming majority of IQ differences between individuals to be explained genetically.
« Older Oil sands will pollute Great Lakes... | Paavo Haavikko, one of Finland... Newer »
This thread has been archived and is closed to new comments
Buy a Shirt