Intelligence is a measure of innate cognitive or thinking ability. The results of a wide range of tests of higher order thinking processes are strongly correlated suggesting an underlying factor, g, that is related to the mental manipulation of images, symbols, words and numbers. Twin studies indicate that approximately 60 percent of g is due to genes alone, 22 percent to the environment and 18 percent to a gene-environment interaction. Some studies show a genetic component to IQ as high as 87 percent. IQ is positively correlated with virtually every prosocial aspect of civilized man. [p478]
The genetics of reason
To what extent are genetic factors involved in the ability to carry out rational thought? [p473]
