Source: James Thompson posting on Unz.com, Jan 2017
Only 4% of the white population can do all the tasks in the list. 21% get to the 4th level but cannot do carpet cost type problems, and at the very bottom 14% have very simple skills, which do not include locating an intersection on a street map. For many of you reading this, the finding will seem incredible. It is incredible. Human differences are hard to believe, but they are matters to be demonstrated, beliefs notwithstanding.
In a large Dutch twin study (Posthuma et al ., 2003b ),the same identical twins were given mental test batteries repeatedly over time to assess general intelligence. The heritability estimate of general intelligence was 26% at age 5, 39% at age 7, 54% at age 10, 64% at age 12, and starting at age18 the estimate grew to over 80%. The increases could be due to several factors including more genes “turning on” with increasing age or gene– environment interactions.
in a study of 641 Brazilian school children, SES did not predict scholastic achievement, but intelligence test scores did (Colom & Flores-Mendoza, 2007). An even larger classic study had data on 155,191 students from 41 American colleges and universities. Their analyses showed that SAT scores predicted academic performance about the same even after SES was controlled; that is, SES added no additional predictive power (Sackett et al ., 2009 )
In 1988 Haier published the first PET study of students taking the Raven’s Matices test, showing that the brains of such students differed in terms of areas activated from those students doing a simpler attention task. In a master-stroke he correlated the Raven’s scores with brain activity, showing that the brightest students showed less brain activity. That’s right: less activity. Hence my frequent advice to earnest people who want to use more of their brain, which is that they should be bright enough to use less of their brain. Why sweat the small stuff?
Haier and colleagues proposed the brain efficiency hypothesis of intelligence:higher intelligence requires less brainwork.