We know from IQ tests in children that cognitive ability can be determined early; even in infants, simple tests of mental development (like pulling a string to ring a bell, matching pictures, and sorting pegs by color) can predict mental ability later in life. So, if it’s possible to gauge mental ability of 7-year olds, and if fraternal twins typically score differently on IQ tests, why did the kids in the study [fraternal twins] perform at the same level? What was special about these 7-year olds?3QD
The answer, of course, was poverty. When researchers compared the IQs of 7-year olds from affluent backgrounds, variation between twins was huge- as expected. Poverty effectively erased an individual’s genetic contribution towards intelligence; thus, twins from low socioeconomic standing bunched together on the IQ spectrum, and twins from high socioeconomic standing fanned out according to their innate genetic potentials.