Genes and IntelligenceRelative Influence of Inherited and

Environmental Factors Upon Behavior

Genes and Intelligence: Biological Perspective

Twin Studies:› Intelligence scores of identical twins raised together

are virtually the same (as if the same person took the IQ test twice)

› Fraternal twins had less similar scores than identical twins

› Identical twins raised separately and identical twins raised together but treated differently also have very similar IQ scores

› Brain scans have shown that identical twins have very similar grey matter volume and are virtually the same in areas of verbal and spatial intelligence

Researchers have also compared families with adopted children and families with biological children

In childhood, the IQ scores of adopted children correlate “modestly” with that of their adopted parents

However, over time, the similarities between adopted children and their parents become less and less while similarity with their biological parents increase

This suggests that genetic influence increases over the life span while environmental influence decreases

Intelligence: Environmental Factors

There is evidence to suggest that environment also has an effect on intelligence.

With regard to genetic make-up, fraternal twins are no more alike than non-twin siblings

However they score more similarly on IQ tests than non-twin siblings

Researchers believe this is because they are treated more the same since they are of the same age

Researchers have done a number of studies in order to determine the effects of environment on intelligence

When studying children who have been moved from orphanages to more stimulating environments, their IQ tends to increase.

This suggests that when children are given more love and attention in a stimulating family environment, their IQ scores will increase

Race and Intelligence

Numerous studies have shown that African-Americans tend to score 15 pts lower on IQ tests. WHY?

In the first half of the 20th C, some researchers held the controversial view that this was due to genetics.

However, the last 30 yrs of research on IQ differences has shown that it is mainly environmental, not genetic factors that are responsible for this

IQ tests contain questions that reflect the values of white, middle-class western society

As a result, minority groups are automatically disadvantaged when taking these tests