The effects of genetic and environmental factors on IQ
For the last 140 years, scholars have been avidly trying to identify the exact factors that influence one’s IQ. The numerous studies on the subject have led most scientists nowadays to the belief that one’s IQ is determined by a variety of both genetic and environmental factors, although there is contention about the exact weight of each.
The majority of studies on intelligence have shown that environmental factors account for about 25% of the differences in people’s IQ scores. The factors that have been of greatest interest to scholars include prenatal development, nutrition, birth order, home and family environment, and the effects of schooling.
Prenatal development
Scientists have discovered many factors during a woman’s pregnancy that could affect a child’s cognitive development. Among them are:
Nutrition
Despite researchers’ initial belief that nutrition played a significant role in a child’s cognitive development, so far, there has been no substantial evidence that differences in nutritional habits have a noticeable effect on IQ, unless a child has suffered severe and prolonged malnutrition in early childhood.
Birth order
Surprisingly, statistical data show that birth order can somewhat affect IQ:
Home and family environment
One of the factors that many people attribute an important role to in mental development and differences in IQ is home and family environment. The latter encompasses variables such as:
Schooling
In addition, scholars have also examined the effects of schooling on a child’s IQ. They have discovered that differences in school quality have no detectable influence on a child's intelligence test scores. What proves to be of greater significance is regular school attendance, especially in elementary school.
Genetic factors
Besides environmental influences, most scientists today believe that genes also play a part in determining one’s IQ. However, there is currently an intense debate whether genetic or environmental factors are the deciding influence.
To sum up, science has come a long way in understanding the different factors that shape one's intelligence. However, there are still contentious issues that need to be clarified.
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References:
Jensen, Arthur R. Straight Talk About Mental Tests. New York: The Free Press, 1981. 168-190.