Nature-nurture and intelligence

Article Abstract:

Both genetic and environmental influences play a role in the development of intelligence. A study of adopted children in France shows the role of these two influences. By studying adopted children, genetic and environmental influences can be separated. Four issues are discussed: environmental influences, genetic influences, the interaction of genetics and the environment, and changes in developmental course. Adopted children, regardless of their biological backgrounds, showed intelligence quotient (IQ) levels that were approximately 12 points higher when raised by parents with high socioeconomic status than by parents with low socioeconomic status. Whether they were raised by parents of high or low socioeconomic status, adopted children of biological parents who had a high socioeconomic status had IQ levels approximately 15 points higher than adopted children of biologic parents of low socioeconomic status. These findings show the importance of environmental and genetic factors on intelligence, but neither the mechanisms for these influences nor their interaction is discussed. Research studies in mice and humans show a genetic effect on the development of the structures and systems of the brain. This may have an effect on the ability of an individual to process information. Individuals with high IQs can process information more quickly than individuals with low IQs, allowing the individuals with high IQs to use higher levels of thinking. However, IQ levels are known to change during development. The genetic and environmental influences on IQ have an effect at least until late adolescence. It is the hope of future studies that the mechanisms of these influences can be understood in order to provide children with the best circumstances for development of their IQ.

Nature and nurture, Behavior genetics, Behavioral genetics

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Assessment of effects of socio-economic status on IQ in a full cross- fostering study

Article Abstract:

Both genes and the environment play a role in the development of intelligence. A study in France involving adopted children shows that the intelligence quotient (IQ) of children is influenced by both genetic background and environmental circumstances. The study was carefully controlled, using children in the same approximate age group and sharing the same approximate age of adoption. Studying adopted children allowed separation of genetic and environmental influences. Adopted children who were raised by parents with a high socioeconomic status had IQ levels approximately 12 points higher than children raised by parents of low socioeconomic status, regardless of the children's genetic or biological backgrounds. The occupations of the two groups of parents were as extreme in socioeconomic status as possible. This shows the environmental effect in the development of intelligence. Adopted children born to parents of high socioeconomic status had IQ levels that were approximately 15 points higher than children born to parents of low socioeconomic backgrounds, regardless of the socioeconomic status of the adoptive parents. This shows the genetic effect on intelligence, but can not preclude prenatal effects, influences on the children before they were born. No interaction was seen between the environmental and genetic effects. Changes in IQ from environmental influences or genetic influences occur independently from each other, yet both affect IQ levels.

Environmental aspects, Genetic aspects, Intellect

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The democracy of the genes

Article Abstract:

The issue of the extent to which IQ is inherited has been the subject of considerable debate for many generations. Recent research indicates that genetic influences on IQ may not be as great as had been believed in the past. Indeed, significant environmental influences on IQ may take place early in life. If this is the case, then there is a strong argument in favour of public health policies which seek to reduce prenatal exposure to toxins and to boost maternal nutrition. It seems that there is a strong biological basis for human intelligence, but that this can also be subject to other influences.

Heredity

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