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Influence of Heredity & Environment on intelligence


Today researchers agree that heredity and environment have an interactive influence on intelligence. Heredity places an upper and lower limit on the IQ that can be attained by a given person.

Influence of Heredity and Environment on intelligence

Today researchers agree that heredity and environment have an interactive influence on intelligence. Heredity places an upper and lower limit on the IQ that can be attained by a given person. The environment determines where within these limits the person’s IQ will lie. Studies on identical twins with respect to intelligence showed that the average correlation in identical twins was and investigations of fraternal twins produced an average correlation of 0.67.

When reared together identical twins had intelligence correlation upto 0.89 with those twins reared separately and fraternal twins reared together and separately the average correlation was 0.78 a mere 0.11 difference. If the environmental factors were more important than the genetic factors the defense would have been very high. Adoption studies also show that adopted children somewhat resemble their biological parents in intelligence researchers have found that IQ scores of adopted children more highly correlation with that of their biological parents than that of their adaptive parent’s IQ.

Because of strong genetic link between the adopted children and there biological parents it can be concluded that heredity is more important than environment. Researchers have also found that heritability of intelligence increases from as low as 0.45, in infancy to as high as 0.80 in late adulthood. This is because as we grow older, the effect of environment reduces upon us and we interact more with the environment as we like not under our parent’s pressure or the of society.

Example: Sometimes parents push children to become engineers / doctors, incompatible environments, but as adults these individuals may select their own career environments.

The heritability index has several flaws as it greatly depends on the data fed into its calculation. The data is collected from traditional IQ tests which is deemed by some experts as not the best indicator of intelligence. Also heritability assumes that both environment and heredity are separate factors and each excerpts a distinct amount of influence but genes and environment works together, with the environment shaping the genetic activity. Children are not predestined to have an intelligence level similar to their biological parents.

Example: Most children of extra ordinary intelligence were born to average intelligence parents. Genetic ancestry of a child is not a 100 % or surefire predictor of his / her intelligence environment also makes an appreciable difference as we shall now see.

Today most researchers agree that modifications in environment can change the IQ scores of individuals considerably. Biological unrelated children raised together in the same home have some similarity in IQ. A correlation of 0.25 exists for unrelated children reared together in the same environment moreover, blacks who are raised in economically enriched environments have IQ score similar to whites in comparable environments.

Example: in a study of black children adopted by middle class while families at an early, the IQ of the adopted children average 15 point above the IQ scores of unadopted black children the racial gap in IQ narrows considerably after college education.

Example: in a study of Indian children in south Africa whose schilling was delayed for 4 years due to the non-availability of teachers, it was found that they lacked 20 points on IQ tests as compared to children who had access to education.

Another possible effect of education can be seen in rapidly increasing IQ scores around the world. This can also be termed as “ Flynn Effect” the average person today has IQ score more than the average person a 50 years ago.

If a representative example of people took 1932 Stanford Binet test today about 25% will be defined as having very superior intelligence. Usually only 3% of the population can be accorded “superior intelligence” the increase in intelligence as shown by Flynn effect is not due to heredity as it has taken place in a very short span and thus environment is the main factor, such as the enormous amount of information, devices, technology and people that we are exposed to daily through tv radio, internet, socializing etc.

Severe malnutrition before as well as after the birth can limit neurological development having a long term effect on cognitive abilities as well as intelligence. Attention, memory abstract reasoning and general school achievement are likely to suffer when the child is facing malnutrition all these contribute towards intelligence.

Correlation studies indicate that stimulating home environment such as parents interaction more frequently with their children, making learning and reading materials available, use of complex structures in sentences encouraging development of new skills and so on are associated with high IQ scores in children.

In a study in Romania, orphans were placed in large institutions to be raised for some children foster parents were found and the children were raised by foster parents dramatic differences between the two groups were found despite adequate nutrition, average IQ was found to be 64 mentally retarded, where as foster children had IQs in the normal range, the foster children also exhibited more brain activity.

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