Nature, nurture & the IQ

Rajendra Prasad Pangeni


Everyone wants to be more intelligent. Everyone wants to get more marks in mathematics and pass interviews easily. But intelligence cannot be developed within a few days. It is also some-thing inherited as genes that you are carrying and is governed by multiple environmental factors. In many cases, it is found that there is difference in intelligence level among members of the same family, growing in the same family environment. In other cases, family members or even twins reared apart and growing in different environments possess similar levels of intelligence. Yet from research carried out on some identical twins on the basis of IQ tests, it can be safely concluded that social and educational environmental differences may strongly affect intelligence despite genetic similarities. In some experiments conducted, a particular pair of twins who were reared apart differed by 24 IQ points; one completed college and became a schoolteacher while the other, did not finish school. But this may also have happened due to lifestyle choices.

Another pair of twins reared apart differ only by 1 IQ point although one was raised by a well-to-do physician while a truck driver raised another. This finding shows that the identical twins reared apart do not achieve the same differences in IQ scores. It also points to the possibility that the genetic similarities influencing that portion of intelligence measured in this fashion are not completely thrown off track by environmental differences. Existence of the genetic factor can also be measured in another fashion. The closer the relationship between two individuals, the more similar their IQ test scores. Thus, the IQs of children and their natural parents are more closely correlated than the IQs of children and their foster parents. At the same time, however, individuals with the same degree of relationship who were reared together show more similar IQ test scores than those reared apart. Therefore, it is found that both genetic and environmental factors play a role in intelligence.

Some factors that affect intelligence are as follows.

Size of family

A number of studies have shown that greater the number of children in a family, the lower the IQ per child. The IQ level depends to some degree on the attention given to an individual during his development and children in large families usually have less opportunity of getting adequate attention. More interestingly, the particular birth order of a child in a family is believed to be associated with intelligence. It is found that the first-born child achieves better IQ scores than his later-born siblings. The reason is still unknown and it can hardly be caused by basic genetic differences.

Cultural effects

IQ differences have been shown to exist, up to a certain extent, between regions in a country and occasionally between religious groups and races. A number of instances are known in which IQ scores have significantly increased when children were given social and educational opportunities unavailable to their parents. This is termed as cultural modifications. At the same time, institutionalised youngsters living under poor social and physical conditions often show gradual decline in IQ performance. A comparative increase of approximately 50 IQ points have been observed among orphans who were adopted or received special enrichment before the age of two.

Early environment

The development of the perceptive and problem-solving skills that are reflected in intelligence scores often depends up on stimuli and encouragement that infants and young children receive. It is known that experimental animals deprived of stimuli during early ages will show intellectual retardation. In humans, the early stimuli depend on the mother.


It is seen that protein deprived females will produce offspring with a reduced number of brain cells. This effect is also accompanied by kidney deficiencies and other severe body difficulties. Therefore, dietary deficiencies caused by social and economic factors play a role in IQ. The tests on relationships between IQ scores based on family size, birth order and social grouping were performed during 1963- 1966 on about 40,000 males in Netherlands, all 19 years of age, who were examined to determine their fitness for military duty.