(i) Whether intelligence is evolved or it is developed due to the environment, is a question of debate.

(ii) Lot of studies have been done to determine the role of nature and nurture.

(iii) Here we will discuss the controversy with the help of various twin studies, adoption studies and environmental studies.

On the basis of twin studies co-relation results are as follows:

(i) Identical twins reared together correlate 0.90

(ii) Identical twins reported early in childhood and reared in different environments correlate 0.72

(iii) Fraternal twins reared together correlate 0.60

(iv) Siblings reared together correlate 0.50

(v) Siblings reared apart correlate 0.25

• Adoption Studies before the Age of 6-7 Years

These studies of adopted children show that children's intelligence is more similar to their biological parents.

These studies provide evidence that intelligence is determined because of nature.

• Adoption Studies after the Age of 6-7 Years

According to these studies as children grew older tends to more closer to that of their adoptive parents.

Environmental Studies

Evidence for the influence of environment (Nurture) on the basis of Twin studies.

(i) The intelligence score of twins reared apart as they grew older, tends to more closer to that of their adoptive parents.

(ii) On the basis of differences in environment, children from disadvantaged homes adopted into families with higher, socio-economic status exhibit an increase in their intelligence scores.

(iii) Environmental deprivation lowers intelligence. Factors such as nutrition, good family background and quality schooling increase growth rate of intelligence.

(iv) There is general consensus among psychologists that intelligence is a product of complex interaction of heredity (Nature) and environment (Nurture).

(v) Heredity provides the potentials and sets a range of growth whereas environment facilitates the development of intelligence.