Nature and Nurture Basis of Intelligence of Twins from 3-6 Years: An Intervention Study

Intelligence is considered as most valuable phenotypic psychological and behavioral construct having both genetic and environmental substrates. The classical twin study provided robust information regarding the contribution of nature and nurture propensities on variations of intelligence of twins. The twin investigation has been planned with the objective to assess the influence of nature and nurture on the intelligence of twins. A twin study was conducted in two districts, namely, Bhiwani and Hisar of Haryana state. A sample of 150 pairs of twins in the age groups of 3-6 years was attained from 55 villages of Bhiwani district and Hisar district. The intelligence of twins was assessed with the help of the Stanford Binet Intelligence Scale [1], whereas the home environment of twins was measured by using the Home Observation for Measurement of the Environment (HOME) [2] and the preschool environment of twin’s measure with the help of Early Childhood Environment Rating Scale [3]. The findings of heritability estimates revealed that the heritability estimates for intelligence ranging from 55-74% from 3-6 years in the Bhiwani district, whereas in the Hisar district, the heritability estimates for intelligence were 52-68 percent during 3-6 years. Analysis of variance results revealed that a significant difference in mean values was observed at ages 3-4 years among the gender of twins but no significant difference on ages 4-5 years and 5-6 years. The conclusion of heritability estimates showed that the influence of nature (genetic) on the intelligence level of twins was more than that of nurture (environment). The contribution of nature on the intelligence level of twins increases with the increase in the age of twins and the influence of nurture decreases with the increase in the age of twins. The preschool environment of twins was also significantly associated with the intellectual of twins in both the Bhiwani and Hisar districts. The intervention programme also enhanced the intelligence of twins in the age group 3-6 years in both the Bhiwani and Hisar districts.