An Intervention Study: Genetic and Environmental Interplay for Fluid Intelligence of Twins during Early Childhood

Abstract

Twin studies are a key method in quantitative genetics, estimating genetic and environmental influences on individual differences in traits like intelligence. Fluid intelligence, a core component of general intelligence, is influenced by both genetic and environmental factors, with heritability increasing with age. The present twin study aimed to examine the relative contributions of genetic and environmental factors to fluid intelligence in early childhood and evaluate the impact of a structured home-based intervention. Snowball sampling was used to collect 150 twins included both monozygotic and dizygotic pairs, aged 3–6 years, from Bhiwani and Hisar districts, Haryana, India. The intervention package was administered to the experimental group of twins for a period of eleven weeks in the home settings of twins, and the activities were conducted with twins for approximately 60 minutes weekly sessions, in order to ensure that activities were exchanged between participants, and maximum possibilities for exercise. Fluid intelligence was assessed using the Stanford-Binet Intelligence Scale before and after the intervention. Results showed significant differences in fluid intelligence across age groups. Post-intervention assessments revealed notable improvements, indicating the effectiveness of environmental stimulation. Heritability estimates suggested that genetic variation accounted for 40–70% of the variance, with monozygotic twins exhibiting higher intra-pair correlations than dizygotic twins. The study concluded that while genetics plays a substantial role in fluid intelligence, environmental enrichment can significantly enhance fluid intelligence. Moreover, the influence of genetic factors appeared to increase with age within the early childhood period.