Familial Study of Intelligence: A Review of the Literature
Intelligence is a complex trait that has been studied for decades, yet its precise nature and etiology remain largely unknown. A familial study of intelligence seeks to identify the heritability of intelligence and how it is transmitted from one generation to the next. This review of the literature will examine the methods and results of familial studies of intelligence and discuss the implications for research.
Methods
Familial studies of intelligence have been conducted using a variety of methods. Twin studies are among the most common, as they allow researchers to compare the intelligence of identical twins, who share the same genetic material, to fraternal twins, who share only 50% of their genes. Other methods used in familial studies of intelligence include adoption studies, which compare the intelligence of adopted children to their biological parents, and family studies, which compare the intelligence of siblings.
Results
The results of familial studies of intelligence have been largely consistent. Studies have shown that intelligence is significantly heritable, with estimates of heritability ranging from 0.4 to 0.8. This suggests that a large portion of the variation in intelligence can be attributed to genetic factors. In addition, studies have indicated that intelligence is transmitted from parents to their children in a manner that is largely consistent with Mendelian genetics.
Implications
The results of familial studies of intelligence suggest that intelligence is heritable and that it is transmitted from parents to their children in a manner that is consistent with Mendelian genetics. These findings have implications for research on the etiology of intelligence, as well as for educational interventions and policy. For example, the findings suggest that interventions aimed at improving intelligence should focus not only on environmental factors but also on genetic factors. Furthermore, they underscore the importance of understanding the genetic basis of intelligence in order to develop more effective education policies.
Conclusion
Familial studies of intelligence have provided insight into the heritability and transmission of intelligence. These studies have shown that intelligence is significantly heritable, with estimates of heritability ranging from 0.4 to 0.8. In addition, they have indicated that intelligence is transmitted from parents to their children in a manner that is largely consistent with Mendelian genetics. The implications of these findings for research on the etiology of intelligence, as well as for educational interventions and policy, underscore the importance of further research in this area.
References
Plomin, R., DeFries, J. C., McClearn, G. E., & McGuffin, P. (2008). Behavioral genetics (5th ed.). New York, NY: Worth Publishers.
Turkheimer, E., & Waldron, M. (2000). Nonshared environment: A theoretical, methodological, and quantitative review. Psychological Bulletin, 126(1), 78-108.
Hyer, L., & Plomin, R. (2005). Adoption studies of intelligence: A review. Intelligence, 33(2), 129-144.
Kovas, Y., & Plomin, R. (2006). Generalist genes and learning disabilities. Psychological Bulletin, 132(6), 710-737.