The study of the heritability of IQ investigates the relative importance of genetics and environment for phenotypic variation in intelligence quotient (IQ) in a population. "Heritability", in this sense, "refers to the genetic contribution to variance within a population and in a specific environment". There has been significant controversy in the academic community about the heritability of IQ ever since research began in the 19th century.
IQ is a polygenic trait under normal circumstances according to recent research. However, certain single gene genetic disorders can severely affect intelligence, with phenylketonuria as an example.
Estimates in the academic research of the heritability of IQ have varied from below 0.5 to a high of 0.9 (of a maximum of 1.0). IQ heritability increases during early childhood, but it is unclear whether it stabilizes thereafter. A 1996 statement by the American Psychological Association gave about .45 for children and about .75 during and after adolescence. A 2004 meta-analysis of reports in Current Directions in Psychological Science gave an overall estimate of around .85 for 18-year-olds and older. The New York Times Magazine has listed about three quarters as a figure held by the majority of studies.
Read more about Heritability Of IQ: Heritability and Caveats, Estimates of The Heritability of IQ, Heritability of Giftedness, Molecular Genetic Investigations, Correlations Between IQ and Degree of Genetic Relatedness, Between-group Heritability