1Cademy - IQ Correlation and Genetic Relatedness

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IQ Correlation and Genetic Relatedness

Research indicates a positive relationship between genetic relatedness and intelligence quotient (IQ) scores, demonstrating that as individuals share a greater proportion of genes, the correlation between their IQ scores increases. For individuals who share no genes, such as adoptive parent-child pairs, adoptive siblings, or unrelated children raised together, the IQ correlation ranges from roughly 21 percent to 32 percent. This correlation rises to approximately 33 percent for half-siblings, who share 25 percent of their genes. For those sharing 50 percent of their genes, including parent-child pairs and fraternal twins raised together, the correlation increases to about 44 percent and 62 percent, respectively. The strongest relationship is observed in identical twins, who share 100 percent of their genes, exhibiting an IQ correlation of nearly 80 percent, even when raised apart.

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Updated 2026-05-02

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OpenStax Psychology (2nd ed.) Textbook

Group	IQ Score Correlation
Identical Twins (reared in separate homes)	0.76
Fraternal Twins (reared in the same home)	0.58
Adopted Siblings (reared in the same home)	0.29