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Joseph M. Horn is an American psychology professor known for his work on adoption studies.

Horn received his Ph.D. from the University of Minnesota and currently teaches at the University of Texas at Austin. Research interests include intellectual and personality development, behavior genetics, personality, individual differences, and vocational behavior.

Horn is a Pioneer Fund grantee. Of interest to the Pioneer Fund is Horn's Texas Adoption Project started in 1972, a longitudinal study of over 500 adopted children, their biological mothers, and adoptive parents and siblings. According to the Pioneer Fund website, Horn's work is evidence of a hereditarian influence:

The first phase of the study tested the personality and intelligence of adopted children between three and fourteen years-old; then the study re-tested them again as adolescents and young adults ten years later. Not only were the adoptees much more like their biological mothers than their adoptive mothers, but as they grew older, they became increasingly more similar to the biological parents they had not seen since shortly after their birth, and the less like the adopting parents who had raised them. By adolescence, the adoptees showed virtually no similarity to their adopting parents or the adoptive siblings with whom they had been raised. The study concluded that about fifty percent of the individual differences in IQ and personality were due to heredity and the remainder to environmental influences.

In 1994 he was one of 52 signatories on "Mainstream Science on Intelligence," an editorial written by Linda Gottfredson and published in the Wall Street Journal, which defended the findings on race and intelligence in The Bell Curve. ^[1]

• Horn, J. M., Loehlin, J. C., & Willerman, L. (1979). Intellectual resemblance among adoptive and biological relatives. Behavior Genetics, 9, 177-207.
• Horn, J. M. (1983). The Texas Adoption Project: Adopted children and their intellectual resemblance to biological and adoptive parents. Child Development, 54, 268-275.
• Loehlin, J. C., Horn, J. M., & Willerman, L. (1990). Heredity, environment, and personality change: Evidence from the Texas Adoption Project. Journal of Personality, 58, 221-243.

• Joseph Horn webpage at University of Texas at Austin
• Highlights of Pioneer Fund Research and Grantees