Intelligence What are the influences of environment and heredity on measured intelligence? Psychologists are greatly divided over whether heredity or environment has a more dominant influence on individual intelligence. Although some animal studies appear to suggest heredity have the greatest influence, a seemingly more accurate conclusion may be drawn form human studies on intelligence. In studies on the similarities between IQ of siblings reared in the same and separate environments, the IQ of fraternal twins reared together showed greater similarity than the scores of ordinary siblings. One may wonder why this is so! Parents tend to treat twins more alik