FIGURE 7.8 Genetics, Environment, and IQ Scores This graph shows the average correlations of IQ scores for individuals who are genetically related to different degrees. The graph is based on research by psychologists Thomas Bouchard and Matt McGue, who summarized the results from more than 100 separate studies on over 100,000 pairs of relatives (McGue & others, 1993). The data show that both genetics and environment have an effect on IQ scores. The more closely two individuals are related genetically, the more similar their IQ scores: Identical twins reared together are more alike than are fraternal twins reared together. However, the same data also show the importance of environmental influences: Identical twins reared together are more alike than are identical twins reared apart, and siblings who are reared together are more alike than are siblings reared in different homes.
Source: Research from McGue & others (1993).