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If you look in the second column of Table 11.6 "Data From Twin and Adoption Studies on the
Heritability of Various Characteristics", you will see the observed correlations for the traits
between identical twins who have been raised together in the same house by the same parents.
This column represents the pure effects of genetics, in the sense that environmental differences
have been controlled to be a small as possible. You can see that these correlations are higher for
some traits than for others. Fingerprint patterns are very highly determined by our genetics (r =
.96), whereas the Big Five trait dimensions have a heritability of 40–50%.
You can also see from the table that, overall, there is more influence of nature than of parents.
Identical twins, even when they are raised in separate households by different parents (column
4), turn out to be quite similar in personality, and are more similar than fraternal twins who are
raised in separate households (column 5). These results show that genetics has a strong influence
on personality, and helps explain why Elyse and Paula were so similar when they finally met.
Despite the overall role of genetics, you can see in Table 11.6 "Data From Twin and Adoption
Studies on the Heritability of Various Characteristics" that the correlations between identical
twins (column 2) and heritability estimates for most traits (column 6) are substantially less than
1.00, showing that the environment also plays an important role in personality (Turkheimer &
Waldron, 2000). [4] For instance, for sexual orientation the estimates of heritability vary from
18% to 39% of the total across studies, suggesting that 61% to 82% of the total influence is due
to environment.
You might at first think that parents would have a strong influence on the personalities of their
children, but this would be incorrect. As you can see by looking in column 7 of Table 11.6 "Data
From Twin and Adoption Studies on the Heritability of Various Characteristics", research finds
that the influence of shared environment (i.e., the effects of parents or other caretakers) plays
little or no role in adult personality (Harris, 2006). [5] Shared environment does influence the
personality and behavior of young children, but this influence decreases rapidly as the child
grows older. By the time we reach adulthood, the impact of shared environment on our
personalities is weak at best (Roberts & DelVecchio, 2000). [6] What this means is that, although
parents must provide a nourishing and stimulating environment for children, no matter how hard