Heritability as a
Phenotype x Genotype correlation
Consider a set on educational test scores
for six children (C)
born to one set of
parents and adopted by another set. The mean score of the
birth parents (B)
(calculated as the
is 95. The
average score of the adoptive parents (A) is 115, 20 points higher
than that of the birth parents. After adoption, the
children are provided with an "enriched" educational environment. Upon
testing, they achieve the same average score (115) as their adoptive
What does this tell us about the heritability of scores?
Note that each of the children is exactly
20 points higher than the average of the birth
(and thus the heritability
between them is therefore rBxC = 1.0. The adopted
children achieve exactly the same mean score
as the adoptive parents.
However, the range of
the difference is scattered from -8 to +6 points: the
correlation between them is rCxA ~ 0. [The correlation
between birth and adoptive parents is also rBxA ~ 0,
which shows that the adoptive parents have not selected
children based on expected performance].
That is, a trait that is perfectly heritable may
be perfectly changeable
by a modification of the environment. Modified the environment increases
the trait mean, but does not improve any particular
individual in a specific way.
example after Griffiths et al. (2002); All text material ©2014
by Steven M. Carr