quiet-the-power-of-introverts-in-a-world-that-cant-stop-talking-susan-cain

from twin studies show that
introversion-extroversion is only 40 to
50 percent heritable. This means that,
in a group of people, on average half of
the variability in introversion-extroversion
is caused by genetic factors. To
make things even more complex, there
are probably many genes at work, and
Kagan’s framework of high reactivity is
likely one of many physiological routes
to introversion. Also, averages are
tricky. A heritability rate of 50 percent
doesn’t necessarily mean that my introversion
is 50 percent inherited from my
parents, or that half of the difference in
extroversion between my best friend
and me is genetic. One hundred percent
of my introversion might come from
genes, or none at all—or more likely
some unfathomable combination of
genes and experience. To ask whether
it’s nature or nurture, says Kagan, is
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