shyness

Shyness may be the result of deficits in two areas of the brain. A new study found that people who identify themselves as inhibited may have deficits in the amygdala and the hippocampus regions of the brain. The researchers drew this conclusion after they used functional magnetic resonance imaging (fMRI) to examine shy adults with either an inhibited or uninhibited temperament.

And if it has to do with brain structure, then shy adults are more likely to have shy kids. This also means that there is probably a REASON for this–perhaps their shy ancestors survived because they hid when dangerous individuals were near, rather than stepping up to interact with them.
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