Chapter 4 deals with nature versus nurture. Researchers can tell at ages as young as 4 months which children will be highly reactive and which less reactive. Highly reactive babies respond with stress to new situations. Highly reactive children are more likely to be introverted. It may be that introversion just indicates more sensitivity to environment. Up to 50% of introversion may be based on hereditary factors.
Cain tells of Dobbs’s Orchid hypothesis. Many children are like dandelions and will do well anywhere. Others, including highly reactive children wilt easily, but under the right conditions grow strong and magnificent. This seemed a weak metaphor to me since that kind of variability could apply to any population. Cain backed it up by citing some research and by noting that 1/4 of the highly reactive children suffer from social anxiety disorder. In summary children who are highly reactive do better than average socially in a nurturing environment and worse than average in a stressful environment. This may be related to the length of an allele that helps produce serotonin.