Answer to Question 1
Shared environmental influences tend to influence positive aspects of temperament like smiling, sociability, and soothability. But shared environmental influences do not seem to influence activity levels or negatively toned aspects of temperament, like irritability or fearfulness. Instead, nonshared environmental influences tend to influence those more negatively-toned aspects of temperament. As parents notice that a child does NOT like something, they tend to let them avoid that thing, increasing the aversion to that object or situation. This amplifies the tendency towards fearfulness, for example. Alternately, if one child is more irritable than a sibling, the crabby child tends to produce more negative emotions in the parents who then in turn may be more short-tempered with the crabby child. This short-temper may provoke more irritability in the child who was more irritable to start with, and produces a nonshared environmental influence between siblings that influences negative aspects of temperament.
Answer to Question 2
C
Four hypotheses on how populations might relate to one another along an environmental gradient.
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