Traditional psychology thinks of functional families as lacking conflict. A traditional psychologist might label familial strife as dysfunctional but evolution actually predicts- if not demands- a certain level of conflict within families. Every individual in a family has her or his own reproductive interests that have to interact with the reproductive interests of everyone else. A child that helps raise a younger sibling may be passing on part of her or his genes at the expense of being able to mate and pass on the whole package.
