Although puberty has a biological basis in that it is marked by sexual maturity, including the ability to either engender or bear children, childhood itself, as a prolonged and distinctive life phase is socially constructed rather than biologically determined. In very primitive societies, children start working as soon as they are physically capable of being useful rather than burdensome. Although positions of great responsibility are reserved for those with greater wisdom and experience, and certain activities reserved for those past puberty, not all societies consider childhood a period in which the individual is psychologically distinctive or treated as other than a smaller, more ignorant, but otherwise not distinctive member of the social group.