Prostitution is closely related to urban life and mobile populations. In primitive tribes it is virtually unknown, although promiscuity before marriage, and polygamy or polyandry, may be accepted. Economic factors are important reasons for going into prostitution, which is often very marked in poverty stricken areas where there is little employment for either men or women, or among indigenous tribes which have suffered cultural invasion and have not been able to adapt economically to a new way of life. Frequently there are social reasons also; broken families, disgrace that comes with abandonment by a boy friend, pregnancy and single parenthood, encouragement or outright sale by parents and violence in the family. Prostitutes may be very young and coerced into prostitution. Children who are gaoled for vagrancy are bailed out by recruiters of prostitutes and forced into the trade. So-called employment agencies recruit women from poor areas, promising jobs, paying their parents in advance and then forcing them into prostitution.