In spite of greater information on sexual matters and greater availability of contraceptives, and the relaxation of norms on sexuality and marriage in many societies, this is, in the same societies, paralleled by a growing incidence of illegitimate births. Also, children born out of wedlock are less frequently than previously abandoned to charitable or public institutions for adoption by foster parents. Single women and unmarried couples belonging to the middle classes of affluent societies, are increasingly content to have children, but unwanted 'illegitimate' births are still mainly found among the poorer social groups.
Illegitimate children are children born out of wedlock in infringement of a society's regulations of procreation. They may be the result of poverty, inadequate education, family breakdown, cohabitation, the non-validity of divorce, inadequate contraception, prostitution, promiscuity, slavery or war. Definition of illegitimacy depends on the law. For example, children of a polygamous marriage will be legitimate in a society where polygamy is legal; but they will be illegitimate if monogamy is the law.
Illegitimate children represent between 10 and 17% of total annual births in the developed countries. In some of these countries, this proportion of illegitimate births doubled during the 1960s and 1970s. In all of them, the trend is on a steady increase since the beginning of this century. At present, the bulk of this increase is among young women in the 15-20 age group. Such births occur more often in poorer social groups. In the USA in 1979, 55% of all black children were born out of wedlock, as compared with less than 10% of all white children; in 1988, two out of three birth were to single mothers. In the USA in 1988, 25% of birth were to an unmarried mother, namely about 1 million births. This represented an 8% increase on the previous year and a 51% increase on 1980. In other less economically developed societies, illegitimacy rates are also very high. In some Latin American countries, they reach 50 to 60% of all births, because consensual unions are so frequent that the frontiers between such unions and legal marriages are blurred.
In Sweden 46% of children were born out of wedlock in 1987. In Denmark and Iceland nearly one half of newborns are non-marital. In Norway, Austria, France and the UK it is one in four or one in five.
In the UK the number of birth outside marriage rose from 54,000 in 1961 to 236,000 in 1991, whilst births inside marriage fell from 890,000 to 556,000.