The theory of demographic transition is based on the historical experience of the demographic evolution of the countries in the western sphere of civilization. A number of writers have inferred that populations historically pass through different stages. Developed as an attempt to formulate a generalized expectation of the process of mortality and fertility decline in these countries, the transition theory was elaborated and received a much broader interpretation in more recent decades, when it was thought that it could also be applicable to the less developed countries still in the early stages of demographic change. In fact, transition theory has come to be increasingly considered as a theory which might anticipate the future demographic trends in countries presently in the early phases of transition. These are characterized by high population growth as a result of rapidly decreasing levels of mortality and high but more or less stable fertility levels (United Nations, 1973:58).
The demographic transition theory concerning the transition from high mortality and high fertility levels to low mortality and low fertility levels was based
on European experience, where fertility decline in most cases was accompanied by or preceded by decline in mortality. The mainstream arguments of the theory are that fertility is high in poor, traditional societies because of high mortality, the lack of opportunities for individual advancement, and the economic value of children. All these things change with modernization and urbanization. In this situation individuals can make use of the new opportunities if their viewpoints become reoriented to the changes that have taken place (Caldwell, 1976:324).
According to Notestein et al. (1944), a continued decline in fertility and the emergence of the small family pattem in Europe is in major part due to the voluntary control of fertility, principally through contraception. The driving force stimulating such control lies in socio-economic incentives. Modem urban society places a high value on the individual as opposed to the family or other groups, sets great store by the advancement of individual health, education, social and economic status, and makes childbearing an expensive undertaking. There are strong inducements to parents to have only a few children to whom they can give 'every advantage'. These inducements have been strong enough to bring fertility to very low levels (Notestein et al., 1944:30).
Thus Notestein (1952:13-31) maintains that changes in fertility and mortality took place in conjunction with economic development in the west. The important factors that are believed to have caused the reduction in fertility were: the growing importance of the individual rather than the family, and particularly the decline of extended family group; the development of a rational and secular point of view; the growing awareness of the world and modem techniques through population education; improved health; and the appearance of alternatives to early marriage and childbearing as a means of fulfilment and prestige for women. Notestein particularly emphasized the role of popular education which might stimulate an innovative and rational view of life, enhance the importance of the individual as opposed to the extended family group, improve the status of women, and substitute the ideal of a healthy, prosperous family for that of a large family.
Notestein (1952) argued that the study of the beginnings of economic development and demographic transition in certain non-European countries suggested that the principles drawn from the European demographic transition would be widely applicable in the world. While the idea of a demographic transition has been widely adopted and is frequently used as a generalized description of the evolutionary process, a number of writers have emphasized its limitations as a theory. It has been argued that since the transition is limited to the experience of western countries, whose historical demographic trends were by themselves far from uniform, it is unlikely that it provides more than vague suggestions about factors which may determine population growth in other countries (United Nations, 1973:59).
Since the idea of the demographic transition was fully formulated there has been an unprecedented flood of demographic research and profound changes in birth and death rates in most populations of the world (Coale, 1975:347). The weakness of the demographic transition concept became apparent when the process of demographic change in European countries was examined in greater detail using historical demographic records. The concept fails to define the specific levels of a set of variables that are required for fertility decline. To Coale (1975:352), the weakness of the concept is associated with the difficulty of defining a precise threshold (a check-list of essential characteristics or a combined score on some socio-economic scale) of modernization that will reliably identify a population in which fertility is ready to fall. He attempted to modify the concept of threshold to allow for cultural differences in different parts of the world. Since there was a wide diversity of circumstances in which marital fertility declined, and the consequent difficulties of formulating a well-defined threshold, Coale (1975:352-353) indicated the following three general prerequisites of a major fall in marital fertility:
(1) Fertility must be within the calculus of conscious choice. Potential parents must consider it an acceptable mode of thought and form of behaviour to balance advantages and disadvantages before deciding to have another child;
(2) Reduced fertility must be advantageous. Perceived social and economic circumstances must make reduced fertility seem an advantage to individual couples;
(3) Effective techniques of fertility reduction must be available. Procedures that will prevent births must be known, and there must be sufficient communication between spouses and sufficient sustained will, in both, to employ them successfully.
Kirk (1969:93) held the view that cultural barriers and lagging socio-economic development have blocked the spread of fertility reduction into the developing regions. He argued that attempts to establish fertility decline thresholds should concentrate on cultural factors or cultural regions, such as Latin America, East and Southeast Asia, Muslim countries, African countries and so on to define more homogeneous regions where there might be a better chance of identifying the levels of development required before fertility decline can occur. He saw the great importance of culture in influencing fertility declines and that socio-economic factors act within given cultural settings which themselves have a strong influence (Kirk, 1967:72-86; 1971:125).
Many less developed countries have high fertility but have witnessed a sharp decline in mortality. The factors that kept the fertility levels in these countries high were explored by Davis (1957:88-95). According to Davis, the rise of industrial nations has had an impact on the less advanced areas and has brought commerce and political change and a marked decline in mortality. But it has not fundamentally altered the agrarian character of the society and to this extent has not forced a change in the institutional structure. He argued that institutional factors were responsible for high fertility in developing world. He elaborated that the family is the key in analyzing the institutional factors responsible for fertility, because human society accomplishes the function of bearing, nourishing, and socializing children primarily through the universal instrumentality of the nuclear family. Therefore, it is through the relations of the nuclear family to the rest of the society that the social factors controlling the level of fertility can be observed (Davis, 1957:89).
Davis (1957:90-92) argues that the subordination and incorporation of the nuclear family by wider kinship groups in developing countries are conducive to abundant reproduction in many ways. First, the economic cost of rearing children does
not impinge directly on the parents to the same extent that it does where the nuclear family is a more independent unit. Second, the inconvenience and effort of child care do not fall so heavily on the parents alone. Third, the age at marriage can be quite young, because under joint household conditions, there is no necessary implication that the husband must be 'able to support a wife and family' before he gets married. Fourth, with an emphasis on kin solidarity the compulsion to marry is often quite strong. Fifth, the young wife is encouraged to have offspring as early as possible and in considerable number. Given the joint family and the prevailing rule of patrilocal residence, the bride is a stranger among her husband's relatives. She is often assigned a low position in the restricted hierarchy of women. She has little she can call her own until a child is born. The birth of a son proves her contribution to her husband's line and thus begins her rise to a higher position within the domestic circle. Sixth, the man is strongly motivated to demand offspring. Often the children are viewed as belonging to him and can provide security for in old age even when few other means are available.
Davis (1957:92-93) further points out that an additional influence on fertility is the tendency of stable agrarian societies to segregate sharply the role of men and women. The effect of such a limitation is to confine women largely to the household and to identify them with reproduction, so that their lives revolve around home and children. Education of women and girls is regarded as unnecessary, if not immoral. Women, therefore, have little knowledge, sophistication, or independence. They cannot conceive of a role, such as a career role which would compete with the childbearing role. With the segregation of roles, the gulf between the man's and woman’s world becomes so wide that communication between husband and wife is reduced to a minimum, particularly with reference to sexual topics, because the woman is supposed to have no knowledge or initiative in such matters. The husband views reproduction as his prerogative, something taken for granted and involving simple compliance on the wife's part.