Owing to the combination of a number of unprecedentedly powerful factors (heavy density of settlement in agricultural areas, wide and probable growing difference between rural and urban levels of income, very rapid growth in the number and proportion of young people who have been to school), the rural-urban drift has proceeded in most countries at a very fast pace. This movement has resulted in a very serious disequilibrium in the job supply/demand situation in the urban areas, an imbalance which is reflected in a swelling of the tertiary sector, considerable underemployment in a number of sectors and, in particular, urban unemployment which has reached extremely high rates in a large number of developing countries.
The rapid growth of the urban population in developing countries is largely due to rural migrations which, given their social and economic origin, are less predictable than are the other two growth factors, fertility and mortality rates. Some migratory movements are encouraged by the reality of growing urban industries, but it is mainly the erratic migrations from destitute rural areas, motivated by despair rather than by definite objectives, which furnish the greater part of the displaced peasants flooding the urban labour market in the cities of Asia and Latin America. Long years of unemployment gradually undermine their moral and physical strength and further reduce their chance for future economic and social advancement.
Gradually, as a result of a reduction in the daily number of hours of work and an extension of the holiday periods which replace the numerous feastdays of traditional societies, there has been a return in the economies of the developed countries to an annual number of working days similar to, or even lower than, the number that had been customary prior to the Industrial Revolution. Yet, in assessments of the level of underemployment in developing societies, there is a tendency to regard the reduced number of hours of work in the developed countries as an unprecedented situation due to the high levels of productivity which modern technology has made feasible. In the South, another factor, which is generally overlooked, consists in the coercive influence of climate. Without taking any narrowly deterministic view of geography, there can be no doubt that the tropical, or semi-tropical, climate which reigns in the greater part of the Third World is less well suited, especially in certain seasons, to long hours of work than is the climate of the temperate regions in which the majority of developed countries are situated.
Since World War II there has been a net emigration of over 150 million persons to urban areas. The scale of this movement, to which is added a considerable natural increase in the population of towns (due to a high birth rate and a reduced death rate resulting from the age composition of the population), has led to an extremely rapid growth of the urban population during this period, which increased at an average rate of over 4.5% a year. The 750 million jobless in the Third World in 1975 is expected to increase to 1,320 million by the year 2000. Meanwhile, the number of new jobs needed is expected to be 630 million in Asia, 250 million in black Africa, 190 million in Latin America (as compared with 360 million jobs needed in Western countries). Figures for 1975 show that whereas unemployment as a whole in the developing countries was 5% of the total labour force, rural unemployment was 3.6% and in the towns 8% of the potential workforce was jobless.
Although incomplete, the available estimates for Latin America reveal very high rates of urban underemployment, ranging from 20% and upwards in most countries. Estimates of urban underemployment in other regions are even scantier, although it is clear that urban underemployment exists everywhere. A broader but perhaps more significant indicator of the extent of urban underemployment than such non-comparable statistics is to be seen in the swelling of tertiary employment activities that characterize the great majority of developing countries.