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.
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.