PIP: The rapid rise in world population for the 4 periods 1950-1955, 1955 -1960, 1960-1965, and 1965-1970 is mainly due to a decline in the crude death rate from 24/1000 in 1950-1955 to 16.1/1000 in 1965-1970. 1950 was a turning-point in mortality rates because for the first time public health measures became widely available in less developed regions. These less developed regions contained 63.4% of the world population in 1930, 65.5% in 1950, and 70.0% in 1970. World population increased by 22% in 1960-1970, compared to 20% in 1950-1960, which was twice as much as the 20% registered for the 20 years 1930-1950. Developed regions contributed a 14% increase between 1950-1960 and 12% between 1960-1970; in less developed regions the increases were 23% and 27% respectively. Demographic conferences have begun to neglect mortality, but this is still a vital part of total population growth. Evidence is that the mortality decline in less developed countries is beginning to level off so that previous population projections may not be reached. What decline has been seen in crude birth rates in less developed countries is largely attributable to declines in East Asia, notably in the People's Republic of China, Republic of Korea, and other Chinese or Chinese culture-related populations, as well as some of the smaller Latin American countries and some small islands off Africa. Such demographic giants as India, Indonesia, Pakistan, and sub-Saharan Africa have shown little change. In areas with high fertility there are more mothers under age 20 and more births to women over age 35 while in low-fertility areas births are concentrated in the 20-35 year groups. An interesting example is Japan which has 50% of its births to mothers 25-29 years of age. Less developed countries have a larger proportion o f the population under age 14 while developed countries which have had lower fertility for a number of years have larger numbers in the older age groups. In less developed areas the greatest burdens are associated with child-rearing while welfare for the aged is the great concern in the more developed areas of the world. The great trend toward urbanization in all parts of the world means that the population problems commanding greatest attention are those associated with large and fast-growing cities.