Thus the combination of continued high fertility and greatly reduced mortality in the less-developed countries raises the levels of investment required while impairing the capacity of the economy to achieve high levels of investment. Economists have estimated that a gradual reduction in the rate of childbearing, totaling 50 per cent in 30 years, would add about 40 per cent to the income per consumer that could be achieved by the end of that time.
To recapitulate, a short-term increase in per capita income may be possible in most less-developed areas, even if the fertility rate is not reduced. Nevertheless, even in the short run, progress will be much faster and more certain if the birth rate falls. In the longer run, economic progress will eventually be stopped and reversed unless the birth rate declines or the death rate increases. Economic progress will be slower and more doubtful if less-developed areas wait for the supposedly inevitable impact of modernization on the birth rate. They run the risk that rapid population growth and adverse age distribution would themselves prevent the achievement of the very modernization they count on to bring the birth rate down.