1148 PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28

stages. Two factors that affect the demand for agricultural
products are responsible for this — population growth and the
income elasticity of demand. One of the well known effects
of the early stage of economic growth is a decline in mortality.
 The improvement of sanitation, the availability of medicines
 and medical facilities, the improvement of the quantity
and quality of the food supply, the reduction in famines due
to improved transportation, and the control of certain endemic
diseases have a significant and short run effect upon death rates,
especially of infants and children. There is almost nothing that
occurs during the early stages of economic development that
has an effect on fertility. Thus there is a very strong probability
 that the rate of population growth will be higher during
the early stages than in the later stages of economic development
 and that at a given time higher for low income countries
than for high income countries (1).
It has been noted above that the income elasticity of demand
 for food is higher at low than at high income levels. Thus
if a high and low income country have the same growth rate
of per capita income, the income effect on demand will be substantially
 greater for the latter than for the former. The two
effects are illustrated by Table 1, which presents certain projec-‘ions
 made by FAO for a period of roughly a decade.
The estimates of population increase are relevant to the
comments made above. The three low income areas have

(!) This statement is based on the assumption that the growth in food
output is enough to sustain the growth in population. If the conditions
implied by a Malthusian model of economic growth apply, the growth of
population will depend upon the growth of food output.
The statements in the text about the relationship between population
growth and income levels are admittedly very crude and approximate generalizations.
 Obviously there are many factors that influence population
growth. The difference in population growth rates in Western Europe
and the United States can not be explained by the difference in the level
of per capita income. An interesting article by IRMA ADELMAN (An Econometric
 Analysis of Population Growth, « American Economic Review »,
vol. LIII, No. 3, June 1063, 314-30) provides some support for the view
expressed in the text

16] Johnson - pag. 8