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 mortal- 
ity. The improvement of sanitation, the availability of medi- 
cines 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 proba- 
bility that the rate of population growth will be higher during 
the early stages than in the later stages of economic develop- 
ment 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 de- 
mand 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 sub- 
stantially 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 gene- 
ralizations. 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 Econo- 
metric 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