This paper summarizes research on the effect of population growth on e
nvironmental quality. Land transformations induced by the spatial expa
nsion of agriculture are probably the major route by which population
growth has affected features of the natural environment. These transfo
rmations are not automatic and their extent is influenced by social in
stitutions. Intensification of agricultural land use is an alternative
response with its own set of environmental implications. These are es
pecially salient in the case of expanded irrigation. In contrast to re
lations in the agricultural sector, a new version of the conventional
I = PAT equation is introduced to suggest that population growth is a
minor influence on the extent of industrial pollution. Nevertheless, p
opulation policy may play a useful role in strategies to reduce indust
rial pollution.