390 
The wet forested lands of the hot 
belt, which are included in the culti- 
vable land of our estimate, offer the 
chief possibilities of any considerable 
extension of the cultivated land. 
Everyone who has studied the matter 
must have been impressed by the con- 
trast between the island of Java, 
which supports a population as dense 
as that of England, and the unculti- 
vated wastes of forest and savanna 
which occupy the greater part of the 
hot lands. A few other small tracts of 
these lands are relatively well culti- 
vated and populous, as in parts of the 
African Lakes region, the Benue 
Valley of Nigeria, and parts of Upper 
Guinea. In South America there 
seem to be no correspondingly popu- 
lous patches, though the vast Amazon 
lowland is a region very favorable to 
vegetable life. Here the chief obsta- 
cles to cultivation appear to be (a) the 
combination of heat and humidity, 
which forms a most enervating cli- 
mate, (b) the very marshy character 
of much of the region, which is deltaic 
in character and can only be re- 
claimed for cultivation by a great 
expenditure of labor, (c) the density 
of the jungle and the rapidity of 
plant growth, (d) the scarcity of labor, 
and (e) the lack of any immediate in- 
centive strong enough to induce any 
civilized people to attempt the task of 
colonizing in this region. 
It is significant that the chief crops 
which are now under cultivation in 
the hot lands are broadly divisible into 
two distinct categories. The one in- 
cludes the trees or shrubs of the plan- 
tations whose produce forms a money 
crop for export to the populous lands 
of the midlatitude zones, such as tea, 
coffee, rubber, bananas, oil palms. 
These are usually grown on well- 
drained slopes in the hilly areas. The 
other consists of local food plants, such 
as the rice and associated annuals of 
the wet irrigated flat lands of the deltas 
and valley bottoms of the East Indies. 
Up to the present, the efforts of 
European and North American 
planters in the hot lands have been 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1948 
directed mainly to the first group of 
products, and therefore to areas of 
considerable relief. Their plantations 
and habitations avoid the wet and 
marshy lowlands. Only incidentally, 
through the growth of a local food 
supply for their work people, have 
they developed cultivation of the 
second type, as in the rice fields of the 
Guiana coast. Yet the experience of 
the planters has sufficed to show the 
nature of many of the obstacles to be 
overcome in bringing the fertile lands 
of the hot belt under cultivation. It 
justifies the prediction that these lands 
will only be reclaimed for man under 
great economic pressure, and at the 
cost of enormous amounts of labor. 
The peoples of the temperate regions 
are not likely to migrate to the hot 
lands in any considerable numbers so 
long as they can find room in the more 
attractive lands of their own climatic 
zones. ‘Therefore, man’s effective con- 
quest of the equatorial regions will be 
postponed until necessity drives him 
to the task. 
Population Capacity 
In discussing the numbers of the 
people who can be supported on the 
world’s resources, which we may call 
its population capacity, we are in fact 
studying the possibilities of the food 
supply. ‘There are three sets of con- 
ditions on which we may base esti- 
mates: 
(1) We may assume that the prin- 
cipal foods and the methods of pro- 
ducing them will remain much as they 
are today, and that the increase of 
supplies will only be that due to raising 
the standards of cultivation in back- 
ward areas, using improved strains of 
food plants and animals, and making 
full use of all the cultivable land. 
(2) We may make the additional 
assumption that man will, in the near 
future, overcome the difficulties of 
cultivation in the wet lands of the hot 
belt and add them to his area of 
cultivation. 
(3) We may guess at more or less 
