(4) Scanty Supply and Poor Quality of people think of tropical regions as the home of many animals. There live the dangerous carnivore such as the lion and tiger, and a host of herbivore such as the elephant, hippopotamus, gnu, and many antelopes. Never theless, domestic animals are scarce and of poor quality. The reason is that in tropical climates the more valuable domestic animals—the cow, sheep, and horse—are forced to live under conditions quite dif ferent from their optima, so that they cannot easily resist disease. Moreover, the frequent scarcity of food, forage, and the presence of innumerable insect pests like the tick and tsetse fly weaken them. Hence, the domestic animals are often too small and weak to be of great use as draught animals, and are too few in number to furnish the proteid needed by people whose diet is otherwise so starchy.
(5) Lack of Seasonal Stimulus.—Man's own qualities, quite as much as those of the plants and animals, tend to retard tropical agriculture and civilization. In the earlier stages of human evolution few stimuli are more potent than a long dry or cold season. Suppose that two groups of primitive people were alike, but one was placed in a mild, well-watered tropical region and the other in a region with a fairly severe winter. In the tropical region where food can be procured easily at all times, where clothing is not essential, and where anyone can make a simple shelter from the rain, the stupid and inactive people would have little trouble, but in the more severe climate they would be killed off because they would not have sense and energy enough to provide for the long winter. Such climatic selection helps to explain why tropical people have a racial inheritance which makes them less energetic, effi cient, and inventive than the races of more bracing climates.
(6) Health Within the Tropics.—(a) Poor Diet.—Tropical races are physically and mentally handicapped by poor health as well as by inheritance.
This arises in four impor tant ways, whose relative importance is estimated quite differently by different authorities: (a) from poor diet; (b) from the departure of the climate from the human optima; (c) from the ravages of disease due largely to insect pests and bacteria, and (d) from ignorance, superstition, and unhygienic and unsanitary practices. The coarse, bulky, starchy, diet causes many digestive disorders and other diseases. Beans and various kinds of pulse are indeed raised to supply the lack of proteid, but not in sufficient quantities. Many
tropical people have such a craving for meat that when they wish to honor a stranger they give him so much meat that he craves vegetables and fruit. Another cause of ill health is the monotony of the tropical diet. If people have rice, they often eat rice and almost nothing else; if they have millet or cassava, they eat millet or cassava.
(b) Departure from Climatic Optima. — A similar weakening of tropical people is due directly to the climate. The optima for different races appear to vary far less than do the climates in which men actually dwell. For example, the best temperature for Sicilians and Finns is apparently almost identical, and the best for Negroes in the United States appears to be 68° F., or only 4° F., higher than for whites. This seems to mean that practically all tropical people live permanently in a temperature higher than their optimum. This is much worse than living where the temperature is permanently too low, for in cold places people can create the right temperature by means of houses, fires, clothes, and exercises; whereas no one has yet found any practical means of overcom ing the heat. The fact that mental activity is probably most stimulated where the outdoor temperature averages about 40° F. makes the tropical heat still more harmful. When the depressing effect of constant monot ony and too much moisture is added to all this, it is not surprising that although tropical people sometimes work long and laboriously, they almost never show the zest and energy characteristic of northerners, and rarely do any deep thinking. With the exception of Mohammed no great man of the first rank is known to have been born and brought up within 25° of the equator, even Gautama, the founder of Buddhism, hav ing grown up in latitude 27° N. at the foot of the Himalayas.
(c) Effect of Tropical Diseases.—The unfavorable diet and climate of the tropics produce their worst effects through disease. People who are weakened by a poor diet or an unfavorable climate readily succumb to such organisms as the hookworm, which afflicts hundreds of millions of persons in warm and tropical climates. In Egypt half the laboring population is infected with hookworm, in the Malay States 60 per cent, British Honduras 70 per cent, the Philippines 15 to 75 per cent accord ing to locality, Sumatra and Java as high as 90 per cent in some regions, and so on for almost all tropical countries.