Popular Science Monthly/Volume 25/July 1884/Adaptation to Climate
|ADAPTATION TO CLIMATE.|
ANIMALS and plants are fitted by their organization to adapt themselves to many changes of place and vicissitudes of climate. Most of the domestic plants that are cultivated in the north originated in southern regions. The trees of the orange family were not cultivated in Italy in Pliny's time. The citron was not raised there with success till the third century; and lemons and oranges, which now grow in Southern Tyrol, not till later. The mulberry, which has now made its way to Norway, likewise did not flourish in Italy when Pliny wrote. Juicy peaches were not grown in Greece in the time of Aristotle, and even in Rhodes the blossoms only developed into a thin, woody fruit; but the peach-tree, bearing choice fruit, is now common through all France, and in the gardens of Central Germany. Chestnuts, originally at home only in warmer Asia, are now equally so in Italy and Western Germany. Some plants, notably the cereals, have enjoyed a very extensive diffusion in the course of centuries, and are now cultivated in nearly every part of the habitable earth. Our domestic animals, which mostly came from Asia, have gone with man to all the quarters of the world; and it is worthy of note that it is just those cereals and domestic animals that have proved themselves most useful to man, and are essential to civilized life, that preeminently possess the faculty of adapting themselves to all climates, and of producing the most diversified varieties.
The power of adaptation to climates appears to be most highly developed in man. He is less than any other being bound to any particular zone, and is further suited to the widest diffusion, because, confined to no especial food, he is, in the fullest sense of the word, omnivorous. He is, not only by the organization of his body, but especially by his mental power and his energetic will, fitted above all other creatures to accommodate himself to the most various influences that can affect him from without, and by continuous habitude to endure or make bearable the strangest conditions. He can live at the extreme limits at which organic life can exist, and can sustain a degree of cold at which quicksilver freezes. Thus, three Russians lived for seven years in Spitzbergen without suffering in health. Admiral Wrangell, while in the Chuckchee country in 1820, experienced a cold of nearly 50° below zero, while his men were as lively and happy as if it had been summer; and Parry and Franklin withstood a still greater cold. Man can also sustain an almost incredible degree of heat. The celebrated physician, Boerhaave, believed that no being breathing with lungs could live in an atmosphere having as high a temperature as that of the blood. According to this dictum, one ought to die at a temperature of 100°, but Banks enjoyed good health on the Senegal when the thermometer rose in his cabin to above 120° and 130°. Men live on the southwest coasts of Africa, and in other hot regions, where the heat of the sand under their feet reaches 140° or 150°. Men in deep mining-shafts and under diving-bells are able to support an atmospheric pressure of 30,000 kilogrammes as well as a pressure of only 8,000 kilogrammes on the highest mountains. Cassini thought that no animal could live at a greater height than 4,700 metres, or 15,000 feet; but there are several inhabited places situated at a still greater height, as, for instance, Gartok, in the Himalayas. Alexander von Humboldt ascended Chimborazo to a height of nearly 6,000 metres, or 19,286 feet, without suffering any harm. The pressure of the atmosphere is so light at such elevations that, as Humboldt was assured, wild animals when driven up to them bleed at the mouth and nose. Only the dog is able to follow man as far and as high as he can go; but this animal, too, loses his acute smell in Congo and Syria, and the power of barking in Surinam and at great heights; and the finer breeds of dogs can not long endure the conditions of a height of more than 3,760 metres, or 12,500 feet, while there are towns in the Andes at as great a height as 13,500 or 14,000 feet.
But there are regions in which even man perishes, to whatever race he may belong, and however well prepared he may be to resist their deadly influence. Among such regions is the Gaboon valley, in which even the negro is disabled. The inhabitants of that district are decidedly weaker in constitution, and have greatly diminished reproductive powers, and the women are considerably in excess. There are similar regions nearer the centers of civilization. The Tuscan Maremma is famous for its deadly air, and the swamps of Corsica are of like character. In France the ponds of the Dombes and the mouth-country of the Charente were, till recently, no less dangerous. Life in great cities also seems to exercise a special influence on reproduction. Boudin could not find any pure Parisians who could trace the residence of their ancestors in the city back for more than three generations. In Besançon the "old families" generally die out in not quite a hundred years, and are replaced by families from the country; and the same is, to a greater or less extent, the case in London, Berlin, and other large cities.
Has it been proved that on ships, where men are crowded together for months under conditions incompatible with health, particular disorders are developed, to which sailors may, indeed, gradually accustom themselves, but which are apt to mature into fatal maladies among people hitherto in perfect health? Can we, as Darwin suggests, ascribe to such circumstances the fearful mortality and the diminishing fruitfulness of the Polynesian races? Does the consumption which has become epidemic and hereditary in those islands belong to the diseases that have insinuated themselves there by the aid of European sailors? Neither the land nor the sky has changed since the Polynesian archipelagoes were discovered; yet the aboriginal population is diminishing at a really frightful rate, while its bastard offspring and the pure Europeans are increasing rapidly.
To what extent the more or less pronounced dangerousness of a locality is affected by normal conditions or by casual injurious influences is not always easy to estimate. The character of the soil, a higher or lower temperature, dryness, and moisture, are not all that determine the character of a country. We have evidence of this in the fact that the process of acclimatization is not equally easy in both hemispheres. The white races fare much better in the hot countries of the southern hemisphere than in the corresponding latitudes of the northern hemisphere. Between the thirtieth and thirty-fifth parallels of latitude lie Algiers and a part of the United States—regions in which the acclimatizing of Europeans is attended with great difficulties. In the southern hemisphere, the southern part of the Cape Colony and New South Wales lie between the same parallels, and in those countries white men thrive. French and English troops exhibit a rate of mortality eleven times as great in the northern as in the southern hemisphere—a striking difference, which appears to depend upon the greater frequency and intensity of miasmatic fevers. North of the equator these fevers reach in Europe to the fifty-ninth degree of latitude, while south of the equator they seldom extend beyond the tropic and usually do not reach it. Tahiti lies under the eighteenth degree of south latitude, and is free from fevers. French and English troops stationed in the southern hemisphere afford a mean of 1·6 per thousand sick with fever annually, while among those stationed in the northern hemisphere the proportion of fever-sick is 224 per thousand. Thus miasmatic fevers are two hundred times more frequent north of the equator than south of it, notwithstanding that there are extensive regions in South America and Australia covered with standing water and exposed to a burning sun. To this may be added that attacks of fever are much less severe in the southern hemisphere. Only light fevers prevail in the great lagoons of Corrientes; how much more dangerous are the fevers of the Pontine marshes, which are, nevertheless, very far from the equator! A European can live with much greater security against the contingency of fevers on the banks of the Parana, in South America, than on the banks of the Garigliano, in Italy.
There has been no lack of attempts and theories to explain these differences in localities that seem otherwise generally to stand under the same physical relations, but none of them have been successful. Yet it appears to be established that the greatest difficulties in the way of Europeans becoming acclimated in places where their business leads them to settle are due to the presence of swamp miasms. We know that a variety of conditions must combine to produce such miasms, and we know also that man is able to contend against them. It is possible for man to open a campaign against Nature wherever he goes, and to introduce conditions more favorable to his becoming acclimated. But he has so far not been able to bring a whole country immediately into a healthy condition; only time seems to be competent to bring such a work to completion, and, waiting its course, numerous victims have to be offered up.
The cultivation of the eucalyptus, a tree of remarkably quick growth, appears to be one of the most effective means now available for improving the condition of unhealthy localities. There are frequently tracts of limited extent in the most sickly regions where the process of acclimatization is relatively easy and secure. Such points should always be chosen by new settlers. The contrary has generally been the case. The beauty and fertility of the alluviums at the mouths of rivers, with the conveniences they offer to trade, have generally been tempting enough to determine the location of the settlement, regardless of its qualities with reference to health; and towns have been planted in such places in consideration of the apparent value of the money-investment, but in complete forgetfulness of the immense capital in human lives they are destined to swallow.—Translated for the Popular Science Monthly from Das Ausland.