Bible Encyclopedias
Acclimatization

Different Degrees of Climatal Adaptation in Animals and Plants

Plants differ greatly from animals in the closeness of their adaptation to meteorological conditions. Not only will most tropical plants refuse to live in a temperate climate, but many species are seriously injured by removal a few degrees of latitude beyond their natural limits. This is probably due to the fact, established by the experiments of A. C. Becquerel, that plants possess no proper temperature, but are wholly dependent on that of the surrounding medium.

Animals, expecially the higher forms, are much less sensitive to change of temperature, as shown by the extensive range from north to south of many species. Thus, the tiger ranges from the equator to northern Asia as far as the river Amur, and to the isothermal of 32° Fahr. The mountain sparrow (Passer montana) is abundant in Java and Singapore in a uniform equatorial climate, and also inhabits Britain and a considerable portion of northern Europe. It is true that most terrestrial animals are restricted to countries not possessing a great range of temperature or very diversified climates, but there is reason to believe that this is due to quite a different set of causes, such as the presence of enemies or deficiency of appropriate food. When supplied with food and partially protected from enemies, they often show a wonderful capacity of enduring climates very different from that in which they originally flourished. Thus, the horse and the domestic fowl, both natives of very warm countries, flourish without special protection in almost every inhabited portion of the globe. The parrot tribe form one of the most pre-eminently tropical groups of birds, only a few species extending into the warmer temperate regions; yet even the most exclusively tropical genera are by no means delicate birds as regards climate. In the Annals and Magazine of Natural History for 1868 (p. 381) is a most interesting account, by Charles Buxton, of the naturalization of parrots at Northreps Hall, Norfolk. A considerable number of African and Amazonian parrots, Bengal parroquets, four species of white and rose crested cockatoos, and two species of crimson lories, remained at large for many years. Several of these birds bred, and they almost all lived in the woods the whole year through, refusing to take shelter in a house constructed for their use. Even when the thermometer fell 6° below zero, all appeared in good spirits and vigorous health. Some of these birds have lived thus exposed for many years, enduring the English cold easterly winds, rain, hail and snow, all through the winter - a marvellous contrast to the equable equatorial temperature (hardly ever less than 70°) to which many of them had been accustomed for the first year or years of their existence. Similarly the recent experience of zoological gardens, particularly in the case of parrots and monkeys, shows that, excluding draughts, exposure to changes of temperature without artificial heat is markedly beneficial as compared with the older method of strict protection from cold.

Hardly any group of Mammalia is more exclusively tropical than the Quadrumana, yet, if other conditions are favourable, some of them can withstand a considerable degree of cold. Semnopithecus schistaceus was found by Captain Hutton at an elevation of 11,000 feet in the Himalayas, leaping actively among fir-trees whose branches were laden with snow-wreaths. In Abyssinia a troop of dog-faced baboons was observed by W. T. Blanford at 9000 feet above the sea. We may therefore conclude that the restriction of the monkey tribe to warm latitudes is probably determined by other causes than temperature alone.

Similar indications are given by the fact of closely allied species inhabiting very extreme climates. The recently extinct Siberian mammoth and woolly rhinoceros were closely allied to species now inhabiting tropical regions exclusively. Wolves and foxes are found alike in the coldest and hottest parts of the earth, as are closely allied species of falcons, owls, sparrows and numerous genera of waders and aquatic birds.

A consideration of these and many analogous facts might induce us to suppose that, among the higher animals at least, there is little constitutional adaptation to climate, and that in their case acclimatization is not required. But there are numerous examples of domestic animals which show that such adaptation does exist in other cases. The yak of Thibet cannot long survive in the plains ofIndia, or even on the hills below a certain altitude; and that this is due to climate, and not to the increased density of the atmosphere, is shown by the fact that the same animal appears to thrive well in Europe, and even breeds there readily. The Newfoundland dog will not live in India, and the Spanish breed of fowls in this country suffer more from frost than most others. When we get lower in the scale the adaptation is often more marked. Snakes, which are so abundant in warm countries, diminish rapidly as we go north, and wholly cease at lat. 62°. Most insects are also very susceptible to cold, and seem to be adapted to very narrow limits of temperature.

From the foregoing facts and observations we may conclude, firstly, that some plants and many animals are not constitutionally adapted to the climate of their native country only, but are capable of enduring and flourishing under a more or less extensive range of temperature and other climatic conditions; and, secondly, that most plants and some animals are, more or less closely, adapted to climates similar to those of their native habitats. In order to domesticate or naturalize the former class in countries not extremely differing from that from which the species was brought, it will not be necessary to acclimatize, in the strict sense of the word. In the case of the latter class, however, acclimatization is a necessary preliminary to naturalization, and in many cases to useful domestication, and we have therefore to inquire whether it is possible.

Acclimatization by Individual Adaptation

It is evident that acclimatization may occur (if it occurs at all) in two ways, either by modifying the constitution of the individual submitted to the new conditions, or by the production of offspring which may be better adapted to those conditions than their parents. The alteration of the constitution of individuals in this direction is not easy to detect, and its possibility has been denied by many writers. C. Darwin believed, however, that there were indications that it occasionally occurred in plants, where it can be best observed, owing to the circumstance that so many plants are propagated by cuttings or buds, which really continue the existence of the same individual almost indefinitely. He adduced the example of vines taken to the West Indies from Madeira, which have been found to succeed better than those taken directly from France. But in most cases habit, however prolonged, appears to have little effect on the constitution of the individual, and the fact has no doubt led to the opinion that acclimatization is impossible. There is indeed little or no evidence to show that any animal to which a new climate is at first prejudicial can be so acclimatized by habit that, after subjection to it for a few or many seasons, it may live as healthily and with as little care as in its native country; yet we may, on general principles, believe that under proper conditions such an acclimatization would take place.

Acclimatization by Variation

A mass of evidence exists showing that variations of every conceivable kind occur among the offspring of all plants and animals, and that, in particular, constitutional variations are by no means uncommon. Among cultivated plants, for example, hardier and more tender varieties often arise. The following cases are given by C. Darwin: - Among the numerous fruit-trees raised in North America some are well adapted to the climate of the northern States and Canada, while others only succeed well in the southern States. Adaptation of this kind is sometimes very close, so that, for example, few English varieties of wheat will thrive in Scotland. Seed-wheat from India produced a miserable crop when planted by the Rev. M. J. Berkeley on land which would have produced a good crop of English wheat. Conversely, French wheat taken to the West Indies produced only barren spikes, while native wheat by its side yielded an enormous harvest. Tobacco in Sweden, raised from home-grown seed, ripens its seeds a month earlier than plants grown from foreign seed. In Italy, as long as orange trees were propagated by grafts, they were tender; but after many of the trees were destroyed by the severe frosts of 1709 and 1763, plants were raised from seed, and these were found to be hardier and more productive than the former kinds. Where plants are raised from seed in large quantities, varieties always occur differing in constitution, as well as others differing in form or colour; but the former cannot be perceived by us unless marked out by their behaviour under exceptional conditions, as in the following cases. After the severe winter of 1860-1861 it was observed that in a large bed of araucarias some plants stood quite unhurt among numbers killed around them. In C. Darwin's garden two rows of scarlet runners were entirely killed by frost, except three plants, which had not even the tips of their leaves browned. A very excellent example is to be found in Chinese history, according to E. R. Huc, who, in his L' Empire chinois (tom. ii. p. 359), gives the following extract from the Memoirs of the Emperor Khang: - " On the 1st day of the 6th moon I was walking in some fields where rice had been sown to be ready for the harvest in the 9th moon. I observed by chance a stalk of rice which was already in ear. It was higher than all the rest, and was ripe enough to be gathered. I ordered it to be brought to me. The grain was very fine and well grown, which gave me the idea to keep it for a trial, and see if the following year it would preserve its precocity. It did so.

All the stalks which came from it showed ear before the usual time, and were ripe in the 6th moon. Each year has multiplied the produce of the preceding, and for thirty years it is this rice which has been served at my table. The grain is elongate and of a reddish colour, but it has a sweet smell and very pleasant taste. It is called V u-mi, Imperial rice, because it was first cultivated in my gardens. It is the only sort which can ripen north of the great wall, where the winter ends late and begins very early; but in the southern provinces, where the climate is milder and the land more fertile, two harvests a year may be easily obtained, and it is for me a sweet reflection to have procured this advantage for my people." Huc adds his testimony that this kind of rice flourishes in Manchuria, where no other will grow. We have here, therefore, a perfect example of acclimatization by means of a spontaneous constitutional variation.

That this kind of adaptation may be carried on step by step to more and more extreme climates is illustrated by the following examples. Sweet-peas raised in Calcutta from seed imported from England rarely blossom, and never yield seed; plants from French seed flower better, but are still sterile; but those raised from Darjeeling seed (originally imported from England) both flower and seed profusely. The peach is believed to have been tender, and to have ripened its fruit with difficulty, when first introduced into Greece; so that (as Darwin observes) in travelling northward during two thousand years it must have become much hardier. Sir J. Hooker ascertained the average vertical range of flowering plants in the Himalayas to be 4000 ft., while in some cases it extended to 8000 ft. The same species can thus endure a great difference of temperature; but the important fact is, that the individuals have become acclimatized to the altitude at which they grow, so that seeds gathered near the upper limit of the range of a species will be more hardy than those gathered near the lower limit. This was proved by Hooker to be the case with Himalayan conifers and rhododendrons, raised in Britain from seed gathered at different altitudes.

Among animals exactly analogous facts occur. When geese were first introduced into Bogota they laid few eggs at long intervals, and few of the young survived. By degrees the fecundity improved, and in about twenty years became equal to what it is in Europe. The same author tells us that, according to Garcilaso, when fowls were first introduced into Peru they were not fertile, whereas now they are as much so as in Europe. C. Darwin adduced the following examples. Merino sheep bred at the Cape of Good Hope have been found far better adapted for India than those imported from England; and while the Chinese variety of the Ailanthus silk-moth is quite hardy, the variety found in Bengal will only flourish in warm latitudes. C. Darwin also called attention to the circumstance that writers of agricultural works generally recommend that animals should be removed from one district to another as little as possible. This advice occurs even in classical and Chinese agricultural books as well as in those of our own day, and proves that the close adaptation of each variety or breed to the country in which it originated has always been recognized.

Constitutional Adaptation often accompanied by External Modification

Although in some cases no perceptible alteration of form or structure occurs when constitutional adaptation to climate has taken place, in others it is very marked. C. Darwin collected a large number of cases in his Animals and Plants under Domestication. In his Contributions to the Theory of Natural Selection (p. 167), A. R. Wallace has recorded cases of simultaneous variation among insects, apparently due to climate or other strictly local causes. He found that the butterflies of the family Papilionidae, and some others, became similarly modified in different islands and groups of islands. Thus, the species inhabiting Sumatra, Java and Borneo are almost always much smaller than the closely allied species of Celebes and the Moluccas; the species or varieties of the small island of Amboyna are larger than the same species or closely allied forms inhabiting the surrounding islands; the species found in Celebes possess a peculiar form of wing, quite distinct from that of the same or closely allied species of adjacent islands; and, lastly, numerous species which have tailed wings in India and the western islands of the Archipelago, gradually lose the tail as we proceed eastward to New Guinea and the Pacific.

Many of these curious modifications may, it is true, be due to other causes than climate only, but they serve to show how powerfully and mysteriously local conditions affect the form and structure of both plants and animals; and they render it probable that changes of constitution are also continually produced, although we have, in the majority of cases, no means of detecting them. It is also impossible to determine how far the effects described are produced by spontaneous favourable variations or by the direct action of local conditions; but it is probable that in every case both causes are concerned, although in constantly varying proportions.

Selection and Survival of the Fittest as Agents in Naturalization.

We may now take it as an established fact that varieties of animals and plants occur, both in domesticity and in a state of nature, which are better or worse adapted to special climates. There is no positive evidence that the influence of new climatal conditions on the parents has any tendency to produce variations in the offspring better adapted to such conditions. Neither does it appear that this class of variations are very frequent. It is, however, certain that whenever any animal or plant is largely propagated constitutional variations will arise, and some of these will be better adapted than others to the climatal and other conditions of the locality. In a state of nature, every recurring severe winter or otherwise unfavourable season weeds out those individuals of tender constitution or imperfect structure which may have got on very well during favourable years, and it is thus that the adaptation of the species to the climate in which it has to exist is kept up. Under domestication the same thing occurs by what C. Darwin has termed "unconscious selection." Each cultivator seeks out the kinds of plants best suited to his soil and climate and rejects those which are tender or otherwise unsuitable. The farmer breeds from such of his stock as he finds to thrive best with him, and gets rid of those which suffer from cold, damp or disease. A more or less close adaptation to local conditions is thus brought about, and breeds or races are produced which are sometimes liable to deterioration on removal even to a short distance in the same country, as in numerous cases quoted by C. Darwin (Animals and Plants under Domestication). The Method of Acclimatization. - Taking into consideration the foregoing facts and illustrations, it may be considered as proved - ist, That habit has little (though it appears to have some) definite effect in adapting the constitution of animals to a new climate; but that it has a decided, though still slight, influence in plants when, by the process of propagation by buds, shoots or grafts, the individual can be kept under its influence for long periods; and, That great and sudden changes of climate often check reproduction even when the health of the individuals does not appear to suffer. In order, therefore, to have the best chance of acclimatizing any animal or plant in a climate very dissimilar from that of its native country, and in which it has been proved that the species in question cannot live and maintain itself without acclimatization, we must adopt some such plan as the following: i. We must transport as large a number as possible of adult healthy individuals to some intermediate station, and increase them as much as possible for some years. Favourable variations of constitution will soon show themselves, and these should be carefully selected to breed from, the tender and unhealthy individuals being rigidly eliminated.

2. As soon as the stock has been kept a sufficient time to pass through all the ordinary extremes of climate, a number of the hardiest may be removed to the more remote station, and the same process gone through, giving protection if necessary while the stock is being increased, but as soon as a large number of healthy individuals are produced, subjecting them to all the vicissitudes of the climate.

It can hardly be doubted that in most cases this plan would succeed. It has been recommended by C. Darwin, and at one of the early meetings of the Societe Zoologique d'Acclimatation, at Paris, Isodore Geoffroy St Hilaire insisted that it was the only method by which acclimatization was possible. But in looking through the long series of volumes of Reports published by this society, there is no sign that any systematic attempt at acclimatization has even once been made. A number of foreign animals have been introduced, and more or less domesticated, and some useful exotics have been cultivated for the purpose of testing their applicability to French agriculture or horticulture; but neither in the case of animals nor of plants has there been any systematic effort to modify the constitution of the species, by breeding largely and selecting the favourable variations that appeared. Take the case of the Eucalyptus globulus as an example. This is a Tasmanian gum-tree of very rapid growth and great beauty, which will thrive in the extreme south of France. In the Bulletin of the society a large number of attempts to introduce this tree into general cultivation in other parts of France are recorded in detail, with the failure of almost all of them. But no precautions such as those above indicated appear to have been taken in any of these experiments; and we have no intimation that either the society or any of its members are making systematic efforts to acclimatize the tree. The first step would be, to obtain seed from healthy trees growing in the coldest climate and at the greatest altitude in its native country, sowing these very largely, and in a variety of soils and situations, in a part of France where the climate is somewhat but not much more extreme. It is almost a certainty that a number of trees would be found to be quite hardy. As soon as these produced seed, it should be sown in the same district and farther north in a climate a little more severe. After an exceptionally cold season, seed should be collected from the trees that suffered least, and should be sown in various districts all over France. By such a process there can be hardly any doubt that the tree would be thoroughly acclimatized in any part of France, and in many other countries of central Europe; and more good would be effected by one well-directed effort of this kind than by hundreds of experiments with individual animals and plants, which only serve to show us which are the species that do not require to be acclimatized. Acclimatization of Man. - On this subject we have, unfortunately, very little direct or accurate information. The general laws of heredity and variation have been proved to apply to man as well as to animals and plants; and numerous facts in the distribution of races show that man must, in remote ages at least, have been capable of constitutional adaptation to climate. If the human race constitutes a single species, then the mere fact that man now inhabits every region, and is in each case constitutionally adapted to the climate, proves that acclimatization has occurred. But we have the same phenomenon in single varieties of man, such as the American, which inhabits alike the frozen wastes of Hudson's Bay and Tierra del Fuego, and the hottest regions of the tropics, - the low equatorial valleys and the lofty plateaux of the Andes. No doubt a sudden transference to an extreme climate is often prejudicial to man, as it is to most animals and plants; but there is every reason to believe that, if the migration occurs step by step, man can be acclimatized to almost any part of the earth's surface in comparatively few generations. Some eminent writers have denied this. Sir Ranald Martin, from a consideration of the effects of the climate of India on Europeans and their offspring, believed that there is no such thing as acclimatization. Dr Hunt, in a report to the British Association in 1861, argued that "time is no agent," and - "if there is no sign of acclimatization in one generation, there is no such process." But he entirely ignored the effect of � favourable variations, as well as the direct influence of climate acting on the organization from infancy.

Professor Theodor Waitz, in his Introduction to Anthropology, adduced many examples of the comparatively rapid constitutional adaptation of man to new climatic conditions. Negroes, for example,who have been for three or four generations acclimatized in North America, on returning to Africa become subject to the same local diseases as other unacclimatized individuals. He well remarked that the debility and sickening of Europeans in many tropical countries are wrongly ascribed to the climate, but are rather the consequences of indolence, sensual gratification and an irregular mode of life. Thus the English, who cannot give up animal food and spirituous liquors, are less able to sustain the heat of the tropics than the more sober Spaniards and Portuguese. The excessive mortality of European troops in India, and the delicacy of the children of European parents, do not affect the real question of acclimatization under proper conditions. They only show that acclimatization is in most cases necessary, not that it cannot take place. The best examples of partial or complete acclimatization are to be found where European races have permanently settled in the tropics, and have maintained themselves for several generations. There are, however, two sources of inaccuracy to be guarded against, and these are made the most of by the writers above referred to, and are supposed altogether to invalidate results which are otherwise opposed to their views. In the first place, we have the possibility of a mixture of native blood having occurred; in the second, there have almost always been a succession of immigrants from the parent country, who continually intermingle with thefamilies of the early settlers. It is maintained that one or other of these mixtures is absolutely necessary to enable Europeans to continue long to flourish in the tropics.

There are, however, certain cases in which the sources of error above mentioned are reduced to a minimum, and cannot seriously affect the results; such as those of the Jews, the Dutch at the Cape of Good Hope and in the Moluccas, and the Spaniards in South America.

The Jews are a good example of acclimatization, because they have been established for many centuries in climates very different from that of their native land; they keep themselves almost wholly free from intermixture with the people around them; and they are often so populous in a country that the intermixture with Jewish immigrants from other lands cannot seriously affect the local purity of the race. They have, for instance, attained a population of millions in such severe climates as Poland and Russia; in the towns of Algeria they have succeeded so conspicuously as to bring about an outburst of anti-semitism; and in Cochin-China and Aden they succeed in rearing children and forming permanent communities.

In some of the hottest parts of South America Europeans are perfectly acclimatized, and where the race is kept pure it seems to be even improved. Some very valuable notes on this subject were furnished to the present writer by the well-known botanist, Richard Spruce, who resided many years in South America, but who was prevented by ill-health from publishing his researches (see A. R. Wallace, Notes of a Botanist, 1908). As a careful, judicious and accurate observer, both of man and nature, he had few superiors. He says: The white inhabitants of Guayaquil (lat. 2° 13' S.) are kept pure by careful selection. The slightest tincture of red or black blood bars entry into any of the old families who are descendants of Spaniards from the Provincias Vascongadas or those bordering the Bay of Biscay, where the morals are perhaps the purest (as regards the intercourse of the sexes) of any in Europe, and where for a girl, even of the poorest class, to have a child before marriage is the rarest thing possible. The consequence of this careful breeding is, that the women of Guayaquil are considered (and justly) the finest along the whole Pacific coast. They are often tall, sometimes very handsome, decidedly healthy, although pale, and assuredly prolific enough. Their sons are big, stout men, but when they lead inactive lives are apt to become fat and sluggish. Those of them, however, who have farms in the savannahs and are accustomed to take long rides in all weathers, and those whose trade obliges them to take frequent journeys in the mountainous interior, or even to Europe and North America, are often as active and as little burdened with superfluous flesh as a Scotch farmer.

The oldest Christian town in Peru is Piura (lat. 5° S.), which was founded by Pizarro himself. The climate is very hot, especially in the three or four months following the southern solstice. In March 1843 the temperature only once fell as low as 83° during the whole month, the usual lowest night temperature being 85°. Yet people of all colours find it very healthy, and the whites are very prolific. I resided in the town itself nine months, and in the neighbourhood seven months more. The population (in 1863-1864)wasabout 10,000, of which not only a considerable proportion was white, but was mostly descended from the first emigrants after the conquest. Purity of descent was not, however, quite so strictly maintained as at Guayaquil. The military adventurers, who have often risen to high or even supreme rank in Peru, have not seldom been of mixed race, and fear or favour has often availed to procure them an alliance with the oldest and purest-blooded families.

These instances, so well stated by Spruce, seem to demonstrate the complete acclimatization of Spaniards in some of the hottest parts of South America. Although we have here nothing to do with mixed races, yet the want of fertility in these has been often taken to be a fact inherent in the mongrel race, and has been also sometimes held to prove that neither the European nor his half-bred offspring can maintain themselves in the tropics. The following observation is therefore of interest: At Guayaquil for a lady of good family - married or unmarried - to be of loose morals is so uncommon, that when it does happen it is felt as a calamity by the whole community. But here, and perhaps in most other towns in South America, a poor girl of mixed race - especially if good-looking - rarely thinks of marrying one of her own class until she has - as the Brazilians say - "approveitada de sua mocidade" (made the most of her youth) in receiving presents from gentlemen. If she thus bring a good dowry to her husband, he does not care to inquire, or is not sensitive, about the mode in which it was acquired. The consequence of this indiscriminate sexual intercourse, especially if much prolonged, is to diminish, in some cases to paralyse, the fertility of the female. And as among people of mixed race it is almost universal, the population of these must fall off both in numbers and quality.

The following example of divergent acclimatization of the same race to hot and cold zones is very interesting, and will conclude our extracts from Spruce's valuable notes: One of the most singular cases connected with this subject that have fallen under my own observation, is the difficulty, or apparent impossibility, of acclimatizing the Red Indian in a certain zone of the Andes. Any person who has compared the physical characters of the native races of South America must be convinced that these have all originated in a common stirps. Many local differences exist, but none capable of invalidating this conclusion. The warmth yet shade-loving Indian of the Amazon; the Indian of the hot, dry and treeless coasts of Peru and Guayaquil, who exposes his bare head to the sun with as much zest as an African negro; the Indian of the Andes, for whom no cold seems too great, who goes constantly barelegged and often bare-headed, through whose rude straw hut the piercing wind of the paramos sweeps and chills the white man to the very bones; - all these, in the colour and texture of the skin, the hair and other important features, are plainly of one and the same race.

Now there is a zone of the equatorial Andes, ranging between about 4000 and 6000 feet altitude, where the very best flavoured coffee is grown, where cane is less luxuriant but more saccharine than in the plains, and which is therefore very desirable to cultivate, but where the red man sickens and dies. Indians taken down from the sierra get ague and dysentery. Those of the plains find the temperature chilly, and are stricken down with influenza and pains in the limbs. I have seen the difficulty experienced in getting farms cultivated in this zone, on both sides of the Cordillera. The permanent residents are generally limited to the major-domo and his family; and in the dry season labourers are hired, of any colour that can be obtained - some from the low country, others from the highlands - for three, four, or five months, who gather in and grind the cane, and plant for the harvest of the following year; but the staff of resident Indian labourers, such as exists in the farms of the sierra, cannot be kept up in the Yungas, as these half-warm valleys are called. White men, who take proper precautions, and are not chronically soaked with cane-spirit, stand the climate perfectly, but the creole whites are still too much caballeros to devote themselves to agricultural work.

In what is now the republic of Ecuador, the only peopled portions are the central valley, between the two ridges of the Andes - height 7000 to 12,000 feet - and the hot plain at their western base; nor do the wooded slopes appear to have been inhabited, except by scattered savage hordes, even in the time of the Incas. The Indians of the highlands are the descendants of others who have inhabited that region exclusively for untold ages; and a similar affirmation may be made of the Indians of the plain. Now, there is little doubt that the progenitors of both these sections came from a temperate region (in North America); so that here we have one moiety acclimatized to endure extreme heat, and the other extreme cold; and at this day exposure of either to the opposite extreme (or even, as we have seen, to the climate of an intermediate zone) is always pernicious and often fatal. But if this great difference has been brought about in the red man, might not the same have happened to the white man? Plainly it might, time being given; for one cannot doubt that the inherent adaptability is the same in both, or (if not) that the white man possesses it in a higher degree.

The observations of Spruce are of themselves almost conclusive as to the possibility of Europeans becoming acclimatized in the tropics; and if it is objected that this evidence applies only to the dark-haired southern races, we are fortunately able to point to facts, almost equally well authenticated and conclusive, in the case of one of the typical Germanic races. In South Africa the Dutch have been settled and nearly isolated for over 200 years, and have kept themselves almost or quite free from native intermixture. They are still preponderatingly fair in complexion, while physically they are tall and strong. They marry young and have large families. The population, according to a census taken in 1798, was under 22,000. In 1865 it was near 182,000, the majority being of "Dutch, German or French origin, mostly descendants of original settlers." In more recent times, the conditions have been so greatly changed by immigration, that the later statistics cease to have a definite meaning with regard to acclimatization. We have here a population which doubled itself every twenty-two years; and the greater part of this rapid increase must certainly be due to the old European immigrants. In the Moluccas, where the Dutch have had settlements for 250 years, some of the inhabitants trace their descent to early immigrants; and these, as well as most of the people of Dutch descent in the east, are quite as fair as their European ancestors, enjoy excellent health, and are very prolific. But the Dutch accommodate themselves admirably to a tropical climate, doing much of their work early in the morning, dressing very lightly, and living a quiet, temperate and cheerful life. They also pay great attention to drainage and general cleanliness. In addition to these examples, it is obvious that the rapid increase of English-speaking populations in the United States and in Australia is far greater than can be explained by immigration, and shows two conspicuous examples of acclimatization.

On the whole, we seem justified in concluding that, under favourable conditions, and with a proper adaptation of means to the end in view, man may become acclimatized with at least as much certainty and rapidity (counting by generations rather than by years) as any of the lower animals. The greatest difficulty in his way is not temperature, but the presence of parasitic diseases to resist which his body has not been prepared, and modern knowledge is rapidly defining these dangers and the modes of avoiding them. (A. R. W.) Appendix The task of collecting information as to animals which have become permanently naturalized away from their native haunts is anything but easy, as few regular records have been kept by acclimatizers. Moreover, recorders of local fauna have been almost unanimous in ignoring the introduced forms, except when they have had occasion to comment on the effects, real or supposed, of these immigrants on aboriginal faunas.

Mammals

It is unnecessary here to dwell upon the worldwide distribution of the two rats Mus rattus and M. decumanus, and of the house-mouse M. musculus; their introduction has always been involuntary. Similarly nearly all our domestic mammals except the sheep have become feral somewhere or other, whether by intentional liberation or by escape; but the smaller ones more than the larger, such as pigs, goats, dogs and cats. This has been especially the case in Hawaii and New Zealand; in America, Australia and Hawaii, horses and cattle are also feral. Feral pigs are numerous in New Zealand.

The domestic Indian buffalo (Bos bubalus) exists as a wild animal in North Australia; it is very liable to revert to a wild state, being little altered from its still-existing wild ancestor.

A more curious case is that of the one-humped camel (Camelus dromedarius), a beast only known in domestication, and that in arid countries; yet a number of these have become feral in the Spanish marshes, where they wade about like quadrupedal flamingoes.

The red deer (Cervus elaphus) is now widely distributed as a wild animal over New Zealand, where also the fallow-deer (C. dama) and the Indian sambar (C. aristotelis or unicolor) have been introduced locally. The sambar, or one or other of its subspecies, has also been naturalized in Mauritius, and in the Marianne Islands in the open Pacific.

The wide introduction of the rabbit, as a wild animal, is well known. Amounting to a serious pest in Australasian colonies, it is also established in the Falklands and Kerguelen; its presence in much of Europe is attributed to early acclimatization, as it seems anciently to have been confined to the Iberian peninsula.

The hare has been established in New Zealand and Barbadoes. Few other rodents have been designedly naturalized, but the North American grey squirrel (Sciurus cinereus) appears to be established as a wild animal in Woburn Park, Bedfordshire, England, and may probably spread thence.

To check the increase of the rabbit, stoats, weasels and polecats (the last in the form of the domesticated ferret) were introduced into New Zealand on a very large scale in the last quarter of the 19th century. They have spread widely, and have not confined their depredations to the rabbits, so that the indigenous flightless birds have suffered largely.

Another carnivore of very similar habits, the Indian mongoose (Herpestus griseus or H. mungo), has been naturalized in Jamaica, whence it has been carried to other West Indian Islands, and in the Hawaiian group. It has also been tried, but unsuccessfully, in Australia. The first introduction into Jamaica took place in 1872, and ten years later the animal was credited with saving many thousands of pounds annually by its destruction of rats. But before an equal space of time had further elapsed, it had itself become a pest; the most recent information, however, is to the effect that its numbers are now on the decline, and that the disturbed faunal equilibrium is being readjusted.

The civets, being celebrated for their odoriferous secretion, are likely animals to have been naturalized. W. T. Blanford (Fauna of British India, " Mammals") thinks that the presence of the Indian form, Viverricula malaccensis, in Socotra, the Comoro Islands and Madagascar is due to the assistance of man.

The common fox of Europe has been introduced into Australia, where it is destructive to the native fauna and to lambs. Among primates, a Ceylonese monkey (Macacus pileatus) has been naturalized in Mauritius for centuries, the circumstances of introduction being unknown.

The common Australian "opossum" or phalanger (Trichosurus vulpecula) has been naturalized in New Zealand, although very destructive to fruit trees; the value of its fur being probably the motive. It is said that the pelage of the New Zealand specimens is superior, as might be expected from the colder climate.

Birds

The introduction of mammals has been largely influenced by economic conditions, when, indeed, it was not absolutely accidental and unavoidable; but in the case of birds it has been more gratuitous, so to speak, in many cases, and hence is looked upon with especial dislike by naturalists. The domestic birds have comparatively seldom become feral, doubtless, as C. Darwin points out, from the reduction of their powers of flight in many cases. The guinea-fowl, however, has long been in this condition in Jamaica and St Helena, and the fowl in Hawaii and other Polynesian islands. The pheasant has been naturalized in the United States, New Zealand, Hawaii and St Helena. Its naturalization in western Europe is very ancient, but the race supposed to have been introduced by the Romans (Phasianus colchicus) has been much modified within the last century or two by the introduction of the ring-necked Chinese form (P. torquatus), which produces fertile hybrids with the old breed. Thus those acclimatized were usually, no doubt, of mixed blood, and further introductions of pure Chinese stock have tended to make the latter the dominant form, at any rate in the United States (where it is erroneously called Mongolian') and in New Zealand. In Hawaii and St Helena the ring-neck appears to have been the only pheasant introduced pure, but in the former the Japanese race (P. versicolor) is also naturalized.

1 The true Mongolian pheasant (P. mongolicus), a very different bird, has recently been introduced into England.

The golden pheasant (Chrysolophus pictus) is locally established in the United States, as appear to be other pheasants of less common species. The Reeves' pheasant (P. reevesi) is at large on some English estates. Of the partridges, the continental red-leg (Caccabis rufa) is established in England, and its ally, the Asiatic chukore (C. chukar), in St Helena, as is the Californian quail (Lophortyx californica) in New Zealand and Hawaii. The latter, however, though thriving as an aviary bird, has failed at large in England, as did the bob-white (Onyx virginianus) both there and in New Zealand.

The desirable character of the grouse as game-birds has led to many attempts at their acclimatization, but usually these have been unsuccessful; the red grouse (Lagopus scoticus), however, the only endemic British bird, is naturalized in some parts of Europe.

Of waterfowl, the Canada goose (Branta canadensis) is naturalized to a small extent in Britain, and also, to a less degree, the Egyptian goose (Chenalopex aegyptiacus); the latter bird also occurs wild in New Zealand. The modern presence of the black swan of Australia (Chenopis atrata) in New Zealand appears to be due to a natural irruption of the species about half a century ago as much as to acclimatization by man, if not more so.

Birds of prey are, unjustly enough, regarded with so little favour that few attempts have been made to naturalize them; the continental little owl (Athene noctua), however, has for some time been well established in England, where it has hardly, if ever, appeared naturally.

Pigeons have been very little naturalized; the tame bird has become feral locally in various countries, and the Chinese turtledove (Turtur chinensis) is established in Hawaii, as is the small East Indian zebra dove (Geopelia striata) in the Seychelles, and the allied Australian (G. tranquilla) in St Helena. There has also been very little naturalization of parrots, but the rosella parrakeet of Australia (Platycercus eximius) is being propagated by escaped captives in the north island of New Zealand, and its ally the mealy rosella (P. pallidiceps) is locally wild in Hawaii, the stock in this case having descended from a single pair intentionally liberated. Attempts to naturalize that well-known Australian grass-parrakeet the budgerigar (Melopsittacus undulatus) in England have so far proved abortive, and none of the species experimented with in Norfolk and Bedfordshire effected a settlement. The greyheaded love-bird (Agapornis Cana) of Madagascar is established in the Seychelles. Some of the passerine birds have been the most widely distributed, especially the house-sparrow (Passer domesticus), which is now an integral, and very troublesome, part of the fauna in the Australasian States and in North America. It is, in fact, as notorious an example of over-successful acclimatization as the rabbit, but in Hutton and Drummond's recent work on the New Zealand animals (London, 1905) it is not regarded in this light, considering that some very common exotic birds were needed to keep down the insects, which it certainly did. Even in the United States also, it has been found a useful destroyer of weed-seeds. The house-sparrow is also feral in Argentina, some of the West Indian islands, Hawaii and the Andamans.

The allied tree-sparrow (P. montanus) has been locally naturalized in the United States; it is a more desirable bird, being less prolific and pugnacious, but it is expelled from towns by the house-sparrow.

The so-called Java sparrow (Munia oryzivora), although a destructive bird to rice, has been widely distributed by accident or design, and is now found in several East Indian islands besides Java, in south China, St Helena, India, Zanzibar and the east African coast. An allied but much smaller weaver-finch, a form of the spice-bird (Munia nisoria punctata), is introduced and well distributed over the Hawaiian islands. The little rooibek of South Africa (Estrilda astrild) has been so long and well established in St Helena that it is known in the bird trade as the St Helena waxbill, and the brilliant scarlet weaver of Madagascar (Foudia madagascariensis) inhabits as an imported bird Mauritius, the Seychelles and even the remote Chagos Islands.

Returning to the true finches, the only one which can compete with the house-sparrow in the extent of its distribution by man is the goldfinch (Carduelis carduelis), now established all over New Zealand, as well as in Australia, the United States and Jamaica. It bears a good character, and is one of the marked successes of naturalization. The redpoll (Acanthis linaria), chaffinch (Fringilla coelebs) and greenfinch (Chloris chloris) are established in New Zealand, the last named being a pest there, as is also the cirl-bunting (Emberiza cirlus) - the yellow-hammer (E. citrinella) being perhaps confused with this also.

Among starlings, the Indian mynah (generally the house mynah, Acridotheres tristis, but some other species seem to have been confused with this) has been naturalized in the Andamans, Seychelles, Reunion, Australia, Hawaii and parts of New Zealand. Its alleged destructiveness to the Hawaiian avifauna seems open to doubt.

The European starling (Sturnus vulgaris) is naturalized in New Zealand, Australia and to some extent in the United States. Thrushes have not been widely introduced, but the song-thrush and blackbird (Turdus musicus and Merula merula) are common in New Zealand; attempts were made, but unsuccessfully, to establish the latter in the United States. The so-called hedge-sparrow (Accentor modularis), really a member of this group, is one of the successful introductions into New Zealand. The robin (Erithacus rubecula) failed there.

Rooks (Corvus frugilegus) and the Australian "magpie" or piping crow (Gymnorhina) are to be found in New Zealand, but only locally, especially the former.

==Reptiles and Amphibians==Very little naturalization has been effected, or indeed apparently attempted, in regard to these groups, but the occurrence of the edible frog of the continent of Europe (Rana esculents) as an introduced animal in certain British localities is well known. An Australian tree-frog (Hyla peronii) is naturalized in many parts of the north island of New Zealand.

==Fish==The instances of naturalization in this class are few, but important. The common carp (Cyprinus carpio), originally a Chinese fish, has for centuries been acclimatized in Europe, where indeed it is in places a true domestic creature, with definite variations. It is, however, quite feral also, and has been introduced into North America.

The Prussian carp (Carassius vulgaris) is established in New Zealand, and the nearly-allied goldfish, a domestic form (C. auratus) of Chinese origin, has been widely distributed as a pet, and is feral in some places.

The gourami (Osphromenus olfax) of the East Indies has been established in Mauritius and Cayenne, being a valuable foodfish.

The most important case of naturalization of fish is, however, the establishment of some Salmonidae in Tasmania and New Zealand. These are the common trout and sea-trout (Salmo fario and S. trutta); they attain a great size. So far, attempts to establish the true salmon in alien localities have been unsuccessful, but the American rainbow trout (S. irideus) has thriven in New Zealand, and the brook char of the same continent (S. fontinalis) inhabits at least one stream there to the exclusion of the common trout.

Invertebrates

Many insects and other invertebrates, mostly noxious, have been accidentally naturalized, and some have been deliberately introduced, like the honey-bee, now feral in Australasia and North America, and the humble-bee, imported into New Zealand to effect the fertilization of red clover.

The spread of the European house-fly has been deliberately encouraged in New Zealand, as wherever it penetrates the native flesh-fly, a more objectionable pest, disappears.

The wide distribution of three common cockroaches (Periplaneta americana, Blatta orientalis and Ectobia germanica) is well known, but these are chiefly house-insects.

The common small white butterfly of Europe (Pontia or Pieris rapae) is now established in North America; and the march of the jigger, or foot-infesting flea (Sarcopsylla penetrans) of tropical America, across Africa, has taken place in quite recent years.

The Romans are credited with having purposely introduced the edible snail (Helix pomatia) into England, and the common garden snail and slugs (Helix aspersa, Limax agrestis and Anion hortensis) have been unwittingly established in New Zealand. In that country, also, the earthworms of Europe are noticed to replace native forms as the ground is broken.

General Remarks

A great deal has been said about the upsetting of the balance of nature by naturalization, and as to the ill-doing of exotic forms. But certain considerations should be borne in mind in this connexion. In the first place, naturalization experiments fail at least as often as they succeed, and often quite inexplicably. Thus, the linnet and partridge have failed to establish themselves in New Zealand. This may ultimately throw some light on the disappearance of native forms; for these have at times declined without any assignable cause.

Secondly, native forms often disappear with the clearing off of the original forest or other vegetation, in which case their recession is to a certain extent unavoidable, and the fauna which has established itself in the presence of cultivation is needed to replace them.

Thirdly, the ill effect of introduced forms on existing ones may often be due rather to the spread of disease and parasites than to actual attack; thus, in Hawaii the native birds have been found suffering from a disease which attacks poultry. And the recession of the New Zealand earthworms and flies before exotic forms probably falls under this category. As man cannot easily avoid introducing parasites, and must keep domestic animals and till the land, a certain disturbance in aboriginal faunas is absolutely unavoidable. Under certain circumstances, however, the native animals may recover, for in some cases they even profit by man's advent, and at times themselves become pests, like the Kea parrot (Nestor notabilis), which attacks sheep in New Zealand, and the bobolink or rice-bird (Dolichonyx oryzivorus) in North America. Finally, it should never be forgotten that the worst enemies of declining forms have been collectors who have not given these species the chance of recovering themselves. (F. FN.)