Alfred Russel Wallace : Alfred Wallace : A. R. Wallace :
Russel Wallace : Alfred Russell Wallace (sic)

 
 
2. Lecture on Animal Life in the Tropics. (1867)

 
Editor Charles H. Smith's Note: A long unpublished work, the second in a series of three lectures Wallace presented at the Literary and Philosophical Society in Newcastle in November 1867. The manuscript from which this transcription is drawn is part of the Alfred Russel Wallace collection at the Natural History Museum (London), item WP9/2/2. The Newcastle Courant issue of 15 November 1867 carries a story on the three lectures, describing this one as having been delivered on 13 November 1867. Item WP9/1/3 in the NHM collection, a list Wallace kept of lectures he delivered, identifies this as one of three "Earliest Lectures," and the 1867 date is in fact by several years the earliest of those listed. Be aware that the 46-page handwritten ms. contains notes to himself as to when to show specimens and such, and that I have simply left them as they appear. It also contains headings in the margins, which I have inserted into the text below in bold italics at approximately the point they appear (sometimes at the beginning of a paragraph, and sometimes not). To link directly to this page, connect with: http://people.wku.edu/charles.smith/wallace/Animal_Life.htm


On the Animal Life of the Tropics

    Our subject for this evening will be, the consideration of the more general phenomena of animal life, as exhibited in the tropical regions, and more especially in the Malay Archipelago.

    Popular Idea of Tropical Animals. The popular view of the characteristics of tropical animals is,--that they are generally of larger size, more numerous and more varied in form, more remarkable in structure, and of more brilliant colours, than those of temperate regions; and there is also, if I mistake not, a very general idea, that these peculiarities are in some way directly due to the heat and light of the tropics,--to the heat as favouring growth,--to the light as developing colour. I propose to enter somewhat into detail on these topics, as regards various classes of animals, and shall endeavour to determine what amount of truth there is in these opinions as facts, and in the explanation given of them, as a theory.

    At the outset of this enquiry, we have to consider that the existence of land animals is altogether dependent upon vegetation, and that we cannot possibly have the one where the other is absent. But the temperate zone as marked out by geographers, includes vast tracts, which for more than half the year are shut up in snow and ice, and where consequently very few animals can maintain themselves. All that depend upon foliage and flying insects for food, all that subsist on fruits gathered from trees or on herbage growing on the ground, must migrate to warmer regions during this season.

    Limits and Extent of Tropics. Almost all central and N. Asia is of this character, as well as N. America, N. of Lat. 50.°; so that the real area of the temperate regions, where a varied animal life during the winter months is possible, will not be much more than half that of the tropics. But we have to consider further, that the tropics of the geographer and of the naturalist, do not coincide. The tropical regions as indicated by the preponderance of tropical forms of animal and vegetable life, almost always extends beyond the tropic of L. 23.° 28'. Almost the whole of the valleys of the Ganges and the Bramaputra, are beyond this line, but their productions are purely tropical as far as 27°. N. Lat. In Brazil tropical forms of insects and birds abound as far as 30° S. Lat.; and in Australia the large tropical butterflies of the genus Ornithoptera extend to Richmond R. in Lat. 29° S.

    Vegetation of Temperate & Tropical Zones as influencing Animal Life. Tropical forms of life occupy therefore a much larger space upon the globe than those which we class as temperate forms, and from this cause alone they should be more numerous. The disproportion of numbers must be further and greatly increased, by the difference in the character of the vegetation of the two regions. The fall of the leaf and the complete absence of flowers during a portion of the year, is the distinguishing feature of temperate as compared with tropical vegetation, and must have an important influence on the comparative abundance of animal life. The absence of flowers and leaves implies an absence of insects, and this will necessitate the death or migration of a number of insectivorous birds quadrupeds & reptiles,--which will again keep down the numbers of the larger carnivorous animals.

    Glacial Epoch. do. But another and more remote cause, has probably influenced the comparative abundance and variety of animal life in the tropical and temperate regions. I allude to the glacial epoch, during which a climate equal in severity to that of Labrador or Greenland, extended over the whole of America N. of the great lakes, and probably over Europe N. of Lat. 50.° thus greatly restricting the area of the habitable temperate zone. It is to be remarked that even if the tropical regions were also lowered in temperature, their animal and vegetable productions would be little affected, since their climate would still be uniform throughout the year; and it is well known that it is the extreme fluctuations, rather than the actual amount of heat and cold, that is predjudicial to most tropical forms of life. This is shown by the occurrence of tree ferns and Parrots in the damp uniform temperate climates of Tasmania & N. Zealand, and by the great height to which many tropical productions ascend on mountains near the equator.

    Causes of variety of Tropical Life. I believe therefore, that the greater abundance and variety of the forms of animal life in tropical as compared with temperate countries, is due,--first, to the greater absolute extent of the tropical regions, and secondly, to the greater uniformity and permanence of their climate, and consequently of their vegetation;--uniformity during the year and during series of years,--and permanence during geological epochs, in which those of more northern and Southern lands have undergone great fluctuations. The direct influence of tropical heat I do not think has had any thing to do with the matter,--chiefly, because the other causes I have mentioned appear to me to be sufficient, and also because, if temperature had much to do with it, its effects ought to be much more uniform. I will adduce a few facts to illustrate this.

    India & Australia. The peninsula of India, or that part of Asia S. of the Ganges and the Indus, is a fertile region entirely within the tropics, with a great variety of hill dale and mountain, and abundance of luxuriant forests. Australia on the other hand is chiefly out of the tropics, is especially deficient in forests, and, allowing for the immense deserts of its interior, has less area available for animal life than India. Yet on comparing the population of Land birds of the two countries, as given by Jerdon and Gould, we find that those of Australia are actually the most numerous.

    The islands of Ceylon and V. Dieman's Land, are about equal in size, but the contrast of their climate is very great, the one enjoying a perpetual summer, and covered with ever verdant forests,--the other exposed to cold blasts from the Antarctic ice-fields and with a cool climate even in summer. Here there is of course a great difference, the one possessing 200, the other only 100 species of land birds; but this seems to me quite sufficiently explained by the excessive difference in the vegetation of the two islands, the abundance of flowers & insects throughout the year in one,--their absence during winter in the other.

    Celebes & Ireland. In the case of Celebes and Ireland, although the differences of climate are about the same as the last the results are different. The rich equatorial island with its perpetual summer, has but 140 species of land Birds; while damp cold northern Ireland has nearly 100.

    Jamaica, Sicily. But a still more remarkable case is that of Jamaica and Sicily, islands of about the same size. Tropical Jamaica has according to Gosse only 100 land birds inhabiting it, while a list has been published of more than 170 found in temperate Sicily.

    The proportionate numbers of this well known class of animals, in tropical & temperate countries of nearly equal extent, varies so irregularly as to give no countenance to the idea that differences of temperature (which are very regular) have any thing to do with it. On the other hand there is reason to believe, that facilities for obtaining food, greatly influence the abundance and variety of species in a group. Water Birds. This is well shown by the case of the water-birds, whose food being obtained chiefly from the sea-shores and marshes, is not dependent on a uniform land-temperature;--and these birds are actually more plentiful more varied and more beautiful, in cold than in hot countries. (See Table.)

    Size of Tropl. & Temperate Animals. We will now endeavour to ascertain what are the real facts, with regard to the alleged greater size and more brilliant colours of tropical animals, when compared with those of temperate regions.

    You will at once call to mind, the Elephant, Rhinoceros, and Giraffe,--the Lion, Tiger and Jaguar, as examples of the large size attained by tropical animals;--but we should also remember the Siberian Mammoth very recently extinct, and the woolly Rhinoceros which inhabited Europe since man existed there, and when the climate was certainly colder than it is now. The tiger at the present day roams over the plains of Siberia and in N. China in a temperate and even a cold climate, and the Jaguar permanently inhabits the United States of America. Then again, the largest of all deer was not one inhabiting the Tropics but the Irish Elk; and the largest of all the Mammalia of America are not found in the tropical regions, since the Bison and the Elk are confined to the temperate and cold districts of N. America. So the largest known sheep, is the Ovis ammon, which inhabits, not the warm plains of India, but the cold mountain plateaux of Thibet and Siberia.

    Birds, Temperate = Tropical in size. Again, birds are by no means generally larger in tropical countries. The owls, eagles and vultures,--crows, grouse, or ducks of the temperate and arctic regions, are fully as large as any in the world; and if the ostrich and the cassowary inhabit the tropics, the Rhea or American Ostrich abounds on the cold inhospitable plains of Patagonia, and the gigantic Moa was very recently an inhabitant of the cool forests of N. Zealand.

    In some other groups another rule prevails. Insects undoubtedly reach a larger size in the tropics,--though this by no means implies a larger average size,--and the same thing may be said of Mollusca. There are some groups of insects, the Carabidœ or ground-beetles for instance, which are actually of larger average size in the temperate regions. The facts, therefore, seem opposed to the statement, that tropical animals are generally much larger than those of cold countries; and when they are so, we can not consider it due to tropical heat; since it would be most illogical to deduce so partial and variable an effect, from a cause which is so universal and unchanging.

    Brilliant Colour. We now come to the chief characteristic, the brilliant colour, which is universally attributed to tropical animals. Is this a general rule, or has it exceptions as numerous and striking as in the cases already discussed? I think I shall best be able to answer these questions, and give a more intelligible explanation of the whole subject, after having given you some account of the chief animal productions of the Malay Archipelago.

    Monkeys. Of all the extensive groups of animals which now inhabit the globe, none is more completely characteristic of the tropical regions, than the Quadrumana or monkeys. With one remarkable exception they are found everywhere in the tropics, and they are especially abundant in the islands of Sumatra & Borneo. These animals are almost wholly dependent on the luxuriant and perennial tropical vegetation, living chiefly on wild fruits as they come successively in season, and wandering about continually in search of fresh supplies. By their peculiar organization they are adapted to an arboreal life, travelling high up among the forest trees as easily as most animals do along the ground, owing to their great activity, their prehensible extremities, and their moderate bulk and weight. Why confined to the Tropics. We can easily understand that such animals are almost necessarily confined to countries where there are no severe winters to cut off the supply of vegetable food. We also see sufficient reason why they should seldom attain a large size; for, as they require to pass continually from tree to tree along the spreading branches, and have frequently to leap (as I have often seen them) 50 feet through the air, great bulk would be inconvenient and predjudicial to them. Apes and monkeys are therefore as a rule, small animals; and the few large ones, the Gorilla, Chimpanzee, and Orang-utan,--are found only in the vicinity of the equator, amid the most varied and luxuriant vegetation, and in a climate so uniform that a constant succession of fruits and succulent shoots is produced throughout the year. Orang-utan. The adult orang-utan is smaller than the Gorilla, yet he weighs as much as a good sized man, and if he had legs in proportion to his body, would be nearly as tall. His habits are truly arboreal. He walks along the larger limbs of the trees, in the attitude shewn in the figure, or sometimes swings himself along by his hands only. In passing from tree to tree he never jumps like the smaller apes or monkeys, but seeks out a place where the boughs of adjacent trees intermingle, and there gathers together with his large hands and long arms, a number of the smaller boughs so as to make a bridge, by which he swings himself across. He is evidently always on the look out for places where he can thus pass, because when I have been in chase of one, he would always get along the trees as quickly as I could along the ground, which would not have been the case if he ever made a mistake, and got on to a branch which did not intermingle with one of an adjacent tree. At night he makes a nest of boughs laid upon a forked branch, and sleeps on it with his head bent in, and his back upwards, so that the long thick hair on that part may carry off the rain or dew. He is an inoffensive animal, but of immense strength, especially in the hands and arms; and the natives say every animal of the forest is afraid to attack him.

    This singular creature is found only in the flat and swampy districts of Borneo, and in a small tract in the N. W. of Sumatra. He has probably been so restricted, by the recent separation of the islands from the continent, and by the accompanying subsidence of the low lands which he formerly inhabited.

    The nearest allies to the orangs are the long-armed apes of the genus Hylobates, which are much smaller and more active and have still longer arms. Their greatest peculiarity is, that they never willingly use their legs in travelling through the forest, but hang by their arms, swinging along hand over hand at a great rate, and often flinging themselves through the air a long distance to another tree or bough, with the greatest ease and certainty. They may often be seen towards the tops of the loftiest trees, hanging by their arms and swinging gently to & fro for a long time, apparently in an attitude of perfect repose. They are often tamed, and are very affectionate and amusing little animals. When on the ground they run alone, quite erect, with a waddling gait, their arms held high up in the air and swinging round and round in a most ludicrous manner. This singular attitude no doubt arises from their desire to reach something above their head, by which to swing themselves along in their favourite mode of progression.

    The rest of the quadrumana of the East, are a variety of monkeys, with shorter or longer tails; and some curious little nocturnal animals allied to the Lemurs,--viz. The Stenops, Tarsius and Galeopithecus, an account of which you will find in any work on Natural History.

    Monkeys not bright coloured. Now it is a curious fact for those who believe that the light of the tropics has any thing to do with the gay colours of its birds and insects,--that this eminently tropical group, the Quadrumana, presents us with a series of dull and sober tints,--blacks, greys, browns and reds of the least attractive character. Perhaps it will be said, they live in the shades of the forest: but so do all the most beautiful birds and insects of the tropics, in fact the majority of all their inhabitants. We see then,--that in this group of animals, in which we should expect to find all the real tropical characteristics very predominant, there is neither large size nor brilliant colour. We have seen reason to believe that size has in them been regulated by the conditions of their existence,--each species having reached that size, which is on the whole best adapted to enable it to maintain and perpetuate the race. In like manner it seems probable, that their sombre colours are due to the fact, that their chief danger from enemies would be during the night, when light or brilliant tints would render them more conspicuous.

    I have said that monkeys are almost universal in tropical countries, with one remarkable exception. In the Australian Region, comprehending besides Australia all the Pacific Is. New Guinea, and the Moluccas, they are entirely wanting. In Sumatra, Borneo, and Java they are very abundant, and one common species has spread along the chain of islands to Timor. In Celebes, the Philippines and in one small island of the Moluccas, a curious black baboon is found, but no true monkey. Beyond these limits no Quadrumana are again met with till we reach S. America.

    Distribution of large carnivora not dependent on climate. Passing on to the next great group of Mammalia, the Carnivora, we have only the tiger at all remarkable for large size or brilliant colouring,--the small tiger-cats, the civets, ichneumons, bears and otters, of the Eastern tropics, being neither larger nor more gayly coloured than the corresponding species of Europe and N. America.

    The fact of the largest cats, as the lion and the tiger, being now chiefly confirmed to hot countries, seems to be dependent on other conditions than those of the climate; since we know that quite recently, species equally large inhabited France and England, when the climate was probably not warmer than it is now. They can live then, wherever abundant food and other suitable conditions concur. What those conditions are, we are often unable to determine; as for example, why the tiger which abounds in Java and Sumatra, should be totally wanting in Borneo, which has a similar climate and almost identical natural productions, and where as far as we can judge every condition would be favourable for its existence.

    The carnivora have nearly the same limits in the Archipelago as the Quadrumana. They are numerous in Java Sumatra and Borneo;--only one or two species inhabit Celebes and the Moluccas, while they are entirely wanting in New Guinea, Australia and the islands of the Pacific.

    Ruminants. In the great order of Ruminants the same general facts are repeated. The deer and wild cattle of these tropical islands are not remarkable for size or colour, as compared with those of Cold countries. They also are totally wanting in New Guinea Australia & the Pacific; while although there are deer in Timor and the Moluccas, they so closely resemble those of Java, that they have probably been introduced at an early period, by man.

    Pachyderms. The large pachyderms, the Elephant, Rhinoceros and Tapir, are found only in the three great western islands. In Sumatra all three are abundant. In Borneo all are scarce, the Elephant and Rhinoceros being confined to the N. E. extremity. In Java the Rhinoceros only is found, and it is of a different species from that of Sumatra & Borneo.

    Squirrels. Even such small animals as the squirrels are similarly restricted. They abound in Sumatra Java & Borneo,--they become very scarce in Celebes and are quite wanting in the luxuriant forests of the Moluccas & New Guinea.

    Pigs. There is only one form of terrestrial animal that seems ubiquitous, and passes across the boundaries that restrict the range of so many others. Wild pigs are found in all the islands, though they differ in every locality, and even Timor and N. Guinea have their peculiar species, which would seem to indicate that they have not been introduced by man. Marsupials. One extensive group remains to be noticed,--the Marsupials or pouched mammalia, whose distribution is exactly the reverse of all the rest. They form the characteristic feature of Australian Zoology, but they also abound in New Guinea, and extend as far west as Celebes and the Moluccas. This however is their limit, not one of the group being found in any island W. of Celebes. In N. Guinea there are Kangaroos, some resembling in form those of Australia, others peculiarly modified for an arboreal life,--real tree-kangaroos. There are also a number of curious opossum-like animals, with thick soft woolly fur, which creep slowly about the trees, feeding on the foliage;--others are no larger than rats and mice which they resemble in form;--and there are some like small flying squirrels; but all are marsupials. As far as is at present known the whole of the mammalia of New Guinea with the exception of pigs and bats are of this type. None of them are however of large size,--none are of bright colours; so that in this pre-eminently luxuriant tropical island, none of the mammalia exhibit the supposed tropical characteristics in the smallest degree.

    Birds. We will now pass to the consideration of the class of Birds, and I have first to call your attention to the fact, that in the most widely distributed groups of birds, those species inhabiting the tropics, are by no means remarkably different in appearance from the denizens of temperate and cold regions. Cosmopolitan groups. The Hawks, Eagles, and Owls, of hot countries, are neither larger nor more brightly coloured than those that dwell near the pole. The larks and thrushes of the tropics, are very much like our own. The goatsuckers have all over the world the same marbled tints;--the swallows have the same glossy plumage, and the crows under the equator are neither more nor less black than those of our own Country. Many other groups are in the same category. The facts are known to every naturalist, and certainly they do not lend any support to the opinion, that the intense light of the tropical sun, directly assists in the development of colour.

    Brilliant Tropical Birds. But if we look at those groups of birds which are almost or entirely confined to the tropics, we shall find,--(it will no doubt be said)--that they are almost all of remarkably bright colours. Parrots, Toucans and Trogons,--Humming-birds, Chatterers, Barbets, Pittas, Tanagers, and Gapers, are all tropical, and have all gay coloured and brilliant plumage. This is no doubt apparently favourable to the theory, that colour is due to tropical light and heat; though the direct connection between the two has not been proved in any one case. Plain Tropical Birds. But a little further enquiry will show us, that this is quite an ex parte statement. There is another side of the question with facts equally striking, to be adduced. The cuckoos, the Ant-thrushes, the American tree-creepers, the Bush shrikes, the Catterpillar catchers, the Timaliidœ, and the Bristle thrushes, and many others are all characteristic tropical groups, comprising a great variety of species all of which are of plain and often of remarkably dull and sombre plumage. In fact, for every group of brightly coloured tropical birds, there is another of equal extent whose limits are plain and sober, so that it is doubtful, whether, in proportion to the whole, more gay coloured birds are found in the tropics than in the temperate regions. I am willing to admit however that the proportion is larger, but I think the fact can be more satisfactorily explained, than by imputing it to the direct influence of the sun's rays. Causes of Colour. Colour is due to a peculiar constitution of the surfaces of bodies, which either absorb certain of the rays of light and reflect the rest,--or, while reflecting all rays, causes them to interfere in such a manner as to destroy certain undulations, and to leave the remainder only to produce the effect of colour. The first, are the colours produced by what we call the colouring matter, in plants, flowers, dyes, &c. The last, or interference colours, are those of soap bubbles, metallic surfaces, mother-of-pearl, and of many of the feathers scales and hairs of animals. Light not necessary. All colour must therefore depend upon minute variations,--either of the mechanical structure of surfaces, or the chemical constitution of animal and vegetable fluids; and there is no proof whatever that light has any thing to with their production, or with the development of one class of colours rather than another. The petals of a flower for instance are fully coloured when they first open, though they have been developed in the dark. The varied hues of the moths' or butterflies' wing, have been produced by organic changes in the chrysalis, often buried deep in the earth or inclosed in a thick cocoon impervious to light. The star fishes which were obtained from the bottom of the Atlantic at a depth of 2 miles, were as brightly coloured as those from the shallow waters of our shores; though not a ray of light can ever penetrate to that profound abyss, and the whole race, perhaps for thousands of generations, has existed in the most absolute darkness. Again, how many earths and minerals display the most gorgeous hues, although for millions of ages they have lain hidden in the bowels of the earth. These facts go to prove, I think, that light is not primarily essential to the production of those peculiarities in natural objects, which determine their colour, except as it increases health and vigour and the changes of structure or composition that affect it, are so minute, that most likely every cause that has any influence on the growth or development of an organism, may also modify its colour. This is indicated by the fact, that the colours of animals and plants are often very unstable. Selection of varieties of Colour. In domesticated animals or cultivated plants, man produces almost what colour he pleases, and this is generally done, not by the supply of colouring matter in food or by exposure to coloured light, but merely by taking advantage of those fluctuations of colour, which are always occurring in nature. He chooses or "selects" the extreme variation in the direction he requires, and throws aside all others. The offspring of this extreme variation will probably, from the law of hereditary descent resemble their parents, varying slightly from it in all directions. Thus some variations will probably occur still further in the direction required, and he again chooses these to breed from, and thus in a comparatively short time he can arrive at the colour he desires. This is artificial selection. The great discovery of Mr. Darwin is, that a process similar to this, which he terms "natural selection", goes on in Nature. For example, take the case of some small desert bird or quadruped, subject to the attacks of hawks and other birds of prey. Supposing that at first it varies in colour like some of our domestic animals, some being white, some black, others red yellow or brown. It is very evident that all those whose colours are most strongly contrasted with the sand on which they live, will be most easily seen from a distance by their enemies the birds of prey, and will be first destroyed; while of those which most resemble the sand they live on a larger proportion will escape. In a few generations therefore, the black and white ones will be exterminated, and a closer selection will commence: those that are too red or too yellow will be most often destroyed, and among the varying descendants of the survivors, some will exactly resemble in colour the soil of the district they inhabit, and so in time these will come to be the only representatives of the original species, of many different colours.

    But a similar change of colour will be often useful to animals seeking prey, as well as to those subject to attack. A jet-black lion would be seen a long way off on the open plains, by the watchers of a herd of antelopes,--but the lion as he is, lying in wait on the desert, exactly resembles in tint a hummock of sand or a lump of rock, and the antelopes would stray towards him unawares. The black lions, if they ever existed, might be starved out, & the whole race reduced to that sandy tint useful to a desert animal. It is a curious confirmation of this view, that the large forest cats have frequently black varieties,--the black jaguar & the black leopard are not uncommon, but a black lion or a black tiger are rarely or ever found. This is because in the gloom of the forest black is less conspicuous than it is on the open desert, or in the grassy Indian jungle and for night-prowling animals is a positive advantage.

    Cats. If we keep steadily in mind the fact, that colours are very varying in nature, and that any variation in a direction useful to the race will necessarily tend to increase in each successive generation we may comprehend much of the apparently irregular distribution of colour in the animal world. For example, almost all the large arboreal cats, the jaguar leopard, cheetah, and the tiger-cats, have spotted skins;--spots which must tend to assimilate with the surrounding foliage, and thus help to conceal the animal. Tiger. The Tiger on the contrary is terrestrial;--he lurks in jungles of high grass and reeds, with which the vertical dark and yellow stripes of his body must blend and assimilate.

    The brighter colours of birds in the tropics, may be imputed in part to their living much among the forest shades, where concealment is easy; whereas the birds of the North, having only leafless trees around them during a large part of the year, colours would be more disadvantageous to them, and have therefore been weeded out by the process I have already described.

    Parrots. The group of birds which is perhaps the most characteristic of the tropics is the Parrot tribe. They are almost as purely tropical as the monkeys and for the same reason;--they are fruit eaters exclusively, and having bulky bodies require a large supply of food. Their generally green colour on the upper surface must be a great protection to them, and make them invisible amid the foliage to their chief enemies, the birds of prey; and their habit of nesting in holes of trees secures their eggs and young against the attacks of monkeys and other animals. Although Parrots are found in all the tropics they are very inequally distributed. (See Table.)

    Distribution. The Malay Archipelago is very remarkable for its Parrots, for in one half of it they are very scarce, while in the other they are exceedingly abundant. In the Malay Peninsula, Sumatra, Java & Borneo, there are only 5 different kinds of parrot known, and you may pass weeks or months without ever seeing one, so that they form no part of the aspects of nature in those islands. In the Eastern half of the Archipelago, on the other hand, there are no less than 86 different species, and one can hardly pass a day without seeing or hearing cockatoos parroquets & lories. They form a part of the scenery and cannot be overlooked. This difference is very striking and remarkable, and exactly corresponds with the difference in the distribution of the larger animals already pointed out. Both besides being so numerous in species & individuals, the parrots of the Austro-Malayan region are also more varied in form structure & colouring, than those of any other part of the globe. Lories. We have here a peculiar group, the Crimson lories,--beautiful parrots in which the prevalent green colour is replaced by vivid crimson, with patches of blue, yellow, or black. They are further remarkable in having extensile tongues furnished with a double series of brush-like papillæ, with which they lap up the nectar and pollen of flowers. About 20 different kinds of these red lories are found in a small district of which New Guinea is the centre, and beyond which not one exists. Besides these, white and black cockatoos and many curious parrots inhabit this district, constituting it the richest part of the globe in this interesting group. Now I think we may see why parrots of such strongly marked colours as red white and black, have been developed only in the Australian region,--in the fact that all the cats civets ichneumons and other arboreal carnivora are entirely absent, and conspicuous colours have therefore not been so disadvantageous as elsewhere. That this is the real cause is rendered almost certain by the remarkable fact, that large black parrots occur also in Madagascar, but nowhere else; and that island is also characterised by the great rarity of carnivorous animals.

    Birds of Paradise. New Guinea is also distinguished as being the region of the Birds of Paradise, perhaps the most marvellous and beautiful of all birds. They inhabit a still more limited district than the crimson lories as they have only been found in three or four islands out of New Guinea itself, and these are all separated from it by shallow water, and have probably not long since formed one connected land. From a very early period, the skins of these beautiful birds have been preserved by the natives, and were obtained by the early navigators, in the Moluccas. They were told strange tales about them, which were for a long time believed in Europe, and seem to have had their origin in the fact that the natives cut off the legs and often the wings leaving only the ornamental plumes.

    [if 40 minutes leave out two pages] Old John van Linschoten, writing in 1598, says; "In these islands only is found the bird which the Portingales call passaros de sol that is "fowl of the sun", and by us called "Paradise Birds, for the beauty of their feathers, which surpass in lustre & beauty all other birds. No one has seen these birds alive, for they are never found except dead: they fly, as it is said, in the air always towards the sun, and keep themselves continually in the air without lighting on the earth, while they are alive, for they have neither feet nor wings, but only head and body, and for the most part tail, as appeareth by the birds that are brought from thence into India, and some from thence hither, but not many, for they are costly." Mr. William Funnell who was at Amboyna with Dampier in 1705, also gives an account of these birds, which is quite as far from the truth as that of the older writers. He says: "The Birds of Paradise are about the bigness of a pidgeon. They are of various colours and are never found or seen alive; neither is it known from whence they come. I have seen several of them here embalmed with spice which preserves them from decay. It is related of these birds that when the nutmegs are ripe, which is in the months of February & March, they resort to the places where they grow, viz. to Banda & this place, and eat of the outer rind of the nut; after which they fall down dead drunk, and an innumerable company of ants gather about them, and feed upon them and kill them."

    These strange accounts show how little was known about these birds, till quite recently, for they are never found in Amboyna Banda or Ternate, and although their native country is so near, it does not seem to have been known to the inhabitants of these places. The reason of this is, that they pass through so many hands before they reach the European purchaser. They are killed and prepared far in the interior of New Guinea. They are brought down to the coast by a native trader perhaps, who knows & cares nothing about them, but as articles of commerce. Here they come into the hands of some chief or local Malay trader. From him they go to the captain or men of some Prau, who bring them to Ternate or Amboyna, and they are sent with other merchandise to the shops, or are hawked about the streets by the sailors. It is no doubt true, that no native who ever came to Ternate or Amboyna had ever seen them alive; & there are to this day several of the known species which no one has seen alive, & the evidence for the existence of which as real birds, is exactly the same as that for the former living existence of fossils.

    I was myself so fortunate as to see many of these birds in their native forests, where they are sometimes abundant. The male birds alone have this beautiful plumage, and they go through several moults, and are probably 3 years old, before they are in perfection. In the breeding season, when they are in their greatest splendour, they hold a kind of social "matinèe", to dance and exhibit themselves. There are certain large trees with scanty foliage, which they choose for the purpose; and here soon after daybreak, perhaps a dozen or twenty fine male birds-of-paradise assemble, and in a state of great excitement fly across from branch to branch, scream and flutter, stretch out their necks, and raise up and shake their magnificent plumes, so as almost to conceal their brown bodies in a gold-coloured feathery fountain. (The natives take advantage of this habit to shoot the birds with bow and arrow from a shelter of boughs carefully prepared in the lower branches of the tree.)1

    I think it is probable that while this display is going on the female birds are watching from the neighbouring trees, and I have no doubt, that the unfortunate bird whose feathers are a few inches too short, or who has not strength and vigour enough to display himself to advantage, will have very little chance of a partner for that season; and thus the beauty of the race is kept up to a proper standard. I wish now to call your particular attention to the fact that these birds of Paradise were probably not always handsome. The females and all birds under a year old, are as plain and dull in colours as any bird of a northern clime, and I firmly believe there was a time when there was no such difference between the sexes as now exists, when all alike were brown or dusky; and that we really owe all the beauty we so much admire in these creatures, to the good taste and judicious conduct of the lady birds-of-paradise. I must explain this a little more fully, as it is one of the most important and ingenious applications of Mr. Darwin's theory. The birds-of-Paradise are allied to the crows and to the Honeysuckers, and among these birds there are often as it were the rudiments of the fine plumage of the birds-of-Paradise. (Exhibit specimens Nect. zenobia, Arachnothera, Poe bird, Manucodia)

    Now if there was a time when the male Paradise-birds had no more ornamental plumage than these allied birds now have, we can easily understand how, by the constant selection of those varieties only which showed increased length & beauty of plumage, the magnificent appendages we now behold might ultimately be reached. But in this case the selection was not made by nature or by man, but by the female birds. They invariably preferred the naturally well-dressed gentlemen,--they utterly scorned and drove out of society such as fell short of the proper and fashionable amount of plumes; and as the offspring generally resemble their parents, some falling short of, and some exceeding them in beauty, and these last continued to be more favoured than the others, it is evident that a continual advance might take place, till it resulted in the superb plumage now developed.2

    Perhaps this will be made a little more clear by its application to ourselves; and it may serve to shew the ladies how much more power they have than they are perhaps aware of. If the women of England, for example, were but unanimous in any one like or dislike,--and inexorably acted upon it,--they could in a few centuries change the appearance or even the character of the English race. Suppose for instance a universal horror seized them, of men above six feet high, or of men with red hair,--and they vowed a solemn vow,--and kept it,--that they would never marry such a man; what would be the result? Why as children generally take after their parents, it is evident that the obnoxious class would decrease in numbers every generation, till in a few centuries long legs and red hair would be absolute rarities.

    Perhaps luckily for us, ladies are never likely to be unanimous in such likes and dislikes, but this is not the case with birds, among which, there is a good deal of evidence that it does occur; and it is the opinion of Mr. Darwin, in which I quite agree with him, that to it we owe among other things the many-eyed train of the peacock, and the elegant plumes of the Birds-of-Paradise.

    I must now say a few words about another group of birds which will illustrate in a striking manner some of the phenomena of tropical life.

    Pigeons. The pigeons may almost be considered a tropical group of Birds, for they diminish rapidly in numbers as they recede from the equator, and vanish altogether before we reach the northern limit of the temperate zone. About 300 different kinds of pigeons are known, and of these not more than 20 are peculiar to the temperate regions. Only 5 are found in Europe and 7 in temperate N. America. In the tropics themselves they are by no means equally distributed.

    India proper has 28 sp. Africa 32. Australia 24. S. America. 50. W. Indies & Mexico 25. Pacific Is. 40. While the Malay Arch. has 118. This region is therefore extraordinarily rich in Pigeons. But not only does it contain more species, but together with the Pacific Is. it furnishes the most curious forms, and the most beautifully plumaged pigeons. Now there must be some cause, for this great inequality in the distribution of birds, which are yet found all over the world; and a close study of those inhabiting the Malay Archipelago, has I think enabled me to point out, what may be the chief cause of this inequality. If we look to the two halves of the Archipelago, which I have before alluded to as exhibiting such remarkable differences in their natural productions, we find, that in the western and larger half there are 43 species of Pigeons, while in the Eastern and smaller division there are 85 species. Now this greatly increased number of Pigeons, coincides with the absence of carnivorous mammalia, & of that otherwise universal tropical order, the Quadrumana. I have had many opportunities of observing, that although monkeys and apes live chiefly on fruits, they are also excessively fond of eggs and young birds; and it is well known that pigeons build open and exposed nests and their young remain a long time helpless. It is very easy to conclude from these two facts, that pigeons can not be very plentiful where monkeys abound. The facts of the case strikingly accord with this. Pigeons are most abundant where there are no quadrumana, and diminish almost in exact proportion to the abundance of those animals. In South America monkeys are preeminently abundant, and pigeons are but moderately plentiful; but in reality they are not found together, almost all the pigeons of S. America being terrestrial species inhabiting the Mountains of Peru & Bolivia & the campos of Paraguay, where there are no monkeys;--while in the forest plains, where monkeys swarm, pigeons are exceedingly scarce. Again we see that in the West Indies & Mexico where there are few or no monkeys, there are half as many pigeons as in the whole continent of S. America. We may thus I think understand why it is, that the true forest pigeons, which live entirely on fruits and never descend on the ground, are so very abundant on these islands; since it is here alone that their greatest enemies are altogether wanting. On the same principles we may also perhaps explain why the upper surfaces of these forest birds should be so generally green. Almost their only enemies must be birds of prey, and as these attack them from above, the more they resemble the foliage among which they live the more secure they must be from attack,--and thus natural selection, as already explained, must tend to eliminate every other colour.

    Green fruit-eating Birds. It is interesting to remark, that a large proportion of the fruit eating birds of the tropics which have not much activity & powers of flight, are generally of a green colour; since besides the Fruit-pigeons and the Parrots, we have the eastern Barbets and the leaf thrushes. On the other hand the insectivorous birds, which are necessarily powerful on the wing, are of more bright and varied colours,--such as the woodpeckers, trogons, pittas, rollers and king-fishers. They do not need concealment, as they seize their insect or other prey by their rapid motions; and bright patches of colour may be no disadvantage to them. Now owing to the comparative scarcity of insects during half the year in cold countries, insectivorous birds must be less plentiful, and thus lead to a deficiency of gay colours, from this cause also.

    Insects. I must not neglect to say something about the insects of these regions, because they have, or are supposed to have, in a pre-eminent degree, the tropical characteristics of large size and brilliant colour. My own impressions, derived from an extensive observation of tropical insects in their native countries, is, that their average size is little if at all greater than in temperate regions; that to make up for a number of very large ones there is a corresponding increase in the very small ones. Colour and Size of Tropical Insects. Insects, being almost all dependent more or less directly on vegetation, we can easily understand, that, in countries where vegetation is preeminently luxuriant and is perpetually renewed, they would probably be very abundant. The large size that many of them reach, may also be due to the fact, that their supply of food is always in excess of their demands; and they are thus able to reach the size that may be on the whole most beneficial to the race, unchecked by those annual or periodical scarcities which in less favoured climes would continually threaten their extinction. It is rather singular, that many of these large insects, especially the butterflies, are adorned with the most brilliant colours, and, in proportion as their wings are large, their flight is generally less rapid, and is sometimes even very slow. We should therefore naturally suppose, that the numerous enemies to whose attacks insects are exposed, Birds, lizards and large voracious insects, would soon exterminate these large and conspicuous insects. That they are not exterminated however, every collection proves; and it is very curious and instructive to trace out the various modes, by which they are protected.

    Protective Resemblances of Insects. One of the most frequent cases, is that in which the form, colour, and habits of the insect, all tend to its concealment. There is a large family of exclusively tropical insects, called Phasmidœ, or Spectre Insects. They are very large, sluggish, leaf-eating insects; soft and succulent, and very tempting to many birds; they have no armor or defensive weapons, they have little or no power of flight, they are too large to find ready places concealment,--yet they are perfectly protected by the marvellous resemblance most of them bear to vegetables. Some have broad leafy wings veined and coloured so exactly like living leaves, that they may be close under one's eyes without the difference being perceived;--others are exactly of the brown tint of dead or dying leaves. These dispose all their limbs and appendages in such a manner that they add to the deception by forming stalks or leaflets.

    Phasmidæ. There is another large group which have no wings, but long stick-like bodies often 8 inches long, or even a foot. In these the head, legs, eyes, antennæ, and every joint in the body, are so formed and coloured as to imitate the bark, knots, buds, and branches of a dead twig.--More than this, as twigs are not generally symmetrical, the insect thrusts out one leg on one side and perhaps two on the other, and hangs loosely among the foliage of a shrub, so as exactly to resemble a piece of dead branch fallen from the trees overhead. I once obtained a species which so closely resembled a twig grown over with moss, that I could hardly believe that the delicate green foliations with which it was covered, were parts of a living animal.

    A large number of beetles lie still during the day, grasping twigs or resting on bark, and these almost always closely resemble in their brown or mottled colouring, the material on which they repose.

    Another large group of insects, the Hemiptera, derive a considerable protection, I have no doubt, from the strong and pungent odour they give out when touched, and this may account for their presenting less striking imitative forms than other groups.

    Mimicking Butterflies. There is an extensive group of butterflies which also give out a strong and peculiar odour, and appear to derive a protection from it; since although they are very weak in structure, and fly slowly, and are rather large and conspicuous insects, they are yet very abundant. But perhaps the most extraordinary fact connected with them is,--that in every part of the world where this strong-smelling group occurs,--other butterflies, no way related to them, yet imitate them exactly in form and colouring, sometimes even to the minutest tints and markings, and to the very habit and mode of flight. This mimicry, as it has been termed, serves exactly the same purpose as the resemblance other insects bear to leaves and sticks, for if the peculiar smell & taste of some insects causes them to escape destruction by insectivorous animals, those which have no such defence may yet get the benefit of it by closely resembling those that possess it. An additional proof that it does have this effect, is given by the fact, that in many cases it is the female only that has this imitative colouring; the reason being that while slowly depositing her eggs, she is more liable to attack; and if she is destroyed before this is done, the entire race is in danger of extinction. It is found that this will account for many of the cases in which the female differs so much from the male as to appear quite a different insect. Of course there has been nothing voluntary in this imitation or mimicry. It has been brought about by the slow action of "natural selection" or the survival of the fittest. Among the slight varieties occurring in every brood, those which at all resembled any of these odour-protected insects, escaped, and left offspring; the rest were exterminated;--and so in the course of many generations these wonderful imitations have been produced, which might lead us to think that nature delighted in masquerade, if we could not trace their origin & purpose.

    Large and Showy Butterflies,--how protected. There are however a number of large and brilliant butterflies, which are not rapid fliers, and which seem to have no special protection, and yet are tolerably abundant; and I know it is a difficulty with many persons, that some insects should require such special means of protection while others seem to do very well without it. I do not feel this difficulty myself, and cannot see why we should refuse an interpretation of one part of nature, because we can not solve all the problems she presents.3 The life of insects is so obscure, and the conditions that determine their abundance or scarcity are probably so varied, that we must be content in most cases with a general notion of the circumstances that may influence it. In the large and showy, but rather weak Papilionidæ, the males seem to be more abundant and are always more brightly coloured than the females; and being thus more exposed to persecution would in some degree save their partners from attack. The very large expanse & shewy colours of their wings, are really often a safeguard, since they are frequently pierced and broken away by birds, while the insect escapes, whereas a smaller insect would have been seized by the body, and destroyed. But their chief safeguard consists in a special protection to the larvæ, which no other butterflies possess; and if this leads to a greater number of the perfect insects being produced, it may well balance a rather larger per-centage of destruction than in some other groups. (Fig. & Describe Larva of Papilio)

    Leaf Butterfly. Another remarkable instance of the adaptation of habit and colouring to the protection of an insect, is that of the Indian butterfly Kallima inachus. This species flies very rapidly, and as it is thus safe on the wing, the upper surface is marked with bright orange & blue. Its' habit is to rest in thickets among dead leaves, with the wings closed, and in that position they resemble so closely the form, veining, and the varying tints & blotches of dry and decaying leaves, that it is impossible to examine a number of them without seeing the protective adaptation. I have often followed one, and seen it alight, and even then had great difficulty in detecting it; for the little tailed projection to the wing comes against the twig the insect is sitting on, so as exactly to form the stalk of a leaf which though dead is still attached. (See Specimens.)

    Besides the large and remarkable insects to which I have called your attention, there are immense numbers which are small and inconspicuous;--besides those adorned with brilliant colours, there are thousands which are dull and obscure; and we cannot therefore consider large size and bright colours, to be universal or even general characteristics of tropical insects. Causes of size and Colour of Tropical Insects. Among the immense number and variety of insect forms, which the never failing vegetation of the tropics nourishes and has nourished for countless ages past,--all possible sizes,--all possible hues,--all possible modifications of form, may have come into existence;--larger size than in temperate climates has been rendered possible by the more regular and abundant supply of food,--more brilliant colours have been compatible with less destruction by the climate, more concealment, & more generally favorable conditions of existence;--but we have no reason to impute one or the other to the direct influence of the tropical light or heat.

    Conclusion. This brief and hasty review of some of the conditions and specialities of animal life in the tropics, leads us to this result. It is true, that animals are more abundant, and of more varied forms in the tropics. It is true, that many peculiar groups are found there which rarely or never extend into temperate regions. It is true, that the most wonderful forms, and the most gorgeous colours, are presented among the animals of tropical countries. But it does not seem to be true, that these peculiarities are at all directly dependent on the tropical climate,--or that they might not, under other conditions, be manifested in an equal or even a greater degree, with a mean temperature and an amount of light not greater than we ourselves enjoy.

    Through whatever climatal variations our earth may have passed, the great equatorial belt must always have been that where the temperature was most uniform. During changes of climate, which, like that of the glacial epoch, must have destroyed much of the vegetable and animal life, in large portions of the temperate zone,--the region of the equator would always have remained thronged with life, and unintermittingly subject to the action of those organic laws, which have been for ever modifying terrestrial forms of life, so as to keep them in harmony with each other, and with external nature.4 That struggle against severities of climate, which must, at all times, have restricted the range of animal variation in the temperate zones, and have checked all such developments of form and colour as coexisted with an incapacity to resist great and sudden changes of temperature,--was not felt in these favoured regions, where a nearly uniform temperature reigned. The struggle for existence was there always much less severe,--food was there always more abundant; and among the varied conditions of existence which were at all times presented there, every variety of form size and colour had in turn its fair opportunity for development.

    We should look upon the tropical regions, therefore, in the light of a more ancient world than the temperate zones;--as a world in which the great laws which have governed the progressive development of life have operated unchecked for countless ages, and have resulted in those infinitely varied and beautiful forms, those wonderful excentricities of structure, and that rich variety of colour, which delight and astonish us in the birds and insects of tropical countries.


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Copyright: Alfred Russel Wallace Literary Estate.
This work is licensed under Creative Commons Attribution - Non-Commercial - Share-Alike 2.0
England and Wales.


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Editor's Notes

    1. Note Figure 34 in The Malay Archipelago, which illustrates this.

    2. Across from this last sentence in the paragraph, in the margin, Wallace wrote in pencil: " ? increased vigour ". There is no indication of how much later he added this remark, but its presence suggests that before November 1867, at least, he was more willing to accept Darwin's stance on sexual selection. Later, Wallace would advance the "increased vigor" model as getting around the issue of aesthetics-based choice: simply, males that were more brightly colored and/or showy were also likely to be more robust in overall health.

    3. This "one theory should not be expected to explain everything" notion is a frequent theme in Wallace's writings: note related comments in, for example, S89, S165, S173, S382, and S649.

    4. The keeping "in harmony with each other" idea was also a long-standing theme in Wallace's evolutionary writings, beginning with the Ternate essay in 1858.

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