Alfred Russel Wallace

“ The richness and varied development of the old fauna of South America, as still existing, proves, however, that the country has always maintained an extensive area; and there is reason to believe that the last great change has been a long continued and steady increase of its surface, resulting in the formation of the vast alluvial plains of the Amazon, Orinoko, and La Plata, and thus greatly favouring the production of that wealth of specific forms, which distinguishes South America above all other parts of our globe. ”

“ The preponderating influence of the organic over the physical environment, as taught by Mr. Darwin, leads us to give most weight to the first of the above-mentioned causes; to which we may also impute such undoubted cases of survival of ancient types as the Centetidæ of the Antilles and Madagascar—both areas strikingly deficient in the higher vertebrate forms. The probable mode and time of the cross migration between Australia and South America, has been sufficiently discussed in our chapter on the Australian region, when treating of the origin and affinities of the New Zealand fauna. ”

“ Hardly less remarkable is the absence of many wide-spread groups. With the exception of one genus in the West Indian islands and a Sorex which reaches Guatemala and Costa Rica, the Insectivora are wholly wanting; as is also the extensive and wide-spread family of the Viverridæ. It has no oxen or sheep, and indeed no form of ruminant except deer and llamas; neither do its vast forests and grassy plains support a single form of non-ruminant ungulate, except the tapir and the peccary.
Birds.—In birds, the Neotropical region is even richer and more isolated. ”

“ It seems most probable that the great development of land-shells in islands, is due to the absence or deficiency of the vertebrata, which on continents supply a variety of species adapted to prey upon these molluscs. This view is supported by the fact, that in such islands as have been united to a continent at no very distant epoch, and still maintain a continental variety of vertebrata, no such special development of land-shells has taken place. If we compare the Philippine islands with the Sunda group, we find the development of vertebrata and land-molluscs in inverse ratio to each other. ”

“ The land-birds are much more interesting. All except the birds of prey belong to American genera which abound on the opposite coast or on that of Chili a little further south, or to peculiar genera allied to South American forms. The only species not peculiar are, Dolichonyx oryzivorus, a bird of very wide range in America and of migratory habits, which often visits the Bermudas 600 miles from North America,—and Asio accipitrinus, an owl which is found almost all over the world. ”

“ The West Indian Islands being a rich shell district, produce a number of peculiar forms, and the west coast of South America is, to some extent, peopled by Oriental and Pacific genera of shells. On the west coast there is hardly any coral, while on the east it is abundant, showing a difference of physical conditions that must have greatly influenced the development of mollusca. When these various counteracting influences are taken into consideration, the identity or close affinity of about 140 species and 40 genera on the two sides of the Isthmus of Panama becomes very important ”

“ Cuba has rather more species than Jamaica; but while the former has only 1 peculiar genus (Diplopoma) , the latter has 3 (Geomelania, Chittya, and Jamaicea) , as well as two others only represented in the other islands by single species. From Hayti, only about one-third as many species are known as from the two former islands. It has no peculiar genera, but it has some forms in common with Cuba and others with Jamaica, which show that those islands have more connection with it, than with each other; just as we found to be the case in birds. ”

“ Land Shells.—The Neotropical region is probably the richest on the globe in Terrestrial Mollusca, but this is owing, not to any extreme productiveness of the equatorial parts of the continent, where almost all other forms of life are so largely developed, but to the altogether exceptional riches of the West India Islands. The most recent estimates show that the Antilles contain more species of land shells than all the rest of the region, and almost exactly as many as all continental America, north and south. ”

“ We must exclude, however, the islands of Trinidad, Tobago, and a few other small islands near the coast, which zoologically form a part of the main land. Again, the South Temperate portion of the continent, together with the high plateaus of the Andes to near the equator, form a well-marked subdivision, characterised by a peculiar fauna, very distinct both positively and negatively from that of the tropical lowland districts. The rest of Tropical South America is so homogeneous in its forms of life that it cannot be conveniently subdivided for the purposes of a work like the present. ”

“ No naturalist can study in detail this single family of birds, without being profoundly impressed with the vast antiquity of the South American continent, its long isolation from the rest of the land surface of the globe, and the persistence through countless ages of all the conditions requisite for the development and increase of varied forms of animal life. ”

“ The great mass of Neotropical butterflies are forest species, and have been developed for countless ages in a forest-clad tropical country. The north temperate butterflies, on the other hand, are very largely open-country species, frequenting pastures, mountains, and open plains, and often wandering over an extensive area. These would find, on the higher slopes of mountains, a vegetation and conditions suited to them, and would occupy such stations in less time than would be required to adapt and modify the forest-haunting groups of the American lowlands. ”

“ The snakes (Ophidia) differ from all other reptiles, and from most other orders of vertebrates, in the wide average distribution of the families; so that such an isolated region as the Neotropical possesses no peculiar family, nor even one confined to the American continent. The families of most restricted range are—the Scytalidæ, only found elsewhere in the Philippine islands; the Amblycephalidæ, common to the Oriental and Neotropical regions; and the Tortricidæ, most abundant in the Oriental region, but found also in the Austro-Malay islands and Tropical South America. ”

“ In the only other group of Lepidoptera we can here notice, the Sphingina, the Neotropical region possesses some peculiar forms. The magnificent diurnal butterfly-like moths, Urania, are the most remarkable; and they are rendered more interesting by the occurrence of a species closely resembling them in Madagascar. Another family of day-flying moths, the Castniidæ, is almost equally divided between the Neotropical and Australian regions, although the genera are more numerous in the latter. The American Castnias are large, thick-bodied insects, with a coarse scaly surface and rich dull colours ”

“ Insects.—The various West Indian islands have not been well explored entomologically; one reason no doubt being, that their comparative poverty renders them little attractive to the professional collector, while the abounding riches of Central and South America lie so near at hand. We can, therefore, hardly tell whether the comparative poverty, or even total absence of some families while others seem fairly represented, is a real phenomenon of distribution, or only dependent on imperfect knowledge. ”

“ A peculiar mouse, a species of the American genus Hesperomys, is said to inhabit Hayti and Martinique, and probably other islands. A Dasyprocta or agouti, closely allied to, if not identical with, a South American species, inhabits St. Vincent, St. Lucia, and Grenada, and perhaps St. Thomas, and is the only mammal of any size indigenous to the Lesser Antilles. All the islands in which sugar is cultivated are, however, overrun with European rats and mice, and it is not improbable that these may have starved out and exterminated some of the smaller native rodents. ”

“ Of important genera which range beyond the region, Dicerca is mainly Nearctic and Palæarctic; Cinyra has a species in North America and one in Australia; Curis is divided between Chili and Australia; the Australian genus Stigmodera has a species in Chili; Polycesta has a species in Madagascar, two in the Mediterranean region, and a few in North America; Acherusia is divided between Australia and Brazil; Ptosima has one species in south temperate America, the rest widely scattered from North America to the Philippines; Actenodes has a single species in North America and another in West Africa ”

“ Owing to the lofty mountain range situated along its western margin, the moisture-laden trade winds from the Atlantic have free access to the interior. A sufficient proportion of this moisture reaches the higher slopes of the Andes, where its condensation gives rise to innumerable streams, which cut deep ravines and carry down such an amount of sediment, that they have formed the vast plains of the Amazon, of Paraguay, and of the Orinooko out of what were once, no doubt, arms of the sea, separating the large islands of Guiana, Brazil, and the Andes. ”

“ We learn, then, from the fauna of these islands, some very important facts. We are taught that tropical land-birds, unless blown out of their usual course by storms, rarely or never venture out to sea, or if they do so, can seldom pass safely over a distance of 500 miles. The immigrants to the Galapagos can hardly have averaged a bird in a thousand years. We learn, that of all reptiles lizards alone have some tolerably effective mode of transmission across the sea ”

“ On the other hand the "Turdoid Passeres," consisting of 23 families and comprising all the true "singing-birds," is poorly represented in America; no family being exclusively Neotropical, and only three being at all fully represented in South America, though they comprise the great mass of the Old World passeres. These peculiarities, which group together whole series of families of American birds, point to early separation and long isolation, no less surely than the more remarkable structural divergences presented by the Neotropical mammalia. ”

“ But, as the mountains rose, another set of organisms would make their way along the highest ridges. The abundance and variety of the North Temperate Carabidæ, and their complete adaptation to a life on barren plains and rock-strewn mountains, would enable them rapidly to extend into any newly-raised land suitable to them; and thus the whole range of the Rocky Mountains and Andes would obtain a population of northern forms, which would overflow into Patagonia, and there, finding no competitors, would develope into a variety of modified groups. ”

“ The great continent of South America, as far as we can judge from the remarkable characteristics of its fauna and the vast depths of the oceans east and west of it, has not during Tertiary, and probably not even during Secondary times, been united with any other continent, except through the intervention of North America. ”

“ To the north of Cuba and Hayti are the Bahamas, an extensive group of coral reefs and islands, 700 miles long, and although very poor in animal life, belonging zoologically to the Antilles. All the larger islands, and most of the smaller ones (except those of coral formation) are very mountainous and rocky, the chains rising to about 8,000 feet in Hayti and Jamaica, and to nearly the same height in Cuba. All, except where they have been cleared by man, are covered with a luxuriant forest vegetation ”

“ The importance of the division here pointed out will be seen, when we state, that indigenous mammalia of peculiar genera are found on the western group of islands only; and it is on these that all the chief peculiarities of Antillian zoology are developed.
Mammalia.—The mammals of the West Indian Islands are exceedingly few, but very interesting. Almost all the orders most characteristic of South America are absent. There are no monkeys, no carnivora, no edentata. Besides bats, which are abundant, only two orders are represented; rodents, by peculiar forms of a South American family ”

“ It is a remarkable fact that so many of the species belong to genera which are wholly Neotropical, and that the specially South American families of Icteridæ, Tyrannidæ, Dendrocolaptidæ, Pteroptochidæ, Trochilidæ, and Conuridæ, should supply more than one-third of the species; while the purely South American genus Phrygilus, should be represented by four species, three of which abound in Tierra del Fuego. ”

“ It thus appears, that in the Reptiles all the groups are typically American, and that most of the peculiar genera belong to families which are exclusively American. The Amphibia, on the other hand, present some interesting external relations, but these are as much with Australia as with the North temperate regions. The Bombinatoridæ are indeed Palæarctic, but a larger proportion are Neotropical, and one genus inhabits New Zealand. The Chilian genus Calyptocephalus is allied to Australian tropical genera. ”

“ These groups of islands are both situated in stormy seas, and the immigrants are so numerous that hardly any specific change in the resident birds has taken place. The Galapagos receive no such annual visitants; hence, when by some rare accident a few individuals of a species did arrive, they remained isolated, probably for thousands of generations, and became gradually modified through natural selection under completely new conditions of existence. Less rare and violent storms would suffice to carry some of these to other islands, and thus the archipelago would in time become stocked. ”

“ Land-shells, being so few and small, and almost all modifications of one type, are a clear indication of how rare are the conditions which lead to their dispersal over a wide extent of ocean; since two or three individuals, arriving on two or three occasions only during the whole period of the existence of the islands, would suffice to account for the present fauna. Insects have arrived much more frequently ”