Wallace's Line

Abstract

I Introduction n the mid-eighteen hundreds, professor T. H. Huxley wrote of Alfred Russel Wallace, "Once in a lifetime, a Wallace may be found, physically, mentally, and morally qualified to wander unscathed through the tropical wild of America and Asia; to form magnificent collections as he wanders; and withal to think out sagaciously the conclusion suggested by his collections: but, to the ordinary explorer or collector, the dense forest of equatorial Asia and Africa, which constitute the favorite habitation of the orang, the chimpanzee, and the gorilla, present difficulties of no ordinary magnitude: and the man who risks his life by even a short visit to the malarious shores of those regions may well be excused if he shrinks from facing the dangers of the interior; if he contents himself with stimulating the industry of the better seasoned natives, and collecting and collating the more or less mythical reports and traditions with which they are too ready to supply him." Alfred R. Wallace was a self-taught naturalist who spent four years collecting and studying the plant and animal life of the Amazon Basin and another eight years in the Malay Archipelago. On the basis of his observations he formulated his own theory of natural selection and sent an outline to Charles Darwin which then pushed Darwin into publishing his Origin of Species in 1859. Both men had come to the same conclusion as to evolution of the species, hut Charles Darwin will be forever known as the creator of this theory. During the eight years from 1854 to 1862, Alfred Wallace traveled fourteen hundred miles among hundreds of islands in the Malay Archipelago. They included two of the largest, New Guinea and Borneo down to some of the smallest islets. Wallace was a collector, hut more than that he was an astute field observer and he tried to understand the how and why this new environment worked. He had a great opportunity to observe products of nature in their own surroundings that had been little touched by man. He could observe this earth with its own adaptations and adjustments, each plant and animal having its life enriched or destroyed on its own, not by the influence of man. A Fantastic Discovery Wallace spent his first two years in Singapore and around Sarawak, Borneo. It was after this time of apprentice that he decided to move onto other islands. He wanted to first investigate Makassar, Celebes (present day Sulawesi). But travel was very slow and inconvenient in those days and Wallace could not find passage directly from Singapore to Makassar. So he booked passage on a schooner sailing to Buleleng on the north side of Bali. Here Wallace spent several days observing the bird and insect life of Bali. He was delighted with what he saw and he shot and preserved specimens of wagtailed thrush, an oriole, and some starlings. He also collected some beautiful black and orange (on a white background) butterflies that were abundant on a country lane. All of the wildlife he observed on the isle of Bali was similar to the wildlife found on the large island of Java that was directly west of Bali. A few days later he booked passage to Ampenan in the island of Lombok. Leaving Buleleng in Bali, it took only a two-day passage to arrive in Ampenan, Lombok, for it was less than 20 miles between islands. Wallace spent three months on the island of Lombok and naturally expected to see the same plant and animal life he had observed in Bali. The climate and terrain were very similar between these two islands but to Wallace's astonishment he found a totally different set of species, most of which were utterly unknown not only in Java, but in Borneo, Sumatra and Malacca. For instance, white cockatoos were very common in Lombok along with three species of Meliphagidae, or honeycreepers, belonging to family groups that are entirely absent from the western or Inda-Malayan region of the archipelago. As one continues eastward to Flores and Timar, Wallace found that the distinctness from the Javanese species was even more noticeable. The species here were similar to those of New Guinea and Australia. Of interest, in 1845, almost 10 years before Wallace landed in the Malay Archipelago, it was written (by George Windsor Earl) that there was a shallow sea that connected the great islands of Sumatra, Java and Borneo to the Asiatic continent. It was also agreed that there was a similar shallow sea connecting New Guinea and some of the island adjacent to Australia, all being characterized by the presence of marsupials. The Wallace's Line It was this comparison that caused Wallace to recognize the most radical contrast in the Archipelago. He followed it out in detail and drew a line among the islands so as to divide them into halves, the western islands belonging to Asia and the eastern islands being allied to Australia. The terms that Wallace gave these areas were the Inda-Malayan division to the west (Asia) and the Austro-Malayan division to the east (Australia). The term "Wallace's Line" did not come from Wallace himself but was given by T. H. Huxley in honor of Wallace's unexpected discovery. The animals and insects on the western islands resembled those of Asia, while the animals of the eastern islands resembled those of Australia. The middle islands had mixtures of representatives of both continents. The islands east of the Wallace's Line have a distinct flora and fauna with a close resemblance to that found in Australia. Australia is well-known for its unique fauna that differs from all other continents; it possesses no monkeys or apes, no cats or tigers, wolves, bears, hyenas, no deer or antelopes, sheep or oxen, no elephant, horse, squirrel or rabbit - none of those types of animals found throughout the rest of the world. Indeed, Australia is full of marsupials (kangaroos, opossums, wombats, and the Duck-billed Platypus). Its birds are also almost as peculiar. There are no woodpeckers or pheasants to be found, but in their replacement are the mound-building brush-turkeys, honeysuckers, cockatoos, and the brush-tongued lories. These unique birds are not found west of the Wallace's Line. It was surmised by Wallace that the islands west of the division between Bali and Lombok were never joined together with the islands found east of the Wallace's Line. Indeed they formed two distinct continents, one coming from the Pacific and the other being a part of the Asian continent. There was a dividing depth of water between  these two island masses. In ancient times these two continents were as divided as would be the present-day South America and Africa. As time went on with the turmoil of the continental shelves, these two continents were brought together. But instead of the huge land masses, much of the land had been changed, even to the point where much of it was under water, thus forming many islands that were in reality the tops of mountain ranges or volcanoes. This was the explanation for Wallace's great, unexpected discovery. He spent most of his waking hours of the next few years proving this theory.