In 1854 Wallace started his second great voyage, this time into the Malay Archipelago. With Singapore as kind of a base he undertook some seventy extensive journeys over the huge archipelago which stretches out 1,300 miles in north-south and 4,000 miles in east-west direction. Here he collected over 125,000 specimen of animals, most of them insects, but also numerous amphibians, birds and mammals. Many of them were new to science. One of the famous specimen is the 'Wallace flying frog' or 'gliding tree frog' (Rhacophorus nigropalmatus). Wallace depicted in detail how this species was in a state of transfer.
The 'Wallace Frog', a so called 'flying frog', rather a sliding frog, jumping from a higher point, e.g. a tree, to another plant several meters away, what saves him the effort and danger to climb down, walk over and climb up again on the other side. A species in transfer, using it's webs for gliding. Sketches by A.R. Wallace, the two left in his notebook, the one right is an illustration in 'The Malay Archipelago' (1969)
Wallace was one of the, if not the first Westerner who observed and caught some of the legendary paradise birds in their natural habitats. He sent a collection of them to England.
Hunting Orangutans
Wallace is well known for collecting countless of insects and discovering a great number of till then unknown species. In fact he collected anything he could get in the jungle and sent it to England. The complete title of his book from the East Indies is: "The Malay Archipelago:
The land of the orang-utan, and the bird of paradise. A narrative of travel, with studies of man and nature." The most spectacular animals he collected were mammals and birds of paradise. Since Wallace was depending on making an income from his collections, he hunted all animals. It's pitifull to read over many pages how he is chasing orangutans in the jungle and shooting them in the treetops. For a hunting experience he had, when he shot a mother orangutan and tried to grow up her baby, have a look at the orangutan page.
A Dayak getting bitten by an orangutan while chasing him. Sketch from 'The Malay Archipelago' (1869)
On Borneo Wallace lived among the Dayak (Dyak) people in the jungle. The Dayak had a notorious recommendation as head-hunters. They also hunted orangutans when they came close to their villages. Wallace notes that they did so because the great apes were eating from the same sources of fruits around as the villagers did. Let's have a look for an incident of that kind in his own words (the term 'Mias' used by Wallace is the Dayak word for orangutan):
"(...), on June 4th, some Dyaks came to tell us that the day before a Mias had nearly killed one of their companions. A few miles down the river there is a Dyak house, and the inhabitants saw a large Orang feeding on the young shoots of a palm by the river-side. On being alarmed he retreated towards the jungle which was close by, and a number of the men, armed with spears and choppers, ran out to intercept him. The man who was in front tried to run his spear through the animal's body, but the Mias seized it in his
hands, and in an instant got hold of the man's arm, which he seized in his mouth, making his teeth meet in the flesh above the elbow, which he tore and lacerated in a dreadful manner. Had not the others been close behind, the man would have been more seriously injured, if not killed, as he was quite powerless; but they soon destroyed the creature with their spears and choppers. The man remained ill for a long time, and never fully recovered the use of his arm.
They told me the dead Mias was still lying where it had been killed, so I offered them a reward to bring it up to our landing-place immediately, which they promised to do. They did not come, however, till the next day, and then decomposition had commenced, and great patches of the hair came off, so that it was useless to skin it. This I
regretted much, as it was a very fine full-grown male. I cut off the head and took it home to clean, while I got my men to make a close fence about five feet high round the rest of the body, which would soon be devoured by maggots, small lizards, and ants, leaving me the skeleton. There was a great gash in his face, which had cut deep
into the bone, but the skull was a very fine one, and the teeth remarkably large and perfect."
From A.R. Wallace, 'The Malay Archipelago', 1869, Vol. I
Wallace Line and Wallacea
When crossing the deep-sea trench between Bali and Lombok as well as between Borneo and Sulawesi Wallace noticed a significant change in biology. The Southeast Asian tropical fauna and flora changed to a rather Australian, but it was still different. Some of the islands between the great Sunda islands and Australia and New Guinea have very isolated and peculiar populations, whereas further southeast they are close to the biology of Australia. In the last ice age, Wallace concluded, there was a land bridge between the major Southeast Asian islands as Sumatra, Java, Bali, Borneo and the Malay Peninsula, whereas Australia was connected with Papua New Guinea and others. Some of the islands between the continents were always isolated. Few or no mamals settled down there, and the higher species living there arrived on chance on rafts or were mostly birds or brought by immigrating humans.
A stylized painting of Wallace in the jungle, with his notebook and two birds of paradies in front of him, nicely dressed, in the background his jungle hut.
This biogeographical border across Southeast Asia is now called the 'Wallace Line'. The Wallace Line is the most distinctive biogeographic border on the planet.
In addition to the Wallace Line there are two other biogeographic lines further southeast. The Lydekker Line separates Australia and New Guinea from the islands northwest of them. The differences have their cause in the last ice age. 70,000 to 40,000 years ago the sea level was about 50 to 125 meters lower than it is now; considerable parts of the world's oceanic waters were frozen and piled up at the arctic poles who were much larger than they are now. Therefore the great Sunda islands Sumatra, Java, Bali and Borneo were connected with the Southeast Asian mainland, while Papua New Guinea (Irian Jaya) was connected with Australia. Both land blocks hosted different kinds of species, who were later, when the sea level lowered and the populations were isolated on a number of different islands, evolving in certain, local ways, adapting to the changing environments.
One of Wallace's cottages. In: 'The Malay Archipelago' (1869).
That explains why there are tigers on Sumatra and still were on Java and Bali in Wallace's time, who developed over thousands of years of isolation then slight differences. It's the same thing with the orangutans on Sumatra and Borneo, and there are many, many more examples for the separation of species and their evolution after being cut off from the mainland. There was for instance the immigration of homo erectus to Java (the 'Java Man'), early humans who used the landbridge in an earlier ice age than the last one.
Between the two big former land blocks of Australia (Sahul) and Southeast Asia (Sunda) are a number of islands who didn't belong to one of these blocks but were isolated since much, much longer, as Sulawesi for instance. They are surrounded by a sea deeper than 90m and there developed other certain species, very particular ones. Immigration barely happened, only when small groups of individuals survived being drifted accidentally from the mainlands to the islands. This group of islands is called 'Wallacea', bordered by the Wallace Line and the Lydekker Line.
Map of Wallacea with the Wallace Line, the Lydekker Line and the Weber Line. Wallacea is the region between the Wallace Line and the Lydekker Line. As so often, at a closer look things become more complicated. The Wallace Line has two variations, including or excluding the Philippine Islands. The Philippines weren't travelled by Wallace. In the south there is another biogeographical border introduced in 1899/1900 by the scientist Max W.C. Weber as a result of the Siboga expedition. One has to consider that the borders do not only separate islands but also include maritim life.
Wallacea is a biological 'hotspot', because it is home to a great number and variety of endemic species (they only appear here, nowhere else on earth), both land and water species. Wallacea stretches over 346,000km2. As anywhere else in Southeast Asia these hotspots are under heavy threat. The global socioeconomic system is based on profit and the suicidal fiction of eternal growth, therefore it lives parasitic from the exploitation of nature (and labour). Since the 1850s a great part of the local biodiversity got destroyed already, and the speed of destruction seems to accelerate.
Removal of an intruder. Illustration from 'The Malay Archipelago' (1869)
In Southeast Asia Wallace elaborated his ideas on evolution and the origin of species. Particularly legendary is his splendid idea of the natural selection, which was an inspiration he had when suffering heavy fevers caused by a malaria infection and was still thinking his ideas over and over.
In 1858 Wallace wrote his legendary essay on natural selction in a letter to Charles Darwin. The essay was published in England and triggered finally Darwin's long delayed decision to publish his theory of evolution in his main work 'The Origin of Species' (1859). Darwin feared now very much he could be too late.
In 1868 Alfred Russel Wallace published his studies and adventures in Southeast Asia in his famous scientific travel narrative 'The Malay Archipelago', which became one of the most populous scientific works of the 19th century. Wallace dedicated it to Charles Darwin who praised the book. Also Charles Lyell and the famous novel author Joseph Conrad, who used it as an important source of information for his famous novel 'Lord Jim' and others, very much appreciated the work.