Montag, 13. April 2009

The lost continent ... or Wallacea

In 1858 the small island of Gilolo (today known as Halmahera) in the Moluccas archipelago was one of the remotest regions left on the globe.
A letter send on the 9. March 1858 from the nearest post station – on the island of Ternate- had first to be shipped to Singapore. From there a post ship of the British P & O Steamship Company, connecting Hong Kong to Suez, brought it on the African continent. By being transported until Alexandria, the letter where again shipped over the Mediterranean sea to Paris and Rotterdam, and finally London. So after three months finally the letter arrived timely in the morning to Down House, Bromley, Kent – 26 kilometres southeast of London, and 12.000 kilometres east of New Guinea.

This letter contained a 20 page long article with the title “On the Tendency of Varieties to Depart Indefinitely from the Original Type” - containing first concepts to maybe explain the rich biodiversity, the geographical distribution and the development of new species from ol
der ones in Indonesia – to enlarge upon a similar thema of the 35 years old author published in a paper in 1855.
The author of the letter to C. Darwin was Alfred Russel Wallace, an autodidact in natural science born in a poor family on 8. January 1823 in the welsh city of Usk.

A photograph of A.R. Wallace taken in Singapore in 1862 (from Wikipedia)

Working first as a surveyor and then as a teacher, he developed a passion for botany and natural science, finally so strong, that in 1848 he started on an expedition to South America. Only in 1852, after four years of collecting an incredible variety of animal and plant species, he decided to return back to England.
But then the catastrophe – the ship on which he was travelling, the trader “Helen”, cached fire and sunk in the North Atlantic Ocean. Wallace could save only some dra
wings – when he finally arrived to England, 1. October 1852, he virtually had lost everything – his collection, his payment (he made a living by selling collected specimens to museums and collectors) and his hope to get reputation by the prestigious british scientific establishment. Only the insurance sum for his transported collection saved him from financial ruin. But lacking all his collected specimens and data he was able to publish only an “abstract” of his discoveries, denominated “A narrative of Travels on the Amazon and Rio Negro”, a book, poorly considered at this time.
Swearing to never again travel by ship, just one year later the old passion grow so strong, that he embarked on a ship to Indonesia, one of the poorest known regions by the European scientist and naturalists.

The 20. April 1854 he arrived to Singapore. He will remain for 8 years, travelling for more than 22.000 kilometres, collecting and sending back to England more then 125.660 specimens of animals, and discovering 1.500 new species of insects and birds.
This second expedition will be published in 1969 in the book “The Malay Archipelago”, and will establish Wallace as founder of the scientific discipline of biogeography.

The voyage of Wallace between 1854 an 1862 (References).

Ironically it was he’s bad luck that give him the opportunity of an important discovery. 31. January 1856 he missed the ship that should bring him to Sulawesi. For 4 months he was “trapped” in Singapore, until he decided to take a detour by passing on the islands of Bali and Lombok.
On these two islands he noted something important; eve
n if the two islands are separated only by a 30 kilometres broad sea passage, the species of animals found differ considerably, dominated by one side by tigers, rhinoceros, primates and on the other side by kangaroos, koalas and birds of paradise. He will describe these two regions in his paper “On the Zoological Geography of the Malay Archipelago” (1859), separating the west ndio-malayan from the east austro-malayan region.“This islands differ far more from each then another in their birds and quadrupeds then do England and Japan, broths of which features animals common on the Eurasian landmass.”
Even if Wallace couldn’t know about the regional tectonics of Indonesia, nor the changes in sea level, he argued that “Such facts can be only explained by great changes of the earth surface."
The explanation first supposed by Wallace will find confirmation only later.
During the ice age vast amounts of water where trapped in the polar ice caps, the sea level during the maximal expansion of the ice was 180m lower then today, creating a landmass where today is sea, called in the east "Sunda-land" (after the continental shelf) connecting Borneo, Sumatra, Java and Bali with Asia, and in the west "Sahul-land", connecting New Guinea with Australia. The islands of Celebes, Timor and Flores, remaining isolated even with sea level low, are referred as "Wallacea". Only islands or regions surrounded by deeper sea represent barriers that animals coming from the Asian or Australian continents couldn’t reach. This barrier will be become known as Wallace Line.

Bathymetry of Indonesia, showing areas in red within a depth of 200m under sea level.

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