rhinoceros, Sumatran tigers and Borneo leopards, all kinds of monkeys, the orangutans
of Sumatra and Borneo, and numerous birds that are specific to Asia. On the Australasian
side are the marsupials such as the possum-like cuscus and the tree kangaroos, as well
as birds specific to Australasia such as white cockatoos, honeyeaters, brush turkeys
and the spectacular birds of paradise. By his observations, Alfred Russel Wallace had
made a major contribution to a new science, that of biogeography, or of the relationship
between zoology and geography.
The great arc of the Indonesian archipelago starts north of the island of Sumatra
and curves south, east and north until it reaches Papua New Guinea. This arc of islands
is defined by a string of active volcanoes in Sumatra, Java, Bali, Lombok, Sumbawa
and Flores that erupt as the Australian oceanic plate is subducted under the island
arc. Further east the island arc has been pushed to the north and then to the west
by the Australian continent which has been relentlessly marching northward since
it separated from Antarctica 50 million years ago. Papua New Guinea is part of the
Australian continent and this journey north slowed about 20 million years ago when
Papua New Guinea collided with the Pacific Plate. The huge Pacific Plate is moving
westward and the resulting collision rafted segments of Papua New Guinea hundreds
of kilometres towards the west and pushed the Indonesian island arc back upon itself.
The tectonic stress caused by the continuing collision of Papua New Guinea with the
Pacific Plate has thrust the mountains of Papua New Guinea up to a height of 5000
metres above sea level, where a tropical glacier still exists only four degrees south of
the equator.
Eastern Indonesia represents a unique part of the earth’s surface, because it is here
that four of the earth’s great tectonic plates – the Eurasian Plate, the Indo-Australian
Plate, the Philippine Plate and the Pacific Plate are in collision with each other. In the
region of Maluku (the Moluccas), these powerful forces fused together volcanic island
arcs, continental fragments sheared off from Papua New Guinea, seafloor sediments
and coral reefs to create new land, forming the unusually shaped islands of Sulawesi
and Halmahera. A subduction zone then formed along the western side of Halmahera,
causing volcanoes to erupt out of the sea and spreading a thick layer of volcanic ash
across the adjacent islands.
Nature abhors a vacuum, and the rich volcanic soils of these newly emergent
islands were quickly populated by coconut trees grown from coconuts washed up on
their shores, by plants whose seeds blew with the winds, by birds and butterflies able
to fly from island to island, and by animals and insects drifting on floating trees and
branches. Tropical temperatures and monsoonal rains provided the environment for a
diversity of plant, bird and other animal species to thrive and evolve in unique ways.
The profusion of islands allowed for a separation in the evolution of different species
and became an ideal natural laboratory for scientific study. Alfred Russel Wallace
Prologue 9