The populations in question are largely east of Huxley’s Line, a natural boundary that separates New Guinea, Australia, and the Philippines from the western parts of Indonesia and the Asian mainland. This line was described by the nineteenth-century British naturalist Alfred Russel Wallace, and adapted by his contemporary the biologist Thomas Henry Huxley to highlight differences in the animals living on either side, for example, it roughly forms the boundary between placental mammals to the west and marsupials to the east. It corresponds to deep ocean trenches that have formed geographical
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