On an Imaginary Line

This story isn’t about something with a surprise ending or a big reveal. No, this story is odd enough on its own that it needs no build-up or hype. It takes place even today in the Malay Archipelago, the area of our world where you can find modern nations like Indonesia and New Guinea. It’s both a real but still imaginary line that has baffled scientists and biologists for centuries.

And what makes it significant is that it’s a line that certain animals absolutely do not cross.

Technically, the line, known as the Wallace Line (after the Victorian-era scientist who studied it), separates animals from the Asian continent from those found in the Australian ecosystem. The phenomenon was recognized as early as the 1500s by Spanish members of Magellan’s voyage.

Now, you might think that this isn’t unusual that different animals can be found in different parts of an area, but it really is unique. Some of the islands in that area have tigers and elephants and hippos, but, then, east of the Wallace Line, those animals are replaced by lizards and marsupials in the Australian biosphere.

And the closest those diverse island areas are to each other is less than 20 miles at some points. Even most birds won’t cross the Wallace Line, with the Asian species staying on their side and the Australian species on theirs. Bats are really the only mammal that will cross it, but even those species that do are few and far between. The study of biogeography owes much to the study of exactly why this happens the way it does. Biogeography has divided the earth into 8 different zones rather than continents, but it’s the continents that hold the key to the Wallace Line.

Scientists could easily observe this phenomenon and did so for years, but they had difficulty figuring out exactly why. It wasn’t until geologists proposed the idea of plate tectonics, the movement of large surface plates on the earth, as the source of the Wallace Line. As you probably know, the large land masses (continents) on the earth are moving. That movement as they rub up against each other often causes earthquakes and awakens/creates volcanic activity as the molten innards of the earth bubble upwards as the fissures are created. The different continents created deep crevices in the oceans and seas that led to a separation of species that they still to this day do not cross.

Interestingly, most plants do not recognize the Wallace Line.

But the animals–the animals still won’t.


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