Little Species, Big Mystery: The Story of Homo Floresiensis by Debbie Argue

Author:Debbie Argue [Argue, Debbie]
Language: eng
Format: epub
Tags: Science, Paleontology, Life Sciences, biology, Evolution
ISBN: 9780522877922
Google: D4xyEAAAQBAJ
Publisher: MelbourneUP
Published: 2022-08-02T20:33:20+00:00

W. Earle’s map of 1845 showing the Great Asiatic Bank. Reproduced with the kind permission of the Royal Geographical Society of London.

Wallace was not merely a collector of rare species, or species previously unknown to the scientific establishment. He was also a keen observer, a scientist of nature. He is famous for developing the theory of evolution, or, as he called it, ‘a Law of Natural Descent’,36 at the same time as Charles Darwin—Darwin and Wallace’s ideas were presented concurrently to the Linnean Society of London on 1 July 1858.37 But Wallace was just as absorbed with resolving the question of the odd distribution of species across South-East Asian islands as he was with evolution.

Wallace went on to identify a virtual north–south boundary that separates the faunal types of the Philippines and western Indonesia from the eastern Indonesian islands. He explained his findings in a letter to a friend, Walter Bates, on 4 January1858: ‘The boundary line often passes between islands closer than others in the same group. I believe the western part to be a separated portion of continental Asia, the Eastern, the fragmentary prolongations of a former Pacific continent.’38

Today, we call this species boundary the Wallace Line (see Figure 1 at the beginning of chapter 1). It closely follows the eastern edge of the shelf that Earle identified in 1845. But Wallace was initially unaware of Earle’s work, only hearing about it in 1859 when he received a letter from Charles Darwin in which Darwin mentions Earle’s publication.39 Later, Wallace incorporated Earle’s underwater bank into his theory and proposed that changes in sea levels must have occurred on a grand scale in the past. When sea levels fell, the shelf identified by Earle would be exposed, greatly expanding the Asian landmass,40 and thus enabling the Asian species to freely move around. Those remaining on Sumatra, Java and Bali are therefore those that arrived when the islands were connected by land.41

So now we can see how H. erectus probably got to Java: by wandering overland during a period of low sea levels. But how can we explain the presence of hominins on Flores if we believe they came via the islands of Java, Bali and Lombok? As Wallace deduced, deep channels separate the islands east of Bali from Lombok. Even when sea levels were low in the past, these islands were never joined—they never formed a single landmass. Animal species from Java did not get further east; they did not cross the Wallace Line and they are not on Flores. It is highly unlikely, then, that hominins walked to Flores.

A possible alternative explanation for how hominins got to Flores is that they found themselves making accidental sea crossings. In that case, at least three crossings would be involved: from Bali to Lombok, Lombok to Sumbawa, and Sumbawa to Flores. More crossings, of course, would be required at periods of high sea levels when Bali was separate from Java and Java was separate from Sumatra.

The straits between these islands are relatively narrow and it is no big deal these days to travel between them in motorised boats.

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