Riddle of the Human Hobbits : An Equinox Special

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Dr Martin Brookes

April 2005

Small But Perfectly Formed

Flo's discovery has turned up many unanswered questions, but the overwhelming enigma is her size. Doubts still linger in certain corners of the palaeo-anthropological community over whether Flo is truly representative of her kind, or merely a diseased individual with atypical characteristics. Flo's small head mimics a rare condition in modern humans known as microcephaly. But a recent and detailed examination of her skull suggests that the similarity is superficial. Further evidence against this idea comes from the discovery of at least five more diminutive individuals from the same spot where Flo was found. How likely is that they would all share the same rare pathology?

Animals that colonise islands often become giants or dwarves compared to their mainland relatives. The Galapagos has its tortoises, Mauritius had the Dodo, while the Seychelles has a frog no bigger than an ant. On Flores itself, there is that giant of the lizard world, the Komodo dragon, an extinct pygmy elephant, and an extinct species of giant rat. The forces underlying these evolutionary changes are still not properly understood, and the patterns often seem vague and unpredictable. But one general rule seems to be that large mammals get smaller, while anything smaller than a rabbit gets larger. Because islands have more limited resources, and contain fewer predators, a radical change in size may be the best way for a mammal to maximise its energy efficiency.

Whether this so-called 'island rule' can explain Flo's small stature is unclear. In mammals, selection for smaller bodies has only a marginal effect on brain size. But if Homo floresiensis descended from Javan populations of Homo erectus then Flo not only lost half her height, she also lost half her brain volume. Why would natural selection favour such a mammoth loss of grey matter? To answer that question we may have to wait for the next great fossil find.

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