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Alien From Earth

Compare the Brains

Who was the so-called Flores hobbit, the three-foot-tall, 18,000-year-old skeleton found in Indonesia in 2003? More precisely, what was she? Was she a tiny descendant of Homo erectus? A modern human dwarfed by disease or genetic defect? Or a new species entirely, as its discoverers proposed, giving it the name Homo floresiensis? Paleoanthropologists and other experts are still trying to answer these and other basic questions about this diminutive creature (including whether the skeleton belonged to a male rather than a female, as originally reported). One of the most highly regarded attempts to determine the hobbit's true ancestry was undertaken by Dean Falk of Florida State University and colleagues, who used computers to compare the size and shape of the hobbit's brain with those of a modern human, a Homo erectus, and other members of the great-ape line.* Below, see how the hobbit's brain measured up—and the novel conclusion that Falk's team reached.—Peter Tyson & Rachel VanCott

*See Falk, D. et al., "The Brain of LB1, Homo floresiensis." Science 308, 242-45 (2005).



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The study
Dean Falk's team, which included Charles Hildebolt of the Mallinckrodt Institute of Radiology in St. Louis and several others, created a virtual endocast, or computer model, of the hobbit's brain (left). They used CT scans made of the skull shortly after its discovery. (The hobbit's skull and other bones are not fossilized and extremely fragile, making the standard method of making endocasts—pouring liquid rubber into the skull—not feasible.) They then compared the hobbit's virtual endocast with those of a modern woman, a Homo erectus, a chimpanzee, and a modern microcephalic (a person with an abnormally small head).




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LB1
The hobbit skeleton is known as LB1, for the cave where it was found, Liang Bua (Cold Cave). The team's measurements revealed that LB1's brain was as small as that of 3.2 million-year-old "Lucy," or about the size of a chimp's. (See Who's Who in Human Evolution for more on our rich evolutionary history.) But LB1 was associated with charred bones, stone tools, and remains of Stegodon, a now-extinct dwarf elephant, suggesting her kind knew how to use fire, cook, and hunt. How could a tiny hominin with a chimp-sized brain have had such advanced behaviors? Comparing brains, the team decided, might help provide an answer. (At left, LB1's skull.)




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LB1 and Homo sapiens
After LB1's discovery, some scientists had suggested that the hobbit was really a modern human, just a small one. But when Falk's team measured the brains of LB1 and Homo sapiens, they confirmed what seems obvious to the eye—the two brains are very differently shaped. In addition, LB1's body-size-to-brain-size ratio doesn't match that of a human dwarf. When H. sapiens bodies shrink, the brain and head stay relatively large. That's not the case with LB1—her brain and head are small in proportion to her body. LB1's brain also bears little resemblance to that of a human pygmy, the team noted.




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LB1 and microcephalic Homo sapiens
Was LB1 perhaps a modern human with a pathologically small brain, one deformed by illness or genetic defect? No, say Falk and her colleagues. LB1's endocast indicates her brain fit snugly in her skull, and parts of her brain are highly convoluted, or intricately folded. By contrast, microcephalic brains rest loosely within the braincase and create endocasts that lack detail, like the one seen here. (Some experts, including Robert Martin of Chicago's Field Museum, say the team's sample size of one microcephalic skull was too small, and they still hold with the modern microcephalic hypothesis.)




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LB1 and Pan troglodytes
And how did LB1's brain compare to that of a chimpanzee? While the two brains are about the same size, they differ dramatically, the team found. LB1's has large temporal lobes, which in people are linked to hearing and understanding speech. More significantly, LB1 has highly convoluted frontal lobes, the region just behind the forehead that is associated with higher cognition. Altogether, the findings support the notion of advanced intelligence in a small package. This flies in the face of current dogma, which maintains that increased intelligence only comes through increased brain size.




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LB1 and Homo erectus
At a glance, LB1's brain looks much like that of a shrunken H. erectus, the extinct hominin best known by the Java Man specimens. Indeed, the two brains are similar in height and width, and both have a recognizably low, long lateral profile. To some experts, such a similar shape strongly suggests an evolutionary connection. But Falk's team does not believe the hobbit was a miniaturized descendant of H. erectus. Its cranial capacity was simply too small to be attributed to normal dwarfing of H. erectus, they say.




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LB1 a new species?
LB1's similarity to H. erectus, which is thought to have arrived on Flores by 800,000 years ago, led Falk and her colleagues to an original conclusion. While it is possible, they say, that H. floresiensis was a dwarf species of H. erectus unique to Flores, they offer an alternative hypothesis. H. floresiensis and H. erectus, they suggest, may have shared a common, currently unidentified ancestor, one that had a small brain and a small body. About all anyone seems to agree on is that the hobbit is a fascinating new addition to the puzzle of human origins and that more work, including DNA studies, may help clarify things.



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