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March 03, 2005
The Hobbit's Brain Revealed but Don't Forget the Hobbit's Femur
Carl Zimmer at The Loom has a summary of a new study by Dean Falk, a Florida State University paleoanthropologist, and colleagues on Homo floresiensis brain using CT-scan. The bottom line: the "Hobbits" brain is closest to a Homo erectus brain but there are issues.
Of all the brains that Falk and co. compared to Homo floresiensis, Homo erectus came the closest--in particular, Homo erectus skulls from Java and China. They are also unusually wide, for example. But the Hobbit brain also has some strange features that set it off from Homo erectus. In some ways it is relatively primitive. For example, at the back of the Hobbit brain there is a relatively small occipital lobe. On the other hand, Falk and her colleagues noticed some traits in Hobbit brain that are more human-like. It has more convolutions at the front, for example, than Homo erectus. The temporal lobe, where hearing, memory, and emotions are handled, is enlarged, as well as the parietal association cortex, where some sensory information is handled. Perhaps most intriguingly, a region of the frontal lobes known as Brodmann's area 10 seems to be very large in the Hobbit. It is also large in living humans, and is known to be important in planning and other complex kinds of thought.
As Zimmer points out, one favored explanation involves H. floresiensis evolving from H. erectus. However, this explanation, as he says, has its problems. The H. floresiensis brain size as a function of body weight seems to match the great apes better than H. sapiens or H. erectus. This suggests that the Hobbit may have evolved from some smaller brained hominid rather than H. erectus or H. sapiens.
Here I leave Zimmer's account. A question that has bothered me involves the body mass of H. floresiensis. I've been trying to convince myself on this subject since the first announcement of the finds. The issue is how body mass should be calculated. Brown et la's 16 to 28 kg range of estimates are stature based and their higher, 36 kg estimate, is based on femur cross section. This gives a body weight range of 35 lbs to 80 lbs. Zimmer uses a low mid-ish number of 50 lb.
Now, if we look at encephalization quotients (EQ) and assume the estimated brain volume of 380 cm3 is correct, we get, as Brown did, an EQ range of 4.6 to 2.5 using Martin's formula. The high end of the range is good for a H. erectus while the low end provides good numbers for a chimp. So if the Hobbit's mass is calculated using the lower end of the body mass range based on stature one gets a perfectly fine H. erectus brain but if one uses the high end or the femur diameter one gets something like a chimp brain, at least in terms of EQ. If one uses the 50 lbs body mass, one gets an EQ of 3.6, at the very low end of the range for a H. erectus but pretty darn good for a chimp.
I believe much of this comes down to how we calculate and interpret body mass. I am working on a more extensive post on this question, which I hope to post soon (references and all).
Posted by DuaneSmith at March 3, 2005 03:08 PM | Read more on Paleoanthropology |
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