Saturday, May 9, 2009

Hobbit Brain explained by Hippo

The hobbit is the common name for Homo floresiensis, a 1-m tall human. Studies of extinct Madagascan hippos by the Natural History Museum may reveal the origins of the hobbit's small cranial capacity. The reason reported is that both hippo and hobbit were island dwellers! The hobbit lived on the Indonesian island of Flores. The team of investigators believe that after the hobbits' ancestor, Homo erectus, became isolated on the island of Madagascar, the hobbit became a dwarf in all senses of the word, physically and mentally... I wonder if small cranial capacity/brain corresponded with decreased cognitive abilities? What's interesting is that this seems to be backward evolution! Rather than proceeding in the direction that eventually gave rise to Homo sapiens, evolution seemed to have taken a "regressive" path. However, this finding fits quite well into my new discovery of the term, ecotype as mentioned in my observations for the week. Perhaps dwarfism allowed better adaptation to the niche in Madagascar. Also, there are plenty of branching events in evolution that may eventually lead to extinction; this serves to remind us that evolution turns a blind eye to so-called "progress". It does not necessarily always choose the most efficient, supposedly adaptive path.
The hobbit's brain is about the size of a chimp brain. The Madagascan hippo may have evolved small brains for its big size for the same reasons as the hobbits. However, the hippo brain used for analysis comes from a 3000-year-old extinct Madagascan hippo. Perhaps the resource limitations on islands and the fact that the brain consumes tons of energy partially explain the adaptation of smaller brains. It would be interesting to investigate any indigenous peoples left in the world who still live in primitive conditions on islands. Perhaps any similarities between their brain size and the hobbit's will better justify the new observation that brain size shrinks with habitation on islands. I wonder if the smaller evolved brain size eventually became a bane for these organisms' survival and thus although being adaptive initially, eventually led to their extinction as bigger brained descendants took over.
Interestingly, domesticated animals also have been reported to have smaller brains than their wild counterparts. However, the decrease in brain size of domestic mammals is not necessarily associated with decrease in body size. Although many confounding variables are present with variations and correlations between brain and body size in domesticated animals (i.e. less stimulation, enrichment in environment can possibly retard brain growth), perhaps domesticated animals in their insular settings can shed some light on any more extreme shrinkage of brain size compared with general dwarfism of the body.

-Bonnie Chien

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