Brain expansion began early in primate evolution and has occurred in all major groups, suggesting a strong selective advantage to increased brainpower in most primate lineages. Despite this overall trend, however, Mundy and his colleagues have identified several branches/lineages within each major group that have shown decreasing brain and body mass as they evolve, for example in marmosets and mouse lemurs.
According to Mundy, “We find that, under reasonable assumptions, the reduction in brain size during the evolution of Homo floresiensis is not unusual in comparison to these other primates. Along with other recent studies on the effects of ‘island dwarfism’ in other mammals, these results support the hypothesis that the small brain of Homo floresiensis was adapted to local ecological conditions on Flores.”
The paper will show up in BMC Biology at some point. The main question I have is in regards to the purported tool use of the Hobbits. I can believe that a local adaptation toward small brains, Idiocracy-writ large, occurred. Brains are metabolically expensive, and it isn’t as if the history of life on earth has shown the massive long-term benefits of being highly encephalized (though I think one can make a case that there has been a modest trend, with primates, and especially H. sapiens as extreme outliers above the trend). But could small brained creatures maintain the relatively advanced toolkit which the Hobbit finds have been associated with? Seems to me that there’s a high probability here of some sort of contamination, but I’ll be happy to be put in my place by anthropologists in-the-know….