Homo floresiensis, a pygmy-sized small-brained hominin popularly known as 'the Hobbit' was discovered five years ago, but controversy continues over whether the small brain is actually due to a pathological condition.

How can its tiny brain size be explained? Researchers writing in the open access journal BMC Biology have tackled this question in the context of a comprehensive assessment of the evolution of brain and body size throughout the larger primate family.

According to Nick Mundy, "Our results provide robust confirmation for the suggestion that strong evolutionary trends have governed the expansion of the primate brain. In contrast, body size evolution has not tended to increase in primates, implying brain and body mass have been subject to separate selection pressures and supporting the findings of previous studies in other taxonomic groups that these two highly correlated traits can show differences in their patterns of evolution."

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.

"These are the skulls of Homo floresiensis (left) and Homo sapiens (right). (Credit: Professor Peter Brown, University of New England)"

Source: BioMed Central