The brain endocast of 'Homo floresiensis': microcephaly and other issues...

Abstract

The discovery of a dwarfed hominid living under 20K ago, with a brain roughly 400 ml large, and associated with stone tools of Upper Pleistocene elements has led to considerable controversy regarding the hominid’s taxonomic position, possible pathology, and an opportunity to re-assess fundamental assumptions regarding the relationships between brains and behavior, particularly with regard to size. While the original Science paper by Falk et al (2005) provided an analysis ruling out pathology, namely microcephaly, the microcephalic endocast chosen was not a good representative of this spectrum of small-brained pathologies. With the cooperation of several colleagues, we have been able to study some 6 microcephalic endocasts, which represent the condition microcephaly vera, as well as Seckel’s syndrome. Our studies, while unable to rule out completely the possibility of brain pathology in the Flores Island hominid, suggests that none of the microcephalics studied thus far, including one measuring 400 ml, shares any patterns of pathology with the hominid endocast, unless the size alone is taken to be pathological. In addition, we find that the endocast volume is 400 ml, not 417 ml as reported in Science, and argue that features of the frontal and temporal lobes described as advanced may instead indicate some form of pathology (possibly microgyria). Gyri on the anterior frontal lobe do not match patterns seen in either normal modern humans, earlier Homo erectus, or in the microcephalic endocasts we have examined.