Insular dwarfism in hippos and a model for brain size reduction in Homo floresiensis

The Flores bones: primitive hominin retentions or insular dwarfing? The diminutive hominin Homo floresiensis, first described in Nature in 2004, lived on the island of Flores in Indonesia until about 14,000 years ago. The cover shows the partial skeleton of the type specimen, LB1. It preserves enough material to permit partial assembly of the foot, and that assembly is now reported by Jungers et al. LB1's foot had human-like fully adducted big toes, but they were longer relative to the rest of the lower limb than in modern humans, instead resembling some apes. The idea that H. floresiensis was a diminutive hominin met with some scepticism, in particular its small brain size was attributed by some to pathology. New work by Eleanor Weston and Adrian Lister shows that the brains of extinct dwarf hippos from Madagascar were disproportionately a lot smaller than those of their mainland relatives. This supports suggestions that island dwarfism breaks the 'rule' that body size reduction in mammals is accompanied by only a moderate reduction in brain size. In News & Views, Daniel Lieberman discusses these papers and a special issue of The Journal of Human Evolution, and concludes that H. floresiensis probably is a bone fide — and very interesting — species of hominin.