Genética quantitativa evolutiva e o tamanho do cérebro em Homo floresiensis

Abstract

In 2004, a new species of the genus Homo (H. floresiensis) from Late Pleistocene of Indonesia (Flores Island) was described based on parts of an adult female skeleton about 1 meter tall and brain size about 400 cm3. The new species was interpreted as a case on miniaturization of body and brain sizes due to occupation of an island habitat (the "island rule"). Although there is some discussion about the identification of the material (some argue that it belongs to a microcephalus H. sapiens), some recent studies on brain anatomy validated the material as a real new species. In this paper we applied quantitative evolutionary genetic models to evaluate reduction in brain size of H. floresiensis from an ancestor H. erectus population under island rule, assuming various times for divergence between these species. Under the most conservative scenario (about 100,000 years of divergence, or 10,000 generations), brain size evolved at 9.16 darwins, with an intensity of selection equivalent to 0.096% of selective mortality. Evolutionary rates similar to those calculated for phenotypic evolution in post-Pleistocene mammals were observed when assuming divergence times about 250.000 years. Thus, brain size reduction in H. floresiensis under island rule would be plausible, even in a very conservative scenario of recent divergence between the species and its ancestor.