Paper short abstract:

All over the world and in all time periods, animals on islands have adapted to their environment. In most cases, this meant a significant change in body size. Whether hominins conform to this 'island rule' will be assessed through comparisons with continental hominins and insular mammals.

Paper long abstract:

Evolution on islands differs fundamentally from evolution on the mainland. Unbalanced endemic island faunas lack mammalian predators. Due to a different (or even absence of) predation pressure, evolution can take a course not normally taken on the mainland, resulting in tiny elephants, small hippos and artiodactyls with the strangest head ornaments.

This presentation describes possible mechanisms driving island evolution and how these influenced insular mammal morphology. There are several key adaptations, which are seen in most island dwarfs. Most importantly, there is a reduction in size. This reduction is most pronounced in the limbs, with additional adaptations for 'low-gear locomotion', which minimises energy expenditure during locomotion. Additionally, reversals to an ancestral state take place for specific features, which is caused by a functional change for those features associated with the decrease in size.

An assessment of the morphology of Homo floresiensis is made in with respect to these typical adaptations to determine whether island dwarfing from H. erectus offers a plausible explanation for H. floresiensis or whether it is more likely that H. floresiensis descended from an australopith-like hominin. The brain of H. floresiensis is relatively small to lower its energy requirements. Its legs are relatively short and robust and its pelvis relatively broad as an adaptation to 'low-gear locomotion'. Furthermore, H. floresiensis displays archaic wrist bone morphology. The parallelisms with other island animals are so striking that the most parsimonious solution seems that H. floresiensis evolved from H. erectus in an island environment.

Dr Anneke H. van Heteren Netherlands Centre for Biodiversity Naturalis Research Associate