5.3.7 Regional Evolutionary Adaptations: Homo floresiensis

The Hobbit of Flores

Homo floresiensis, also known as “the Hobbit” or “Flores Man,” was discovered on the island of Flores in Indonesia in 2003. The species has been dated to approximately 100,000–60,000 years ago. What was surprising about this species is its size. An adult individual stood about 3 feet 7 inches tall. Liang Bua, the cave where H. floresiensis was found, shows evidence of the use of fire for cooking and contains bones with cutmarks. Since the initial discovery, partial skeletons of nine individuals have been found.

H. floresiensis, like the earlier hominins, did not possess a chin, and its leg bones are thicker than those of modern humans. They had flat feet that were relatively long in comparison to the rest of their bodies. As a result of these anatomical differences, it is believed that their bipedalism was quite different from that of modern humans, with a high stepping gait and slower walking speed. H. floresiensis also had substantially more mobility in the elbow joint, which suggests that they were tree climbers.

Their small brain size is not believed to have affected their intelligence. This challenges the view that larger cranial capacity equals higher cognitive skills. Although H. floresiensis has a brain size of just 380 cc, equal to the size of an orange, evidence indicates that they made tools, used fire, and hunted very much like H. erectus. The brain of H. floresiensis does contain a Brodmann area, which is associated with cognitive abilities, that is the same size as that found in modern humans.

Some have suggested that H. floresiensis is a sister species of Homo habilis that branched off before or shortly after the evolution of Homo habilis. Other hypotheses suggest that they were the descendants of H. erectus who became stranded on the island after arriving via water, possibly on bamboo rafts.

Another Homo species similar in size to H. floresiensis was H. luzonensis, found on the island of Luzon in the Philippines and dated to at least 50,000–67,000 years ago. H. luzonensis displays a hybrid of australopithecine traits (including curved hands and feet) and Homo characteristics, yet lived alongside modern H. sapiens. Clearly the genus Homo is more diverse and complex than was originally thought, especially within the special evolutionary pressures of island environments.

Island Dwarfism as an Evolutionary Explanation

Numerous hypotheses have been proposed to account for the small brain size found in both H. floresiensis and H. luzonensis. One initial theory was that H. floresiensis had microcephaly, which is a genetic condition creating an abnormally small head. This was discounted as an explanation once additional specimens were found exhibiting the same size. Perhaps the most convincing explanation is an evolutionary theory called island dwarfism, which notes that the evolutionary pressures on islands can be very different from those found on the mainland. Island dwarfism posits that mainland small animal species that colonize islands might evolve larger bodies if the island does not contain key predators. On the other hand, larger species may become smaller due to more limited resources in an island environment. According to the island dwarfism hypothesis, H. erectus made its way to Flores, where its descendants became isolated and grew progressively smaller to make the most of limited resources in the island environment. This theory is supported by the fact that there are unique sizes displayed by other animals found with H. floresiensis, including a dwarf species of primitive elephant called a Stegodon. As H. floresiensis’s body shrank, its brain may have undergone “neurological reorganization” to fit a smaller cranial space while maintaining its brain-to-body ratio. The only potential large predator that may have been a threat to H. floresiensis was the Komodo dragon, which ate most of the large mammals on the island. Nevertheless, predation pressures for the little people were likely quite low—that is, until H. sapiens arrived.