WASHINGTON (March 3, 2005) –The first detailed study of the brain of Homo floresiensis — the tiny human relative that scientists have nicknamed “hobbit” — shows anatomical features consistent with higher cognitive processing such as taking initiative and planning ahead.
Homo floresiensis is a new species of human whose 18,000-year-old fossils were found on the Indonesian island of Flores; its discovery was announced last October by an Australian-Indonesian team. The new human’s sloping forehead, arched brow ridges and nutcracker jaw resemble those of the human ancestor known as Homo erectus, but its size is miniature. Its brain is one-third the size of a contemporary human’s.
Now Dean Falk, professor of anthropology at Florida State University, has led a team that created the first virtual endocast of the tiny human’s diminutive braincase — a reconstruction using three-dimensional computed tomographic technology to reproduce details of the external surface of the brain. Her work was funded by the National Geographic Society.
Among other discoveries, the team found that the Homo floresiensis brain’s frontal lobe, an area thought in humans to be involved in higher thinking processes, contains significant swelling, and the temporal lobe, where functions such as memory and emotions are processed, appears enlarged, and thus possibly more advanced.
The results of the study are reported in the March 3 issue of Science Express, the online version of the journal Science. Authors are Falk; Charles Hildebolt, Kirk Smith, Barry Brunsden and Fred Prior of Washington University’s Mallinckrodt Institute of Radiology; M.J. Morwood and Peter Brown of the University of New England in Australia; and Thomas Sutikna, Jatmiko, and E. Wayhu Saptomo of the Indonesian Centre for Archaeology.
The study of the hobbit brain will be featured in a special edition of Explorer on the National Geographic Channel on Sunday, March 13, at 8 p.m. ET/PT. (Check local listings.)
Falk and a team at the Mallinckrodt Institute used CT data gathered in Indonesia from the Homo floresiensis skull to create the virtual endocast of the creature’s braincase. From a physical model of the skull, Falk also made a physical endocast out of latex to further her analysis. Falk has been creating physical endocasts for 30 years.
The virtual endocast process reproduced details of external brain morphology, including sulci (brain grooves), vessels, sinuses, cranial capacity and shape, which were imprinted within the living creature’s braincase. The team then compared the hobbit’s endocast to those of an adult female chimpanzee, an adult female Homo erectus, a contemporary woman, and a microcephalic (human with an abnormally small skull). Female specimens were chosen because the original Homo floresiensis specimen was determined to be a female.
To broaden the study, Falk’s team also compared the hobbit endocast with those from skulls of two early hominins, Australopithecus africanus and Paranthropus aethiopicus, as well as 10 humans, 10 gorillas, 18 chimpanzees, an adult female pygmy and five Homo erectus specimens.
Although the Homo floresiensis brain is the size of a chimp’s, Falk said its appearance immediately reminded her of that of Homo erectus, the human ancestor that arose around 1.8 million years ago and is known to have lived in Africa, Europe and Asia. “It was a surprise because the brain was so small that we thought it would resemble a chimp’s, but instead it was much more like that of bigger creatures,” Falk said. Homo erectus has a brain with a signature shape, she said.
To address suggestions that the creature was actually a Homo sapiens individual suffering from microcephaly, the team compared the endocast to that of a microcephalic and found numerous inconsistencies. In fact, of all the endocasts the team compared to Homo floresiensis, the microcephalic’s was the least similar. “Homo floresiensis is not a microcephalic,” Falk said.
Similar disparities were found with endocasts of a human pygmy, chimps and gorillas.
Falk and the team report that the Homo floresiensis brain has its own suite of specific advanced and primitive features, a combination that has not been seen before. They observed these advanced features:
●In humans, the back of the brain in the region of the parietal association cortex contains processing areas for sight, hearing and touch, among other functions. In LB1 (the museum reference number for the H. floresiensis specimen), this area may have been organized along human lines, indicating possible advanced development.
●The temporal lobe, the mid-brain area between the ears where such functions as hearing, memory, image identification and emotions are processed, appears enlarged in LB1’s endocast.
●The part of the frontal lobe directly above and between the eyes, known as Brodmann’s area 10, is thought in humans to be involved in higher cognitive processes, such as the undertaking of initiatives and planning of activities. This region contains significant swelling in Homo floresiensis. “That’s special — you don’t see that anywhere else,” Falk said.
The brain of Homo floresiensis also presents some primitive features, the scientists found. Its pint size may be considered primitive, and its occipital lobe, in the back part of the brain, is not as expanded as that of Homo erectus.
Falk says the brain study supports the notion that Homo floresiensis is indeed closely related to Homo erectus yet is its own human species. The Science paper supports the suggestion that the species either evolved directly from Homo erectus in a case of island dwarfing — a response to the limited food supply on the small island of Flores — or that Homo erectus and Homo floresiensis shared an unknown, small-bodied and small-brained common ancestor.