Flores Hobbit's Brain Size Larger Than Thought, Increases Chances of Homo erectus ancestry

Diseased ancestor or mini-me? The debate over where the so-called "hobbit," or Homo floresiensis, came from has raged since researchers discovered its remains on the remote Indonesian island of Flores in 2003. Some researchers said its diminutive size was the result of disease, while others believed it descended from a small-bodied human ancestor.

But a new study, published April 17 in the journal Proceedings of the Royal Society B, says that clues to the hobbit-like human's ancestry lies in the size of its brain. The hobbit's gray matter is actually slightly larger than previously thought, according to the study's authors.

The so-called hobbit, which stood three feet (one meter) tall, lived on Flores until approximately 17,000 years ago. Previous studies examining H. floresiensis's skeleton ruled out the possibility of a disease called microcephaly as the cause of its small stature.

But if it was a new species of human, who was its ancestor?

Dwarfism?

One possibility is that the hobbit evolved from another small-bodied, small-brained early human, or "hominin," called H. habilis. The main problem with this theory is that there is no evidence that H. habilis ever made it to Southeast Asia, let alone Flores. (Explore the human evolutionary highway in this interactive.)

Other researchers have argued that H. floresiensis is descended from the larger-bodied H. erectus, widely considered to be the first hominin to leave Africa. Remains of H. erectus have been found throughout Asia, including on the Indonesian island of Java.

According to this hypothesis, H. erectus somehow made its way to Flores, where its descendants shrunk in size through a process called island dwarfism, in which species grow smaller to make the most of limited resources. (Related: "'Hobbits' Had Million-Year History on Island?")

"Some recent [animal] examples suggest that island dwarfism may be a fairly rapid process, [occurring] within a few thousand or even a few hundred years, but each case may be different," said study coauthor Yousuke Kaifu, a senior researcher at the National Museum of Nature and Science in Tokyo.

But critics of this theory have argued that the brain size difference between H. erectus and H. floresiensis—991 cubic centimeters (cc) and about 400 cc, respectively—represents an extreme and unprecedented example of island dwarfism. For comparison, modern humans have an average brain size of about 1,300 cc.

"Many recent researchers apparently suppose this is impossible," Kaifu said in an email.

Plausible Differences

But in their new study, Kaifu and his colleagues showed that the size gap is actually smaller than previously thought. Using a new high-resolution CT scanning technique, the team created a 3-D model of an 18,000-year-old H. floresiensis skull and calculated its brain volume to be about 426 cc.