Scientific American has new information on very old remains of Homo floresiensis, the diminutive prehistoric humans who lived on the island of Flores around 700,000 to 60,000 years ago. A newly discovered arm bone from some of the first humans on Flores show that the so-called “hobbits” grew smaller over the 100s of millennia they stayed on their small island:
Researchers have argued about whether it arose from an already small, primitive early human, such as Homo habilis or an Australopithecus species, or from a bigger-bodied, larger-brained H. erectus that shrunk under the pressures of island life. A third argument that was taken off the evolutionary table was that these were modern humans with a condition that caused dwarfism.
In 2016 scientists unveiled a lower jaw fragment and small teeth that appeared to belong to a more primitive H. floresiensis at the site of Mata Menge, about 70 kilometers from the Liang Bua site on Flores. These fossils, which came from at least three individuals, dated back 700,000 years, well before modern humans emerged anywhere on Earth. (The oldest fossils from an anatomically modern human date to around 315,000 years ago in what is now Morocco.) The researchers argued that similarities between those tooth and jaw remains suggested that a larger hominin (a member of a group containing modern humans and their extinct relatives), possibly H. erectus, traveled from the Indonesian island of Java and got stuck on Flores, where it evolved smaller proportions, eventually giving rise to the tiny H. floresiensis.
Researchers led by Yousuke Kaifu of the University of Tokyo recovered the new arm bone—an incomplete humerus measuring just 8.8 centimeters long—from Mata Menge, along with some additional teeth.
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Importantly, all the Mata Menge remains are small. The teeth mandible and humerus are all smaller than those found at Liang Bua, Kaifu says. “This means that, 700,000-years-ago, Homo floresiensis was at least as small as, or even slightly smaller than, the 60,000-years-ago Homo floresiensis from Liang Bua,” he adds.
The findings suggest that “once a population of Homo erectus got stranded on Flores one million years ago, there was no more genetic exchange with mainland hominins, and the large-bodied Homo erectus evolved to the smaller Homo floresiensis by a process called insular dwarfing,” [University of Wollongong researcher Gerrit] van den Bergh says. The same seems to have occurred for Flores’s animals, such as dwarfed species of Stegodon, ancient relatives of elephants: because of food limitations, lack of predators and the loss of the need to search long distances for such food (which is aided by being bigger), creatures shrunk, the thinking goes. Van den Bergh adds that H. floresiensis’ body size could have fluctuated over time because of changing climate and environmental conditions. The species vanished from the fossil record at about the same time that modern humans appeared on the island, about 50,000 years ago.