How did humans evolve? Taiwan fossil complicates picture.

Found sitting at the depths of a submarine channel off the shores of Taiwan, a recently discovered fossil may add another small piece to the puzzle of how humans evolved.

The fossil, a partial jaw with still­-attached teeth, is the first of an ancient hominin – a member of a taxonomic group that includes the genus Homo and its extinct relatives – found in Taiwan. And by exhibiting subtle differences between characteristics of the uncovered fossil and others located across the region, the discovery may provide further evidence that a variety of human lineages existed in eastern Asia thousands of years ago.

Mapping human evolution is a messy process. Some paleontologists argue that ancient humans with even apparently small differences, from jaw size to the shape of the skull, deserve to be counted as distinct species or sub­-species. Others point out that humans today exhibit a wide range of head shapes and facial characteristics, but that these distinctions hardly make us separate species. To add to the confusion, bones or artifacts that have been sitting underground or deep in the ocean for thousands of years can be extremely difficult to examine. In the case of the Taiwanese fossil, scientists have been looking at it for four years, and many questions about it still remain.

The researchers didn't come upon the fossil on their own. A fisherman, who dredged it off the western shores of Taiwan, sold it to a local antique shop. Mr. Kun-Yu Tsai, a local collector, then bought the fossil.

"I know well about those kinds of collectors in south Taiwan," Chun-Hsiang Chang of the National Museum of Natural Science in Taichung, Taiwan tells the Monitor. "When I saw the fossil in 2008, I knew it is an unusual and important fossil."

Chang and his team of international researchers were able to date the relic to the Pleistocene era, which lasted from about 2.5 million years ago to 12,000 years ago. Dubbed Penghu 1 by the researchers, the jaw's owner lived between 190,000 and 10,000 years ago.

What they have yet to determine is whether or not Penghu 1 should be considered a member of a distinct species.

"Despite the fact that Taiwan is an island now, the size of the new mandible is not very different from other archaic hominins from the mainland," says Chang.

Scientists already have evidence for a variety of ancient human populations that once lived in the region. Homo erectus, which is thought to have survived the majority of the Pleistocene era, has been found in China and the Indonesian island of Java. Remains of Homo floresiensis, nicknamed 'hobbit' for its small stature, came from Flores island in Indonesia. And evidence of Neanderthals and Denisovans, Homo species that interbred with one another and with H. sapiens, have been found in the Altai mountains of Russia.

And now with the discovery of Penghu 1, there is evidence that even more diversity existed. Though the Penghu 1 fossil shows similarities to Homo erectus, it maintains a unique morphology compared to humans of several regional groups within Homo erectus. Prior to Chang's locating this fossil, there had only been one discovery of an ancient human with similar morphology in the entire region - in the Hexian district of southeastern China. 

"The new specimen is informative enough to conclude its differences from the known hominin fossils except for those from Hexian," says Chang.

So Chang and his colleagues are proposing that Penghu 1 and the ancient human from Hexian may represent a separate regional group. But, according to Chang, the study of the Penghu 1 fossil is the beginning of a long process to prove their hypothesis.

"This is a significant find and we are now sure that a previously unrecognized hominin group was once there," says Chang, "but we need more fossils to know more details about this newly recognized group."

The findings were published Tuesday in the journal Nature Communications.