Sunday, July 13, 2014

RIP for a key Homo species?

Michael Balter
Science

Vol. 345 no. 6193 p. 129
DOI: 10.1126/science.345.6193.129   
(Link)
                     
Blog note:  If you don't have institutional access to Science, you can purchase the full text of this article for one day for $20 (yes, quite expensive for non-institutional access!)  In any case, here's the second half of the article, which concerns a concise synopsis of the current and still undecided status of the Homo species H. heidelbergensis:

"H. heidelbergensis has a history of controversy. The species is based on a single lower jaw found in 1907 at Mauer, near Heidelberg, in Germany. Estimated at about 600,000 years old, the jaw has an unusually thick ramus—the vertical projection that hinges to the skull—and nothing quite like it has been found since. For decades, the name failed to catch on, until anthropologists including Rightmire and Chris Stringer of the Natural History Museum in London noted distinctive thick brow ridges and large faces in skulls of roughly similar age from sites including Arago; Petralona in Greece; Broken Hill in Zambia; Yunxian in China; and Bodo in Ethiopia. All of these skulls also housed much larger brains than H. erectus, about 1200 cubic centimeters, within range of modern human brains, which average about 1400 cc. (Neandertal brains may be slightly larger.)

"In the 1970s, Stringer and others postulated a single species spanning Europe, Africa, and Asia, and resurrected the H. heidelbergensis name to describe it. The species' larger brain was reflected in the complex tools attributed to it, such as wooden spears at Schöningen in Germany (Science, 6 June, p. 1080).
                 
"Some researchers were skeptical, arguing that the African fossils were a separate species called H. rhodesiensis, which led to our ancestors. H. heidelbergensis got a big boost when researchers working at the site of Sima de los Huesos in Spain attached the name to the remains of 28 hominins found there. But in a paper last month in Science (20 June, p. 1358), the Sima team, led by Juan Luis Arsuaga of the Complutense University of Madrid, argued that these 430,000-year-old hominins were more closely related to Neandertals and don't belong in H. heidelbergensis.

"At the meeting, Arsuaga went a big step further and proposed eliminating H. heidelbergensis altogether. He argued that the Mauer jaw, the type specimen on which the species is based, cannot be closely matched with any other fossil, in part because few other jaws are preserved. To keep the species alive, researchers need to find and designate a new type specimen that has both a jaw and skull, but such a specimen would surely spark new debates, Arsuaga said. The better course “would be to let the species die.”
                 
"Anthropologist Yoel Rak of Tel Aviv University in Israel supported this argument by comparing the Mauer jaw with the few jaws claimed to be H. heidelbergensis fossils, including three partial jaws from Arago. “The Mauer specimen is one of a kind,” Rak concluded in his talk.
                 
"But others fought vigorously to save both the species and the simpler, more straightforward view of human evolution that it represents. Rightmire analyzed 34 H. erectus and 11 potential H. heidelbergensis skulls, and found that their similarities—including massive brow ridges, large faces, and flattened frontal bones—stemmed from true relatedness, rather than convergent evolution. “Calling them H. heidelbergensis is the correct position,” he said.
                 
"And paleoanthropologist Ian Tattersall of the American Museum of Natural History in New York City argued that the Mauer jaw isn't so singular after all: He found close affinities between it and the Arago jaws, especially in the teeth. Specimens from Arago preserve both the face and jaws, Tattersall notes, and the face resembles those of other claimed members of H. heidelbergensis, thus completing the link between the type specimen and skulls from several continents.
                 
"New fossils from this mysterious time period would help. At the meeting, paleontologist Berhane Asfaw of the Rift Valley Research Service in Addis Ababa offered a rare glimpse of new finds from Ethiopia's Middle Awash region. His team has found partial skulls and jaws from 32 hominin individuals, roughly dated by animal bones to 300,000 years ago. These as-yet-unpublished fossils may link the Bodo skull from Ethiopia, which resembles Arago, and modern human skulls from the Middle Awash site of Herto. Expect fresh debate when these key fossils make it into print."

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