Convoluted human evolution: Asian contribution (Introduction)

by David Turell , Wednesday, July 13, 2016, 20:34 (3055 days ago) @ David Turell

As more fossils are uncovered in Asia, the story of human development gets more bushy:-http://www.scientificamerican.com/article/how-china-is-rewriting-the-book-on-human-origins/?WT.mc_id=SA_DD_20160713-" Palaeoanthropologists across the globe are starting to pay more attention to Asian fossils and how they relate to other early hominins — creatures that are more closely related to humans than to chimps. Finds in China and other parts of Asia have made it clear that a dazzling variety of Homo species once roamed the continent. And they are challenging conventional ideas about the evolutionary history of humanity.-***-"The tale is further muddled by Chinese fossils analysed over the past four decades, which cast doubt over the linear progression from African H. erectus to modern humans. They show that, between roughly 900,000 and 125,000 years ago, east Asia was teeming with hominins endowed with features that would place them somewhere between H. erectus and H. sapiens,-“'Those fossils are a big mystery,” says Ciochon. “They clearly represent more advanced species than H. erectus, but nobody knows what they are because they don't seem to fit into any categories we know.”-***-"Many researchers, including most Chinese palaeontologists, contend that the materials from China are different from European and African H. heidelbergensis fossils, despite some apparent similarities. One nearly complete skull unearthed at Dali in Shaanxi province and dated to 250,000 years ago, has a bigger braincase, a shorter face and a lower cheekbone than most H. heidelbergensis specimens, suggesting that the species was more advanced.-***- "Many researchers say that there are ways to explain the existing Asian fossils without resorting to continuity with hybridization. The Zhirendong hominins, for instance, could represent an exodus of early modern humans from Africa between 120,000 and 80,000 years ago. Instead of remaining in the Levant in the Middle East, as was thought previously, these people could have expanded into east Asia, says Michael Petraglia, an archaeologist at the University of Oxford, UK.-***-"A third idea is even more radical. It emerged when Martinón-Torres and her colleagues compared more than 5,000 fossil teeth from around the world: the team found that Eurasian specimens are more similar to each other than to African ones. That work and more recent interpretations of fossil skulls suggest that Eurasian hominins evolved separately from African ones for a long stretch of time. The researchers propose that the first hominins that left Africa 1.8 million years ago were the eventual source of modern humans. Their descendants mostly settled in the Middle East, where the climate was favourable, and then produced waves of transitional hominins that spread elsewhere. One Eurasian group went to Indonesia, another gave rise to Neanderthals and Denisovans, and a third ventured back into Africa and evolved into H. sapiens, which later spread throughout the world. In this model, modern humans evolved in Africa, but their immediate ancestor originated in the Middle East.-***-"Recovering more fossils from all parts of Asia will clearly help to fill in the gaps. Many palaeoanthropologists also call for better access to existing materials. Most Chinese fossils — including some of the finest specimens, such as the Yunxian and Dali skulls — are accessible only to a handful of Chinese palaeontologists and their collaborators. “To make them available for general studies, with replicas or CT scans, would be fantastic,” says Stringer. Moreover, fossil sites should be dated much more rigorously, preferably by multiple methods, researchers say.-"But all agree that Asia — the largest continent on Earth — has a lot more to offer in terms of unravelling the human story. “The center of gravity,” says Petraglia, “is shifting eastward.'”-Comment: Just as the Cambrian shale in China is adding much to our knowledge of evolution at that period, the renewed interest in Asian hominin fossils is showing that the human bush may be even bushier than imagined.