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One of the goals of my courses is to equip students to evaluate and understand the importance of future discoveries in human evolution. This week, I was able to end my course with a review of new research from just the past week. 
The Hualongdong fossil material from Anhui province, China, represent a population that lived between 331,000 and 275,000 years ago -- the same time as early Homo sapiens and Homo naledi in Africa, and Neanderthals and Denisovans in western Eurasia. doi.org/10.1073/pnas.1…
This is a time after Zhoukoudian, Hexian, and other "Homo erectus" fossil material from China, and before any evidence of modern humans. Once, paleoanthropologists tried to shoehorn the Chinese record into a European framework, even calling some fossils "Homo heidelbergensis".
As Xiujie Wu and coworkers showed this week, the Hualongdong fossils (like others from this time period) have a mosaic of traits shared with both earlier and later Chinese populations, and even a few that have been associated with Neanderthals and modern humans.
What the Hualongdong material doesn't much look like is the mandible reported this week by Fahu Chen and coworkers, from Xiahe, China. This specimen, from the eastern Tibetan plateau, shares a collagen signature with specimens from Denisova Cave, Russia.
The Xiahe specimen was found in 1980 by a monk, reported to scientists, but without good context it was hard to do anything further. Until the development of better U-series dating methods and proteomic approaches.
Based on carbonate encrusted on its surface, the mandible is at least 160,000 years old. That extends human occupation of the high-altitude Tibetan plateau by another 120,000 years.
The Xiahe mandible doesn't much look like contemporary material from further east in China. It does look a good bit like a specimen dredged from the Taiwan Strait and reported in 2015 by Chun-Hsiang Chang and coworkers. doi.org/10.1038/ncomms…
Yes, scientists are now able to study a few specimens dredged from areas now under the sea that were dry land during the last glaciation. Our understanding of human origins is biased by sea level changes, a bias that has led to huge mistakes about the abilities of ancient people.
Here's another discovery revealed this week: Bonobos had a contribution from a previously undiscovered ancient ape population: A ghost ape!
Geneticists now can examine living species for evidence of mixture from others no longer represented by samples from living populations. The Denisovans had such mixture, as did living African peoples, from unknown ancient hominins. Many ghosts in other species.
Martin Kuhlwilm shares the story of finding the bonobo ancient admixture. It's a cool story that shows how today's populations do not represent the diversity of past populations. natureecoevocommunity.nature.com/users/255308-m…
For my course, the great thing is that we reviewed bonobo-chimpanzee genetic hybridization and historic mixture in the first few weeks. The "ghost ape" is a logical prediction, and here it is.
We have hardly any fossil record of chimpanzees and bonobos. A tiny handful of Middle Pleistocene-era fossil teeth from Kenya appear to represent ancient chimpanzee relatives from more than 500,000 years ago. doi.org/10.1038/nature…
These ancient chimpanzee fossils from the Kapthurin formation, reported by Sally McBrearty and Nina Jablonski in 2005, lie outside of today's geographic range of chimpanzees and bonobos. Today's eastern chimps didn't separate from other chimps until the last 100,000 years.
Today's eastern chimpanzees, Pan troglodytes schweinfurthii, were a dispersal that unfolded around the same time as modern humans dispersed from Africa. My guess is that these ancient chimpanzee fossils may be the ghost ape.
Another discovery revealed this week: A possible human footprint from Pilauco, Chile, which at an estimated 15,600 years would be the oldest in the Americas, and possibly the oldest dated evidence of humans in the Americas. doi.org/10.1371/journa…
Some people might say that such new discoveries are filling in missing details from the chapters of the story of human origins. But this is a false metaphor. Human evolution is not a story with a beginning, middle, and end. It is a diversifying and reticulating tree.
Our fossil and genetic sample of this tree is increasing greatly. But it is still a sparse sample. Sometimes new discoveries, like the Xiahe mandible, will confirm hypotheses based on earlier finds. But even those usually raise new mysteries.
I come back to the gap of 120,000 years between the minimum age of the Xiahe mandible and the oldest previously-known archaeological material in Tibet. What else is missing in the holes of our understanding? We don't know. But we can explore.
Did my course accomplish its goal over the semester? On the last day, students came in asking about the new research. That’s a great start!
