February 17, 2011

Peeling Back the Layers of Palaeoanthropology

I took my first graduate-level human origins class a decade ago. Advances in DNA technology and the subsequent leap in our understanding of our hominin past in the last ten years mean that, as someone whose research focuses on anatomically modern humans, I sometimes feel overwhelmed by the pace at which palaeoanthropology is barreling forward.

For example, I last taught General Anthropology in the spring of 2009. Looking through my notes, I found that Neandertals and humans did not interbreed, based on research done by Richard Green at the Max Planck Institute for Evolutionary Biology. But in May 2010, Ed Green and colleagues at UC Santa Cruz reported that DNA analysis between the supposedly different species did indeed show commonalities - of at least 4%. This wasn't terribly surprising to me, as the morphological evidence, as championed by researchers such as Erik Trinkaus, has suggested that there might have been interbreeding between Neandertals and modern Homo sapiens. It was easy enough to incorporate this new finding into a lecture on hominin evolution.

But between December and February, suddenly a bunch of reports have arisen that call into question our understanding of modern human origins. First, there were news reports of Svante Paabo's genetic research on the so-called Denisovans, who shared genes with the Neandertals and ancestors of modern humans, specifically Melanesians. My understanding is that the Denisovans and Neandertals split off from a common ancestor and then evolved separately, and the Denisovans may represent a distinct wave of migration out of Africa. It was a bit difficult to explain to Gen Anth students the importance of the Denisova finds and even more difficult to explain just how much we don't know, or rather, just how many more questions the find raises.

Immediately after the lecture in which I incorporated this new discovery, on the day I was lecturing about when humans left Africa, a new study was published by Hans-Peter Uerpmann using evidence of tool manufacture to push back the date that anatomically modern humans left Africa by tens of thousands of years. Before I even delivered my lecture, some of the information in it was out of date. I tried to convey the excitement surrounding this new discovery but also talk about the potential drawbacks to using material evidence rather than anatomical evidence - or, better yet, both material and fossil evidence together - to make a claim for an earlier exodus from Africa.

This week has brought controversy over a paper published in Nature by Bernard Wood and Terry Harrison that suggests Ardipithecus may not be in a direct evolutionary line to Homo sapiens. Certain anatomical features that are often used to illustrate the unique anatomical and behavioral adaptations of hominins - centrally-placed foramen magnum and smaller canines - they argue could have been useful in other primates. Wood and Harrison suggest human evolution was more like a bush than a tree with distinct branches, which actually is not a new suggestion. Tim White takes issue with what Wood and Harrison's ideas mean for his Ardipithecus, namely that Ardi could have arisen through convergent evolution and isn't our direct ancestor. The news section at Nature has an interesting blog post about the controversy, including some choice words by White critiquing Wood and Harrison's ideas. Without the (current) possibility of using aDNA analysis to try to tease out evolutionary relationships this far back in time, palaeoanthropologists have to rely on what morphological features can tell us about our past. Just surveying the impact of DNA analysis on our understanding of Neandertals over the last two years, it's impossible to know when or even if the place of various hominin fossils in an evolutionary schema will ever be settled. Since I've moved on to archaeology in my four-field approach to teaching General Anthropology, I'm not going to revisit hominins and explain this newest issue to my students. They did get an earful already about the lumper/splitter debate, which I hope sunk in.

Today's palaeoanthropological news, though, did make me happy: Anthropologists Trace Human Origins Back to One Large Goat. The stalwart source for all fake news, The Onion, reports on their front page:

The landmark study culminates in this week's release of a 270-page report explaining the structure of prehistoric humans' short, upturned woolly tails and identifying the roots of early Indo-European† language in goat bleating, which, Ochs stated, "maybe [they] should have double-checked real quick" before the paper went to publication. [...] "Maybe we should have listened to Cliff [Geertz] back at the beginning when he kept emphasizing that humans don't look like goats," Hubbard-Price added.

As their colleagues huddled together and whispered behind them, researchers from Australia and Japan explained how one 6-foot-tall goat with a hominid skeletal structure spawned numerous goat-human hybrids over a period of 1.8 million years. In a series of PowerPoint slides, they then showed that our ancestors used their prehensile upper lips to perform basic agricultural tasks and stomped out crude pottery with their cloven feet, theories that team members stopped reading aloud to the assembled audience almost immediately after reaching the words "cloven feet."

"Okay, so I'm reading this now, and it says, 'After trotting out of Africa nearly 2 million years ago, our earliest ancestors used their strong hooves and hindquarters to climb up steep mountain slopes in search of delicious moss,'" said British anthropologist Oliver Cranmore, reading from the report and shaking his head. "The thing is, I think I actually wrote that part. And I remember feeling very confident and excited about it at the time. This is weird."
The Onion piece couldn't be more timely in its lampooning of our understanding of hominins. It's always dangerous to extrapolate from one fossil tooth or even a whole skeleton, but that's often as much as is available in the fossil record. I love learning about our origins as a species, and I try to keep up on the literature in spite of the pace at which research is moving ahead and in spite of the fact that it's not my particular research area.

I can only imagine how frustrating it is for students who want an introduction to human evolution to be confronted with ever-changing paradigms of development. The best I can do is what all teachers do - synthesize and integrate new research as it comes out - and to let my students know that, yes, the single-goat origin hypothesis will be on the midterm.

0 comments:

Twitter Delicious Facebook Digg Stumbleupon Favorites More

 
Design by Free WordPress Themes | Bloggerized by Lasantha