Can the discovery of one hominin skull truly revolutionize our understanding of human origins? This critical question is often overlooked in the media’s use of sexy language and bold stories of rising tensions, which allure wide audiences into compelling and sensational stories. Just a few short days ago I was reviewing student posts from a class on human origins when I received a message from a friend asking for my input on the discovery of a new Homo Erectus skull from Dmanisi, in southern Georgia. “What are your thoughts on this?” my friend asked.
Being a daily reader of BBC, NYtimes, and Discovery science sections I was surprised I hadn’t yet heard of this ‘new’ discovery. The name Dmanisi, however, did make me pause. The skull that was found back in 2005? A quick Google search revealed this particular paleoanthropological discovery is indeed new and is the fifth well-preserved skull to be recovered from the area.
It didn’t take long to see the impact of the discovery in the media, on message boards, or social networks. My friend’s initial question, posted on Facebook, had already received a series of comments and shares ranging from pure fascination to a sense of mild shock and disbelief. Similarly, CNN, BBC, Discovery and any other news site with a scientific interest were showcasing this as a headline story. Extra, extra, read all about it! New fossil shatters the story of human evolution!
What was so earth shattering about this story though? It certainly isn’t about another missing link between humans and apes. I’m biased here. I love the subject and have been a teaching assistant in a class focused on just this subject for years. When a finger bone was found in 2010 with DNA identifying a potentially different species of hominin from our own genus Homo, I was exited. Let’s be real, I was giddy. The implications were making a cool sci-fi story come to life for me and this happens every time there is a new discovery of a human ancestor.
The media shared in my excitement. Headlines ranged in claims from human ancestry being thrown into ‘disarray,’ ‘sparking controversy,’ and declaring it’s time to ‘rethink human evolution.’ The actuality here, however, doesn’t really differ or deviate from expectations in the field. The hypotheses put forward by the researchers stem from the evidence that Dmanisi skull 5, a Homo Erectus skull, and the four other associated skulls, exhibit a wide range of variation. The skulls look remarkably different and are believed to be from the same species. This line of evidence lead a group of researchers to suggest the human evolutionary tree is not as bushy as it was once believed to be. While this thought is really cool, it isn’t new.
In some ways this discussion dives back into two theoretical extremes, which have a tendency to occasionally butt heads in a feud whenever a new fossil discovery is made (lets say once every year and a half or so). After the skirmish, the two theories often shake on a tentative compromise, which often leans in the direction of one more than the other. What I’m talking about are the “Out of Africa” and “Multi-regionalism” theories.
In a nutshell the former says, I think modern humans all came out of Africa around the same time and populated the world looking for tasty snacks and adventure. The other theory thinks people kind of did there own thing in isolation everywhere, sharing a common ancestor with something. Then they got board and left home for adventure and new tasty snacks. These two ideas are hypotheses. This means they need to be tested, holes need to be poked in them, and new compelling ideas need to emerge victorious from the ashes and continue the cycle.
There is a small problem in this. Really big discoveries don’t happen very often. In fact, in the field of paleoanthropology, just about every discovery is a big discovery. If one were ambitious enough to pile every bone of a possible modern human ancestor into a football stadium, there would be plenty of left over seats and that game would probably be blacked out. On the other hand, one could certainly take fantastic photos of these specimens and make a really nice coffee table book.
At its root, the problem is that we don’t have enough comparative fossil data to work from. What we do have may not even be representative. Bones do not preserve well if unattended. Making matters worse, many of our early ancestors were not the predators but scavengers that doubled as prey. To be preserved, you need a lot of luck to die in a place with the perfect conditions while being fortunate enough that nothing scavenges you. This means places like caves, riverbeds with silty sediments, or a healthy coding of volcanic ash are among the best for preservation. Typically, this doesn’t happen very often. As a result, we tend to look for fossils in places where the conditions were right in the past, and where the conditions are right today. This means caves, rift valleys (areas where the earth has opened up and placed fossils on the surface for us), and where political environments are safe and accommodating.
Now that that is out of the way, change happens frequently in the field as one new discovery provides a new specimen to a small supply. Drastic change in this field also happens, but not nearly as frequently because of the issues above. Back to the “Out of Africa” or “Multi-regionalism” debate, the five Dmanisi skulls, showing significant variation, have been taken to suggest that previous discoveries and classifications of other potential species of human ancestors in the Homo genus (such as H. Habilus, H. Rudolfensis, and H. Ergaster) are actually all the same. They’re all H. Erectus. The claim is that the Dmanisi H. Erectus individuals turned our understanding of a wide and bushy tree of descent into a relatively straight line. If only things were that easy.
Modern Homo Sapiens Sapiens are polytypic, meaning we look drastically different from one another. If you walk to a dog park and pick the first two dogs you see, say a Shih Tzu and a German Shepard, they look different but are very much the same species. Dogs are polytypic. If you walk into a jaguar reserve in Belize and compare the first two jaguars you see, you are much more unlikely to be able to tell them apart. Jaguars are less polytypic.
Humans have a wide array of different skull forms and sizes. Anthropologists can attest to this, as the field got much of its early start by comparing the shapes and sizes of skulls from people of different populations. In saying that, there is no reason why the skulls of our direct ancestor, H. Erectus/H. Ergaster, shouldn’t show the same variation over a wide geographic distribution (also a wide range of different adventures and tasty snacks). Bearing that in mind, the differences could be significant if we had information as to how those differences were being expressed. Modern human variation occurs on a cline (think incline or a curve on a graph), meaning that on two polar ends of the spectrum, variation is very significant. Yet, there is continuous variation between the extremes accounting for the drastic differences at each end.
In order to be sure, we’d need to see how and when the different H. Erectus/H. Ergaster/ H. Rudolphensis/ H. Habilus skulls are distributed. Time and place are very critical, as closer to 2 MYA the skull traits should be more primitive, having recently separated from the Australopithecine genus. Skulls from 1 MYA (and more recent) will show more derived characteristics. As for the idea that H. Erectus/H. Ergaster/ H. Rudolphensis/ H. Habilus could be the same, that really just depends upon who is making the taxonomy. Lumping versus splitting. That argument is very old. As much as this skull changes things (by adding another variation to account for) and is a great cause for excitement in the field, the argument is not new or revolutionary.
Yet, we shouldn’t forget how alluring new discoveries are.
Paleoanthropology is one of the few fields in which any person can make a huge discovery about our collective social past. Just take the young boy, Matthew Berger, who stumbled across Australopithecus Sediba (a possible human ancestor) in 2008, with his father outside of Johannesburg. No matter how small the find (sometimes only a tooth or finger bone) it not only provides a window into understanding our origins, but our story, which far predates the advent of history. In this sense, looking to the past and digging up fossils, may shed more light on how we understand the notion of human nature and how we should think about it in the future.
Photo: By Author
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