Paleolithic Proteins

Paleoanthropologist April Nowell and team have discovered the oldest identifiable animal protein residues on Stone Age tools – suggesting our Paleolithic ancestors feasted on everything from camel to rhino. Nowell of the University of Victoria, tells us more about the findings and analytical method used to identify the proteins.

How did you come to work onthis project?

I have been working in Jordan since 2000 on a variety of different projects. It’s an interesting place to work because it is situated in what is known as the Levantine corridor (the Levant is modern day Jordan, Israel, Syria and Lebanon) between the African and Eurasian continents. For thousands of years, plants and animals – including hominins (ancient human ancestors) – passed through this corridor, referred to by one of my colleagues as a “Paleolithic bus station.” It’s a great place to ask questions about ancient human migration patterns and about how they survived in an often challenging environment. In the early 1990s, the water table in Azraq began to drop due to climate change, which has meant that sediments of the age we are interested in are now accessible to archaeologists.

What did you discover?

Seventeen stone tools tested positive for either horse, camel, rhinoceros, duck or wild cattle (bovine). And I can now tell you that a specific tool was used to hunt or scavenge or kill a specific animal, for example, “this hand axe was used to butcher a horse”!

Our findings also showed that a surprising range of animals were exploited, from duck to rhinoceros, suggesting that the cognitive abilities, social organization and technical know-how of these hominins were surprisingly sophisticated and human-like. Hunting is cognitively, socially and technologically demanding – hunting a duck is not the same as hunting or scavenging a rhino, but both require a great deal of skill. We think that they organized task groups to collect water and plants and to hunt or scavenge animals as the opportunity arose. The story of human evolution is the story of the generalist – and our findings give us the beginnings of that story.

Now we know that identifiable proteins survive this long, we hope that other scientists will use our technique on tools as old or older than ours to help build a comprehensive picture of what our ancestors were eating and how they survived in a variety of environments.

Tell us more about the protein analysis…

The method we used is called crossover immunoelectrophoresis (CIEP). It is highly sensitive – able to detect 10−8 g of protein in a 5 μl sample – and has been extensively tested in forensic contexts. Like less sensitive methods, such as ELISA, radioimmune assays or Western blots, it’s based on antigen-antibody reactions and demands high-quality antisera. Many of the antisera we use are commercially available, except for rhinoceros, as it is not a common research animal in medicine or forensic study. The rhinoceros antiserum was custom-produced by my colleague Cameron Walker in conjunction with another research facility, using a goat as the host animal. We extracted protein samples from microfractures and fissures along the working edges of stone tools by placing them singly into sterile single-use containers, applying the extraction liquid, and floating the container in an ultrasonic bath for at least 15 minutes.  After the ultrasonic bath, the containers with the artifacts and extraction liquid were set on a mechanical rotator for another fifteen minutes prior to pipetting the extraction liquid into micro-centrifuge tubes for refrigerated storage.  In some instances, variations of this extraction protocol were followed due to the size of the artifacts being tested.

As for selecting the tools, we have excavated about 10,000 stone tools and looked at a large number of them under a microscope. My colleague Daniel Stueber and I chose 50 or so that we thought had clear evidence of being used in the past. Because these artifacts are so old and the procedure is expensive, I then selected six for testing. One came back positive for horse. I then sent a larger sample of 38 tools, which has provided us with 17 positives altogether. Our faunal remains now also include a possible lion...