Science in the Triangle

Steven Churchill is a professor of Evolutionary Anthropology at Duke University. His focus is on the role of projectile weapons in the evolution of humans. Dr.Churchill gave a talk at Sigma Xi as a part of their Pizza Lunch monthly series.

What is a projectile weapon? It is something that can be thrown far away - more than just a couple of meters - and with sufficient power to seriously injure or kill a large animal. A non-projectile weapon, even if it can be thrown with force to a shorter distance of a couple of meters, requires either ambush hunting or chasing the prey into a corner or a bog where it can be approached and stabbed from a close distance. A projectile weapon allows hunters to hunt out in the open, perhaps just hiding in the tall grass. Thus two types of weaponry target different kinds of prey.

But inventing projectile weapons requires refinement in technical skills of making them, technical skills in throwing them, and changes in anatomy to make projectile weapons effective. And once invented, projectile weapons have novel ecological impacts, including impacts on further cultural evolution of humans.

This is what Dr.Churchill is studying. He is focusing on Europe, the invention of projectile weapons by modern (“Cro-Magnon”) humans and lack of such invention in Neanderthals, how that impacted the ecological relationship between the two species, and how that contributed to Neanderthal extinction as well as extinction (through competitive exclusion, as well as direct competition by killing) of all the large European carnivores except wolves.

In the talk, Dr.Churchill surveyed several different aspects of his research. He is approaching the question from several different angles. One is the study of spear tips in the archaeological record - their shape and size, the weight, the aerodynamics of the shape, etc. all tell something about their use as either close-contact or projectile weapons. Some (rare) spear handles and spear-throwers tell their own stories.

Then there is the fossil record of humans, Neanderthals and other large carnivores that show numbers and geographical distributions, migrations and dates of extinctions.

Next, there are anatomical cues - skeleton is malleable during development and bones in the upper arm develop differently in cultures that use contact weapons versus those that use projectile weapons as the stabbing technique is different from the throwing technique - throwers have different torsion angles in the humerus and also the humerus of one arm gets thicker than that of the other arm - this pattern is found in humans, but not in Neanderthals.

Finally, the general shape of Neanderthals would make them strong stabbers but poor throwers, so even if they tried throwing (perhaps by seeing the spears used that way by modern humans) they would not have been effective hunters with that technique.

Then, there are wounds in the bones of some fossil humans and Neanderthals. By conducting an experiment - throwing spears into pig carcasses at various speeds, powers and distances (yes, throwing done by a machine) and analyzing the effects on bones - Churchill and his students could conclude that the wounds in the fossil bones were indeed the result of projectile weapons thrown from a distance.

The talk was, as is usually the case on these occasions, a quick survey of various studies. I did not read all the papers by him or his competitors, so I cannot write anything from a position of my own expertise. But my feeling is this: Each piece of evidence he showed is weak on its own, but put together they make a strong case. And the strength is not purely additive, i.e., in the sense that more data is stronger than fewer data. The strength comes from consilience. Let me try to explain how that works.

Let’s call his preferred hypothesis ‘Hypothesis A’. One piece of evidence he shows is consistent with Hypothesis A, and weakens (or eliminates) an alternative Hypothesis B, but is also strongly vulnerable to alternative Hypothesis C. Another piece of evidence is consistent with his Hypothesis A, and weakens an alternative Hypothesis C, but is also strongly vulnerable to alternative Hypothesis D. Yet another piece of evidence is consistent with his Hypothesis A, and weakens an alternative Hypothesis D, but is also strongly vulnerable to alternative Hypothesis B. When you look at all of his evidence together, all of it is consistent with Hypothesis A and all alternatives look weak. Thus with all pieces being individually weak, the whole edifice still looks very powerful.

Now, to make clear, Dr.Churchill pointed out several times that the research he focuses on, his Hypothesis A, is not the one and only explanation for the extinction of Neanderthals (and other large predators). He just asserts that it is an important component of the process that led to this result and perhaps a more important component than some other people in the field are ready to admit. Of course, that’s how science works: different people focus on different aspects of a problem, and the strength of each person’s data will determine how the whole picture is built in the end.

This was definitely an interesting talk on a topic I never thought about before. DeLene was also there and wrote her thoughts about the lecture on her blog Wild Muse as well as on the Science In The Triangle blog.