Somedays, it’s just awful to have the mind of a 12 year old boy. So I’m reading this serious and interesting paper on Neandertals, and learn something new.
Two particular characteristics have received considerable attention; pronounced humeral diaphysis strength asymmetry and anteroposteriorly strengthened humeral diaphyseal shape. In particular, humeral bilateral asymmetry for cross-sectional area, and torsional and average bending rigidity, appear exceptionally high in Neandertals (averaging 24–57%) compared to skeletal samples of modern Holocene H. sapiens (averaging 5–14%).
That’s science-speak for “Neandertals had massively muscular right arms compared to their left.” And my mind went right into the gutter.
Anthropologists had their own less juvenile explanations: their strong right arms were a response to extreme muscular activity of repetitive thrusting (ack, back into the gutter) with long, heavy spears (slap me hard.) The paper, though, analyzed muscular activity in experimental subjects who made spear thrusts while hooked up to loads of instrumentation, and discovered that, contrary to their expectations, it was the left arm, the off hand, that carried the largest load in stabilizing the thrust. So that hypothesis simply doesn’t work.
So they tested an alternative explanation, and it wasn’t the first one that leapt to my mind. One of the most common kinds of tools found at Neandertal sites are scrapers —if you’re using hides for clothing and shelter, there is a lot of processing involved — prolonged, repetitive scraping motions while stripping excess flesh from the underside of skins. I imagine scraping a mammoth skin is a huge endeavor that does involve a lot of work. They reviewed ethnographic studies, and discovered that processing a single cow hide, for instance, takes 6-10 hours of work. So they hooked up their test subjects to instruments and measured muscle activity during scraping…and it matches, generating forces that could lead to a build-up of muscle and bone in the right arm.
Unfortunately for my adolescent Neandertal wanking hypothesis, though, the comparison probably doesn’t hold up. Even the most obsessive individual is going to be hard up to maintain 6-10 hours of constant activity. Rats, I guess I’m not going to be making a novel contribution to anthropology. Besides, I imagine this guess was made many times before, and for some reason never made it into print.
Shaw CN, Hofmann CL, Petraglia MD, Stock JT, Gottschall JS (2012) Neandertal Humeri May Reflect Adaptation to Scraping Tasks, but Not Spear Thrusting. PLoS ONE 7(7): e40349. doi:10.1371/journal.pone.0040349.