Unique arm morphology in Neandertals was likely caused by scraping activities such as hide preparation, not spear thrusting as previously theorized, according to research published July 18 in the open access journal PLoS ONE.

The researchers, led by Colin Shaw of the University of Cambridge, took muscle measurements of modern men performing three different spear thrusting tasks and four different scraping tasks.

They found that muscle activity was significantly higher on the left side of the body for spear thrusting tasks relative to the right side of the body.

This does not explain the observed Neandertal morphology, though, which shows dominant strength on the right side, casting doubt on the hypothesis that spear thrusting was responsible for the observed asymmetry.

When the study participants performed scraping tasks, however, the activity was much higher on their right side compared to their left, suggesting that scraping behavior may be the actual source of the arm morphology asymmetry and offering interesting insight into Neandertal behavior.

Shaw explains, "The skeletal remains of Neandertals suggests that they were doing something intense or repetitive, or both, that significantly impacted their lives. While hunting was important to Neandertals, our research suggests that much of their time was spent performing other tasks, such as preparing the skins of large animals. If we are right, it changes our picture of the daily activities of Neandertals."

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