"If we're trying to understand whether anatomically modern humans had projectiles, then why not read the signature that it can imprint in the skeleton," Rhodes said.
Studies of elite handball and baseball players suggest that frequent overhand throwing from an early age permanently rotates the shoulder-end of the humerus toward an athlete's back, compared to people who haven't spent much time hurling.
This bone rotation only occurs in the throwing arm, so a difference between the right and left arm in fossils could be a sign of projectile use, according to Rhodes.
I would posit that pitchers are probably not the best model for this sort of analysis. They throw 90-mile an hour fastballs at a frequency (and speed) that far outstrips that of your average hunter-gatherer. Why not go after actual hunters and gatherers to see what sort of adaptations are present there? Further, there might be other factors that contribute to the anatomical discrepancies. Time to go read the article.