Human aerial bombardments might have pushed Neanderthals to extinction, suggests new research. Changes in bone shape left by a life of overhand throwing hint that Stone Age humans regularly threw heavy objects, such as stones or spears, while Neanderthals did not. "The anatomically modern humans would have this more effective and efficient form of hunting," says Jill Rhodes, a biological anthropologist at Bryn Mawr College in Pennsylvania, who led the new study. A warmer Europe would have opened up forests, enabling longer range hunting, she says.
     Rhodes and a colleague studied changes to the arm bone that connects the shoulder to the elbow – the humerus – to determine when humans may have begun using projectile weapons. "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 says.
     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, Rhodes says. To find out, she and Churchill measured humerus bones from Neanderthals and ancient and modern humans.
     They found some evidence for projectile use in male European humans from around 26,000 to 28,000 years ago – the middle Palaeolithic period – who would have been contemporaries of Neanderthals. Their right humerus bones were generally more rotated toward their back than their left, while Rhodes's team noticed no such asymmetry in Neanderthal arms. "These upper Palaeolithic men were doing something different with their arms than the Neanderthals were," she says.
     The earliest concrete evidence of projectile use comes from a 20,000-year-old spear-throwing device, says Steve Churchill, at Duke University in Durham North Carolina, who co-authored the paper. But as far back as 100,000 years  sharpened stones began to resemble the pointed stone heads of later throwing spears and arrows. This has led some researchers to speculate that the use of projectile weapons originated in Africa – not later on in Europe or other places of human settlement. "It's all very suggestive, but there's no smoking gun there," Churchill says.
     However, Erik Trinkaus, a paleoanthropologist at Washington University in St. Louis, doubts that projectile weapons played a major role in human culture before about 25,000 years ago and the extinction of Neanderthals. "The shift in hunting strategies, there's probably something there, but it's not as pronounced as people make it out to be," he says. Humans may have been hurling aerodynamic stones around the time Neanderthals died out, but spear-throwing did not become a common hunting practice until aeons later, he argues.

Source: NewScientist (20 November 2008)