New Scientist reports on Carol Ward’s presentation at the AAPA meetings, describing a new metacarpal of Homo erectus from West Turkana: “Stone tools helped shape human hands”. It is a third metacarpal, a bone that happens to be pretty different between known australopithecines and recent Homo. But strikingly none have yet been described for Homo before the Neandertals.
Because the fossil is younger than the first tools, Ward's team believe it is the first evidence of anatomy evolving to suit a new technology. As stone tools became more widespread, those who had the wrist structure to use them would have had an evolutionary advantage over their weaker-wristed kin. "The way we look today has been shaped by our behaviour over millions of years," says Ward.
The developmental change represented by this anatomy is a separate center of ossification at the base of the metacarpal leading to a pointy projection called the styloid process. That’s a pretty interesting shift in development, and so I’m intrigued that it came closely after the appearance of Homo erectus. Ward also reported that the bone is very long, at the top end of the variation in living people and longer than any Neandertals. Another hint of big people in the Early Pleistocene of East Africa.