The oldest stone tools date back to 2.6 million years ago, and Homo habilis (one of the earliest members of Homo) has long been considered to be the first toolmaker. Their name even means “handy man.” But now, researchers studying fossil hand bones found in Africa have discovered that our early ancestors had “human-like” hands—capable of precision gripping—as early as 3 million years ago. The findings, published in Science this week, suggest that hominins (that’s us and our ancestors) may have been capable of using stone tools more than half a million years before they were even developed.
Trabeculae are tiny, spongy tissue structures that act like beams or struts in hand bones called metacarpals. These remodel quickly, so spongy bone reflects the actual behavior of individuals during their lifetime. That means trabecular patterns indicate whether ancient hominins (such as the pre-Homo australopiths like Lucy) were using their hands to climb in trees—or if they had evolved a more forceful, precise opposition that allowed them to make and use stone stools. Known as squeeze gripping with an opposable thumb, it's how we’re able to use a hammer or a pencil. An example of human precision grip is pictured to the right, grasping an Australopithecus africanus metacarpal.
Using CT scanners, a team led by Matthew Skinner and Tracy Kivell from the University of Kent examined the trabeculae of hand bones from four Australopithecus africanus individuals who lived around 3 to 2 million years ago. These were compared to those of chimpanzees, other Australopithecus species, Homo neanderthalensis, and recent and early Homo sapiens. The cross-sections of their first metacarpals are pictured below (red represents the highest bone volume to total volume). With their short thumbs, chimpanzees lack the forceful precision gripping found in non-tree-living, stone-tool-making extinct Homo species, such as the Neanderthals. (Though chimps are pretty good at dipping sticks into ant mounds.)
Australopithecus africanus, they found, had a human-like trabecular bone pattern in the metacarpals that are consistent with the forceful opposition of the thumb and fingers during tool use. These hominins—who hadn’t been considered toolmakers before—were at least prepared to handle stone tools. However, we won’t know whether they actually did or not until stone tools are found at Australopithecus sites.
Images: T.L. Kivell (top), T.L. Kivell & M. Skinner (middle), M.M. Skinner et al., Science 2015 (bottom)