The evolution of human-like hands came before the evolution of what would be considered actual humans, showing up initially in some of the oldest and mostly ape-like members of our family tree, a study suggests.
That in turn suggests those early not-quite-humans could have been the first to make tools, process foods and engage in fairly sophisticated tasks, they add.
That challenges a long-standing notion that Homo habilis, also known as "Handy Man," was the first maker of stone tools, the researchers say in a study published in the journal Science.
"Instead, I think our findings show that the traditional view that stone tool use was something that only members of our own genus Homo were capable of is outdated," says researcher Tracy Kivell, a paleoanthropologist with the University of Kent in England.
The researchers looked at fossilized hand bones, specifically the metacarpal bones of the palm of the hand that control the fingers.
Metacarpal bones have soft, spongy tissues at their ends that are altered over a lifetime of use and can yield evidence of what the hand has been doing.
Modern human metacarpals look different from those of ape hands because we utilize our hands differently, mostly in some sort of activity involving a uniquely human pinching movement like holding a pencil or a coffee cup.
However, an examination of metacarpals from four Australopithecus africanus individuals - not-yet humans from around 3 million years ago -- found that while they were tree-dwellers, their metacarpal bones showed signs of tightly pinching small objects, suggests they may have been among the first makers and users of simple stone tools.
"This study is really interesting because it shows how the [A. africanus] hand was actually used, and that's consistent with stone tool use," says Shannon McPherron of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
Australopithecus africanus displayed a mix of ape and human features, with leg and foot bones suited for walking upright but long arms more appropriate for climbing in trees.
The study suggests A. africanus was already starting to use its hands in a manner different from that of its own ancestors, with the ability to be more dexterous and more precise, say experts who've found the similarities between the hand bones of A. africanus and humans compelling.
"The best explanation is that the difference reflects some powerful thumb-to-finger gripping," says John Hawks of the University of Wisconsin-Madison.
If so, the researchers say, it's evidence our early ancestors may have been utilizing tools a half-million years earlier than previously thought.
