A tiny bone of an early human species, possibly Homo erectus, found in Kenya is the earliest evidence of a modern human-like hand, according to a team of scientists led by Prof Carol Ward from the University of Missouri.
This is an artist’s reconstruction of Homo erectus. Image credit: Yale University.
Modern humans have a distinctive hand anatomy that allows them to make and use tools. Apes and other primates do not have these anatomical features in their hands, and the point in time at which these features first appeared in human evolution is unknown.
The newly discovered fossil bone of Homo indicates that this feature existed more than 600,000 years earlier than previously documented.
“This bone is the third metacarpal in the hand, which connects to the middle finger. It was discovered at the Kaitio site in West Turkana, Kenya,” said Prof Ward, who reported the discovery in the Proceedings of the National Academy of Sciences.
“What makes this bone so distinct is that the presence of a styloid process, or projection of bone, at the end that connects to the wrist. Until now, this styloid process has been found only in us, Neanderthals and other archaic humans.”
The styloid process helps the hand bone lock into the wrist bones, allowing for greater amounts of pressure to be applied to the wrist and hand from a grasping thumb and fingers.
“A lack of the styloid process created challenges for apes and earlier humans when they attempted to make and use tools. This lack of a styloid process may have increased the chances of having arthritis earlier.”
The bone was found near sites where the earliest Acheulian tools have appeared. Acheulian tools are ancient, shaped stone tools that include stone hand axes more than 1.6 million years old.
This is a 1.4-million-year-old hand bone of an early Homo found at the Kaitio site in West Turkana, Kenya. Image credit: University of Missouri.
“Being able to make such precise tools indicates that these early humans were almost certainly using their hands for many other complex tasks as well,” Prof Ward said.
“The styloid process reflects an increased dexterity that allowed early human species to use powerful yet precise grips when manipulating objects. This was something that their predecessors couldn’t do as well due to the lack of this styloid process and its associated anatomy.”
“With this discovery, we are closing the gap on the evolutionary history of the human hand. This may not be the first appearance of the modern human hand, but we believe that it is close to the origin, given that we do not see this anatomy in any human fossils older than 1.8 million years.”
“Our specialized, dexterous hands have been with us for most of the evolutionary history of our genus, Homo. They are – and have been for almost 1.5 million years – fundamental to our survival,” Prof Ward concluded.
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Ward CV et al. Early Pleistocene third metacarpal from Kenya and the evolution of modern human-like hand morphology. PNAS, published online December 16, 2013; doi: 10.1073/pnas.1316014110
