The human hand plays a defining role in shaping human industry. The question of what we have been able to do as humans is essentially a question of what our hands have been able to do, what the configuration of bones and muscles in our hands have been able to achieve.
Therefore, studying the evolution of the human hand tells us how we have been able to adapt to and engage with our environment through the course of our evolution, since four to six million years ago (Mya) as hominins, the earliest human ancestors.
The modern human hand has a suite of features that enable distinctive grips like the powerful pinch grip, where objects are held between the pad of the thumb and the pads of other fingers. This is made possible by certain protrusions — like the styloid process — and shapes and angles of bones in the wrist joint, according to Carol Ward, of the Department of Pathology and Anatomical Sciences at the University of Missouri-Columbia.
Palaeontologists have thought these features to be a relatively modern addition, from about 800,000 years ago.
However, a fossil dated from 1.42 Mya unearthed by Dr. Ward and her team at a site in Kenya has been found to possess the styloid process. According to their published results, this is an ‘unambiguous’ sign that the human hand developed modern features 600,000 years earlier than thought.
“What this fossil shows us is that the modern human hand did not appear as a recent addition to human biology, but rather extends all the way back to near the origin of our genus, Homo,” Dr. Ward told this correspondent in an email.
In other words, the find pushes back the timeline for how long humans could have used their hands to manipulate tools similar to the way we do today.
The fossil was found at Kaitio in the West Turkana County in Kenya. Its age was determined using radiometric dating techniques on the volcanic ash layers above and below the fossil. Its age — 1.42 million years ago — places it in the early Pleistocene epoch on the geological timeline.
Specifically, Dr. Ward’s team found that the fossil possessed the third metacarpal styloid process, a projection of bone from the base of the metacarpal (bone of the palm) that interlocks with the wrist bones.
This “distinctively human rearrangement of the wrist”, according to their paper published in the Proceedings of the National Academy of Sciences on December 16, coincides with the emergence of Acheulian technology.
Examples of this technology include the distinctive pear-shaped hand-axes and other bifacial stone tools.
“The development of the Acheulian tells us that hominins were using their hands more frequently for more complex tasks, which selected for the hand,” Dr. Ward told this correspondent in an email.
The discovery also provides a basis to address how the earliest-known stone tools date back to almost 2.58 million years, while evidence of the hands necessary to build them doesn’t appear in the fossil record until almost 1.7 million years later.