Though humans are far from the only animals who are capable of using tools, we can use them more efficiently than any other species on the planet. This ability is not just due to our highly evolved brains, but also because of the unique morphology of our hands. There used to be a fairly large gap in our evolutionary history about where certain features of our tool-friendly hands came from, but the discovery of a 1.42 million year old hand bone has bridged that gap. The results come from lead author Carol Ward from the University of Missouri and were published in the Proceedings of the National Academy of Sciences.
A 1.42 million-year-old metacarpal bone was discovered at a fossil site in Kenya. It was attributed to the early human species Homo erectus, and has a very important feature: a styloid process. The styloid process is a small bony bump at the proximal end of the bone, and can be found on several bones in the body. In the hand, it connects the hand to the wrist and allows much more pressure to be applied to a closed hand while gripping an object, like when swinging a hammer. This is critical to the ability to make and use tools much more effectively. The emergence of the styloid process may have also been easier on the wrist joint, which could have staved off the onset of arthritis.
This discovery is very significant because it pushes back the evolution of this bony landmark back by about 600,000 years. It has been seen in relatively recent human species like Neanderthals, but it hasn’t been clear where the trait emerged. Now, it appears that Homo erectus may be the earliest common ancestor with a styloid process.
The fossil site where the metacarpal was discovered also had many stone tools in the area, reaching as far back as 1.6 million years ago. Some of these tools included axes and hammers. The earliest evidence of stone tool use is around 3.4 million years old. As there were many different hominin groups living at the time of Homo erectus, those individuals with a styloid process likely had a very large advantage over those that did not.