Fossil Hand Closes Gap Evolutionary Record
December 17, 2013

1.4 Million Year-old Fossil Lends A Hand In Closing Evolutionary Gap

Bryan P. Carpender for - Your Universe Online

It turns out that humans might have been working their fingers to the bone much earlier than scientists previously thought – half a million years earlier, according to a new study published this week. The recent discovery of a 1.4 million year-old fossil at a dig site in West Turkana, Kenya could be the key to closing a significant gap that exists in the evolutionary record of humans.

One characteristic that separates humans from apes and other non-human primates is a distinctive hand anatomy that allows them to both make tools and utilize them. The point in time at which these anatomical features first appeared in the span of human evolution has been unknown. However, this new discovery could provide clues that could help determine that time.

An international team of researchers has found a new hand bone from a human ancestor who existed approximately 1.42 million years ago. Scientists believe that the newly discovered bone belonged to the early human species, Homo erectus.

The discovery of this bone is the earliest evidence of a modern human-like hand. In fact, this new discovery suggests that this anatomical feature existed more than half a million years earlier than scientists had previously estimated.

"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 Carol Ward, professor of pathology and anatomical sciences at the University of Missouri, Columbia. "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."

What makes this discovery so important is that the styloid process helps the hand bone lock into the wrist bones, thereby allowing for greater amounts of pressure to be applied to the wrist and hand from a grasping thumb and fingers. This would enable the ability to make and use tools.

It was this lack of styloid process that created challenges for apes and earlier humans who attempted to make and use tools. Further, the lack of a styloid process may have increased the chances of developing arthritis earlier.

A West Turkana Paleo Project team, led by Ward’s colleague and co-author Fredrick Manthi of the National Museums of Kenya, made the discovery. The bone was found near archaeological sites where the earliest Acheulian tools are known to have appeared.

These shaped stone tools include some stone hand axes dated at more than 1.6 millions years old. The existence of such tools and the ability to craft them provides further evidence that early humans were almost certainly performing other complex tasks, all of which would have required a higher level of dexterity.

"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," Ward said.

"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."

With these new discoveries turning back the clock on this vital anatomical feature by more than 500,000 years, Ward and her fellow researchers now want to find older hand bones to better determine when this transition to modern hand anatomy took place.

Ward’s team who helped discover and analyze the bone include: Matthew Tocheri, National Museum of Natural History in the Smithsonian Institution; J. Michael Plavcan, University of Arkansas; Francis Brown, University of Utah; and Fredrick Manthi, National Museums of Kenya. Their study was published in the Proceedings of the National Academy of Science this week.