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Discovery of 1.4 Million-Year-Old Fossil Human Hand Bone Closes Evolution Gap

Christian Basi, University of Missouri

Early humans may have developed the hand anatomy to make and use tools more than half a million years earlier than previously believed.

Researchers found the earliest evidence of a modern human-like hand with the discovery of a hand bone from a human ancestor who roamed the earth in East Africa approximately 1.42 million years ago. They suspect it belonged to the early human species, Homo erectus.

The styloid process is a projection of bone. Ward and her team found a styloid process at the end of a wrist bone more than 1.42 million years old, indicating this anatomical feature existed more than half a million years earlier than previously known. (Credit: University of Missouri)

The styloid process is a projection of bone. Ward and her team found a styloid process at the end of a wrist bone more than 1.42 million years old, indicating this anatomical feature existed more than half a million years earlier than previously known. (Credit: University of Missouri)

Humans have a distinctive hand anatomy that apes and other nonhuman primates don’t have, and the point in time at which these features first appeared in human evolution has been unknown.

“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,” says Carol Ward, professor of pathology and anatomical sciences at the University of Missouri.

“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, Neandertals, 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. Also, 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. 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, Ward says.

HAND 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 says.

“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.”

The study was published in the Proceedings of the National Academy of SciencesResearchers from the University of Arkansas, the University of Utah, the National Museum of Natural History in the Smithsonian Institution, and National Museums of Kenya contributed to the research.

Source: University of Missouri

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