Ancient Human Ancestor Evolved Agile Hands Earlier Than Thought

Part of why humans are so successful as a species is their hands. In fact, it's our distinctive hand anatomy that allows us to make and use tools in a certain way. While apes and other nonhuman primates also have hands, they don't have the unique anatomical features that humans possess. Now, scientists have uncovered a bit more about human hand evolution; they've found a new hand bone from a human ancestor who roamed East Africa about 1.42 million years ago, revealing that this hand evolution occurred far earlier than expected.

The new hand bone was found near sites where the earliest Acheulian tools have appeared. These tools are ancient, shaped stone tools that include stone hand axes that are more than 1.6 million years old. The ability to make such tools indicates that the early humans at these sites were probably capable of other complex tasks.

"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 one of the researchers, in a news release. "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. This allows for greater amounts of pressure to be applied to the wrist and hand from a grasping thumb and fingers. In apes, the lack of the styloid process presents a challenge when they try to make and use tools. In addition, this lack of a styloid process could increase the chances of having arthritis earlier.

"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," said Ward in a news release. "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."

The findings are important for better understanding how the human hand emerged over the course of evolution. More specifically, it shows how this ancient ancestor was able to use tools due to its distinct hand anatomy.

The findings are published in the journal Proceedings of the National Academy of Sciences.