The human hand has evolved to differentiate itself distinctively from that of primates with key anatomical features, but the origin of this change is unknown.

Reported in press release, an international team of scientists has discovered a bone from the hand of a human ancestor that walked the Earth some 1.42 million years ago in East Africa. The bone is the earliest known evidence of a modern human hand and it is believed to come from Homo erectus.

"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. "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 is one of the key elements behind the modern human's thumb, connecting the wrist bone to the hand bone and allowing both to take a large amount of pressure from a grasping thumb and fingers. Ward and her team noted that the lack of this bone provided apes and other primates with a challenge in crafting and using tools, something humans mastered with use of the styloid process.

"The styloid process reflects an increased dexterity that allowed early human species to use powerful yet precise grips when manipulating objects," Ward said. "This was something that their predecessors couldn't do as well due to the lack of this styloid process and its associated anatomy."

The bone was discovered at a site very close to where ancient Acheulian tools were discovered. Such tools include stone hand axes more than 1.6 millions years old. They would have taken a great deal of precision to make, meaning the humans at that time would also be doing other complex tasks with their hands.

"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," Ward said. "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."