Hand Fossil Turns Back Clock on Complex Tool Use

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The discovery of a 1.4-million-year-old hand-bone fossil reveals that the modern human ability to make and use complex tools may have originated far earlier than scientists previously thought, researchers say.

Turns out evolution isn't always slow.
DCI

A critical trait that distinguishes modern humans from all other species alive today is the ability to make complex tools. It's not just the extraordinarily powerful human brain, but also the human hand, that gives humans this unique ability. In contrast, apes — humans' closest living relatives — lack a powerful and precise enough grip to create and use complex tools effectively.

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A key anatomical feature of the modern human hand is the third metacarpal, a bone in the palm that connects the middle finger to the wrist.

"There's a little projection of bone in the third metacarpal known as a "styloid process" that we need for tools," said study lead author Carol Ward, an anatomist and paleoanthropologist at the University of Missouri."This tiny bit of bone in the palm of the hand helps the metacarpal lock into the wrist, helping the thumb and fingers apply greater amounts of pressure to the wrist and palm. It's part of a whole complex of features that allows us the dexterity and strength to make and use complex tools." (In Images: The Oddities of Human Anatomy)

Until now, this styloid process was found only in modern humans, Neanderthals and other archaic humans. Scientists were unsure when this bone first appeared during the course of human evolution. (The human lineage, the genus Homo, first evolved about 2.5 million years ago in Africa.)

"We had thought the modern human hand was something relatively recent, maybe something that appeared as a recent addition near the origin of our species," Ward told LiveScience.

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Now, researchers have discovered a fossil almost 1.5 million years old that possesses this vital anatomical feature, meaning it existed more than 500,000 years earlier than it was previously known to have existed.

"This suggests this feature might be fundamental to the origin of the genus Homo," Ward said.

The scientists discovered a third metacarpal bone in northern Kenya, west of Lake Turkana. The fossil was found near the sites where the earliest Acheulean tools — named for St. Acheul in France where tools from this culture were first discovered in 1847 — were unearthed. The Acheulean artifacts were the first known complex stone tools, rough hand axes and cleavers that first appeared some 1.8 million years ago.