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Jan. 23, 2014 Volume 35, No. 16

Hominid bone indicates that human hand evolution mostly complete by 1.42 million years ago

Discovery in northern Kenya helps explain proliferation of toolmaking by Homo erectus

Carol Ward

Professor Carol Ward holds a cast of the ancient hand bone. Photo by Rob Hill.

A bump on an ancient hand bone might not sound like a mountain of information. 

But this particular feature on a 1.42 million-year-old metacarpal discovered in 2011 in Kenya has changed the time scale for scientists on the development of the human hand and how it influenced the dawn of hominid technology.

Along with language, bipedalism and advanced tool making are defining traits of modern humans. Charting when the abilities manifested in the hominid lineage is a preoccupation of scientists. In recent years, Carol Ward, MU professor of pathology and anatomical sciences, has helped answer some of the questions.

In 2011, she was on a team of international researchers who analyzed a 3.2 million-year-old foot bone from Ethiopia; the work added to the evidence that Australopithecus afarenis walked upright. In December, Ward and colleagues published in the National Academy of Sciences journal evidence that Homo erectus, by 1.42 million years ago, had hands as developed as those of modern humans. The discovery helps explain the ability of the creatures to make and use stone tools.

The ancient hand bone suggests “an increased dexterity that allowed early human species to use powerful yet precise grips when manipulating objects,” Ward said. “With this discovery, we are closing the gap on the evolutionary history of the human hand.”

Before the find, most scientists believed that the modern hand was not fully developed until 800,000 years ago.

The projection of bone on the base of the third metacarpal of the hand is called the styloid process. It helps the hand lock into the wrist bones, similar to how a ball catch can lock two plastic pipes together. The adaptation greatly increased grip strength and function of the thumb and fingers, enabling Homo erectus to create complex tools. 

“Toolmaking was critical to the survival of these animals,” Ward said.

The West Turkana Paleo Project team made the discovery three years ago on desert scrubland near Lake Turkana, part of the Great Rift Valley in northern Kenya. The valley was created by the separation of two tectonic plates, which resulted in millions of years of sediments, sprinkled with hominid and other animal fossils, being pushed to the surface.

On the west side of Lake Turkana, many game-changing fossils have been found, including complete skulls of new species of early hominids Australopithecus aethiopicus and Kenyanthropus platyops, and even a 1.6 million-year-old Homo erectus skeleton called the Turkana Boy. 

The team minus Ward, who was teaching in Columbia, discovered the hand bone eroding out of the earth in this area. A cast of it was sent to Ward in April 2011. 

Ward spent two years studying and comparing it to bones of today’s primates and other primate fossils.

Scientists dated the fossil by knowing that the area from which it was recovered is of a certain geologic time, achieved in part by carbon dating volcanic ash between recovered bones.

Scientists say Homo erectus had larger jaws than modern humans and a short forehead. The creatures probably had brown skin and were mostly hairless. “You would recognize them as humanlike,” Ward said.

Back then, northern Kenya was mostly grasslands with spotty forests. The creatures lived in groups, and their bipedal travels would have worn paths around Turkana Lake, along the rivers and across the savannah. And, as Ward’s work sugests, they had nimble hands to craft stone tools and, perhaps, baskets and pouches now lost to time.

For a story on MU's anthropology department, click here.