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Dexterity and Early Tools

Early stone toolmaking marks an important juncture in evolution. The Oldowan stone tools from Hadar, Ethiopia, are among the oldest known, dating back 2.3 million years. Shown from various angles are (a) two sharp-edged flakes and (b) a hand-held chopper. (After Kimbel et al.) In the thumb diagram, the shaded areas show three muscles in the human thumb that chimpanzees normally lack. (After Susman (1994).)

Credits: From Evolutionary Analysis, by Scott Freeman and Jon C. Herron. 1998 by Scott Freeman and Jon C. Herron. Published by Prentice-Hall, Inc.

Dexterity and Early Tools

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Human Evolution


Dexterity and Early Tools:

A few anthropologists have gotten quite good at what seems a rather odd preoccupation: making stone tools the way our hominid ancestors did. They can find a good rounded stone to be the "core," pick up another, called a "hammerstone," and proceed to knock fine-edged "flakes" that are very sharp and could be used to cut meat and scrape animal bones. These hardy individualists have immersed themselves in stone tool manufacture because the point at which our ancestors began to do this marks a critical juncture in evolution. Animals like the chimp -- and even Darwin's finches -- can use sticks they've found as tools. But even when chimps are given stones and shown how to chip tools from them, what they produce doesn't compare to even the most primitive implements that show up in the hominid record about 2.5 million years ago.

Part of the problem is that chimpanzee hands are not well adapted to such delicate work. Chimp thumbs are much shorter in relation to the rest of their hand than are ours, making a "precision grip" between thumb and forefinger difficult. And recent research using 3-D imaging techniques has shown that a humanlike "power grip" is beyond their capabilities as well. The relative importance of these two grips in early stone tool manufacture and use is an area of active research.

But those tools, known as Oldowan because they were first found in Africa's Olduvai Gorge, also reflect some subtle but important advances in thinking that are beyond the abilities of even the smartest chimps. For example, only human ancestors, not chimps, showed the ability to choose the best fine-grained rocks to use, and to understand where and at what angle to strike the core stone to produce a sharp flake.

The discovery of the tools has raised the still-unanswered question of who these tool-makers were. It would be tempting to say they must be early members of the Homo lineage -- that is, on the road to modern humans -- but there aren't any Homo fossils older than 2.3 million years ago, which is too late to be the fabricators of such tools. Recently, a new species of hominid, named Australopithecus garhi, was discovered in association with fossil animal bones that bear the distinctive marks of stone tools, suggesting another candidate for an early toolmaker. A. garhi dates from 2.5 million years ago, and was a small-skulled creature, indicating that tool use came before any significant expansion in the brain. Indeed, one hypothesis proposes that tool use, and the higher-quality diet that it made possible -- whether marrow from scavenged bones, termites extracted with bone tools, as recent research from South Africa suggests, or tubers obtained with digging sticks -- may have been a necessary condition to allow the evolution of large brains, which require a huge amount of nutrition.

Whenever and among whomever toolmaking arose, it came long after the transition from a tree-based locomotion style to the upright-walking stance that freed the hands, which took place at least 4 million years ago and possibly as far back as 6 million years ago. It took considerable change in the hands and fingers to create the deft manipulative abilities of the Homo species. Major changes show up in the fossil record of the species known as Homo habilis, or "handy man." These individuals had a mobile thumb joint, powerful muscles to bend the fingers, and large fingertips -- all adaptations that may have made possible the making and use of stone tools, and came just as the human brain was expanding and undergoing reorganization.

Once tool manufacture and use became an essential component of the human lifestyle, affecting the amount and quality of food an individual could obtain, tool use may have driven the further evolution of the human hand. Individuals whose hands happened to be better adapted for tool use would tend to be better nourished and to successfully raise more children, who in turn would be likely to inherit their parents' hand morphology.

Thus our ancestors' manipulative abilities increased, until the modern human capacities of grasping and manipulating, which allow us to throw a curve ball or play a symphony, were much as they are today.

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