Well-tooled primates: the evolutionary roots of our technological prowess may run deep

Science News,  Feb 10, 2007  by Bruce Bower

• E-mail
• Print
• Link

Tool use by monkeys may even promote a behavior that Iriki regards as an evolutionary precursor of language. When monkeys were first trained to rake in food and then to produce cooing sounds to ask for food, they spontaneously began to emit two acoustically distinctive coos--one for food and another requesting a rake to retrieve food. These findings suggest that human ancestors parlayed stone-tool pursuits into advances in speech, using sounds to label various objects, Iriki asserts.

"Their tool use could have contributed to the emergence of perceiving meaning in language and other higher cognitive functions," he suggests.

ROCK SOLID As Stout pored over human-brain data from his novice stone-tool makers last year, Iriki's studies came to mind. The parietal neighborhoods activated in rake-trained monkeys had geared up when Stout used positron-emission tomography to monitor the volunteers' brains' energy use during their toolmaking sessions.

However, stone-tool making ignited brain regions aside from the seemingly ancient network that Iriki observed in macaques, Stout reports in a 2007 Neuropsychologia (vol. 45, issue 5). Toolmaking practice enlivened brain areas that regulate handgrips and that mediate visual attention in people.

An additional parietal area displayed pronounced activity as toolmakers gained skills. Studies directed by neuroscientist Guy A. Orban of K.U. Leuven Medical School in Belgium suggest that this region is present in people, but not in apes or monkeys. It boosts three-dimensional perception and enhances the clarity of moving images--handy attributes for toolmakers.

For Stout, these findings suggest that ancient toolmaking rested on extensive practice that improved people's visual analysis of rocks and the fluidity of the actions needed to produce sharp flakes. Earlier work indicated that novices learned by doing and by getting feedback from experienced workers, not by following rules (SN: 4/12/03, p. 234).

Neuroscientist Scott H. Frey of the University of Oregon in Eugene sees Stout's results as consistent with studies of more-mundane tool use. Using functional magnetic resonance imaging to track blood-flow changes in the brain, Frey's group has found that people who are planning to, say, eat with a spoon or pound with a hammer galvanize a widespread network of regions in the left brain, including frontal and parietal tissue.

When actually using such implements, the same individuals display activity largely relegated to the parietal areas emphasized by Stout. "These regions are involved in transforming sensory information into motor commands," Frey says.

He suspects that expert stone-tool makers also call on a broad network of left brain structures, including frontal areas linked to planning and memory.

Psychologist Arthur Glenberg of the University of Wisconsin-Madison suggests that further research examine whether parietal responses are stimulated by stone-tool making itself or by practicing any set of goal-directed actions.