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

Science News,  Feb 10, 2007  by Bruce Bower

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CHANGING SPACES If Iriki and Stout are right, then our prehistoric ancestors didn't invent stone tools out of evolutionary whole cloth. Instead, groups bound by cultural traditions turned a humble neural inheritance into a unique aptitude for toolmaking and other technological pursuits.

That scenario rings true to linguist Stephen C. Levinson of the Max Planck Institute for Psycholinguistics in Nijmegen, the Netherlands. He and his colleagues study how people perceive their locations and orientations relative to those of external objects and plan routes from one spot to another. This mental faculty, known as spatial cognition, contributes to toolmaking and tool use.

In the Nov. 14, 2006 Proceedings of the National Academy of Sciences, Levinson's group asserts that all people innately consult environmental cues to locate themselves in space and to navigate from point A to point B. However, assumptions built into some cultures and languages transform this innate tendency into a preference for using oneself, rather than one's surroundings, as a spatial reference point, the researchers say.

The researchers emphasize that some languages, including English, tend to describe object locations in terms relative to an observer's viewpoint, such as front, back, right, and left. Other languages generally use terms for absolute directions--north, south, east, and west--or refer to familiar landmarks.

In one experiment, the researchers studied 12 adults and 12 children, ages 8 to 10, who spoke Dutch, a language that, like English, uses mainly relative spatial terms. Another 12 adults and 12 children came from an African hunter-gatherer group that typically uses absolute spatial descriptions.

Each volunteer sat in front of a table and watched an experimenter alongside the table place a token under one of five cups positioned like dots on a die--two on the bottom, one in the middle, and two on top. Participants then moved to the opposite side of the table and to another set of cups and indicated where they thought a second token might be hidden.

In a series of trials, Dutch adults and kids rapidly learned where the tokens were and made few errors if the tokens in the two tests maintained position relative to a participant's viewpoint, such as starting out on the bottom left-hand side and again being bottom left after the volunteer moved to the new viewing position. However, their performance declined sharply if the tokens maintained absolute position, such as being located under the northwestern cup--which started out on the lower left and then was upper right after the participants repositioned.

In contrast, the hunter-gatherers excelled at finding hidden tokens that maintained absolute position and stumbled on the other condition.

The researchers then administered a simpler version of the hidden-token test to 12 German 4-year-olds attending preschool as well as 5 orangutans, 7 gorillas, 7 pygmy chimpanzees, and 11 common chimps. Although German adults tend to use relative spatial terms, both the preschoolers and the apes located tokens more readily and accurately when using environmental cues--either absolute or landmark based.