Chimps Gain Smarts From Hanging With Humans

Charles Q. Choi, MSNBC, June 19, 2007

A bit of human nature can apparently rub off on chimpanzees. Chimps nurtured by humans since birth have a far better chance of figuring out how to use new tools, a new study shows.

The findings highlight untapped potential within chimpanzees that can get uncovered “by studying them when they have been raised under very comparable conditions as our own children,” said Ohio State University cognitive primatologist Sally Boysen.

The research suggests that early human ancestors may have been far more sophisticated in their mental capacities than previously thought, she added.

“The emergence of higher order thinking, as well as motor skills that would permit complex tool use and construction and other cultural features of human social interaction, may have been part of our human ancestry much earlier than otherwise predicted by the fossil record of artifacts and human remains,” Boysen told LiveScience.

The rake test

Boysen and her colleagues compared three groups of chimps. The first group of nine, dubbed “enculturated,” had a long history of socializing with humans. The next group of six dwelt in a chimpanzee sanctuary, with only caretakers as their contact with humans. The last group of seven was raised in more austere lab conditions.

The scientists next showed chimpanzees how they could use small rakes to retrieve a fruit yogurt reward. The rakes either had a rigid plywood head or a flimsy cloth head. The enculturated and sanctuary chimps all correctly picked the rigid rake to help them get the reward, save one enculturated juvenile male, Keeli, who preferred destroying the flimsy rake to getting the reward.


Lab chimps fail

Boysen and her colleagues then presented the chimpanzees with two identical “hybrid” rakes. The heads of each of these rakes had a side made of plywood and a side made of cloth. The yogurt reward was placed before the rigid side of one rake and in front of the flimsy side of the other rake.

The enculturated chimps successfully chose the hybrid rake that would get them yogurt, as seen in the researchers’ video, while the sanctuary apes randomly chose between the tools, findings detailed online in the journal Animal Cognition. This suggests the more chimps had socialized with humans beforehand, the better they were at understanding the actual reason why each tool worked or did not work.

The lab chimpanzees failed both tests given the other chimps. “Since we were able to measure significant differences in nonhumans, imagine the exponential impact on human children under difficult and impoverished conditions in the home that can have long-term effects on their ability to pay attention, remember, learn and process information in general,” Boysen said.


‘Enculturation’ has limits

Boysen and her colleagues suggest chimpanzees nurtured by humans are better at paying attention to the actions of others.


The findings also highlight the need “for a stimulating and enriched environment for captive apes in all settings, including zoos, but more importantly laboratory environments where the negative effects of early rearing, housing and daily care can affect the scientific validity of research, animal health and indeed, quality and length of their lives in captivity,” Boysen added.

[Editor’s Note: “Raking it in: the impact of enculturation on chimpanzee tool use,” by E. E. Furlong1, K. J. Boose1 and S. T. Boysen can be read in PDF or HTML format here. There is a charge.]

Abstract: Raking It In: The Impact Of Enculturation On Chimpanzee Tool Use

E. E. Furlong1, K. J. Boose1 and S. T. Boysen (1)

(1) Department of Psychology, The Ohio State University, 209 Psychology Building, 1835 Neil Ave., Columbus, OH 43210-1222, USA

Received: 16 June 2005 Revised: 19 November 2006 Accepted: 11 April 2007 Published online: 22 May 2007

Abstract Recent evidence for different tool kits, proposed to be based upon culture-like transmission, have been observed across different chimpanzee communities across Western Africa. In light of these findings, the reported failures by seven captive juvenile chimpanzees tested with 27 tool use tasks (Povinelli 2000) seem enigmatic. Here we report successful performance by a group of nine captive, enculturated chimpanzees, and limited success by a group of six semi-enculturated chimpanzees, on two of the Povinelli tasks, the Flimsy Tool task, and the Hybrid Tool task. All chimpanzees were presented with a rake with a flimsy head and a second rake with a rigid head, either of which could be used to attempt to retrieve a food reward that was out of reach. The rigid rake was constructed such that it had the necessary functional features to permit successful retrieval, while the flimsy rake did not. Both chimpanzee groups in the present experiment selected the functional rigid tool correctly to use during the Flimsy Tool task. All animals were then presented with two “hybrid rakes” A and B, with one half of each rake head constructed from flimsy, non-functional fabric, and the other half of the head was made of wood. Food rewards were placed in front of the rigid side of Rake A and the flimsy side of Rake B. To be successful, the chimps needed to choose the rake that had the reward in front of the rigid side of the rake head. The fully enculturated animals were successful in selecting the functional rake, while the semi-enculturated subjects chose randomly between the two hybrid tools. Compared with findings from Povinelli, whose non-enculturated animals failed both tasks, our results demonstrate that chimpanzees reared under conditions of semi-enculturation could learn to discriminate correctly the necessary tool through trial-and-error during the Flimsy Tool task, but were unable to recognize the functional relationship necessary for retrieving the reward with the “hybrid” rake. In contrast, the enculturated chimpanzees were correct in their choices during both the Flimsy Tool and the Hybrid Tool tasks. These results provide the first empirical evidence for the differential effects of enculturation on subsequent tool use capacities in captive chimpanzees.

Keywords Tool use—Enculturation—Social learning—Chimpanzees


S. T. Boysen

Email: [email protected]


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