The scientists compared three groups of chimpanzees: one with a history of long-term stable, social interaction with humans (‘enculturated’); a group raised in a sanctuary setting, with only caretaker contact with humans (‘semi-enculturated’); and another group raised under more austere captive conditions (laboratory chimpanzees).  The experiments looked at how the chimpanzees used rakes in order to retrieve a fruit yoghurt reward.  The overall study examined not only whether the chimpanzees understood the properties of the tool, but also whether they understood the reasons why the tool worked.

The researchers gave the animals access to small rakes with either a rigid wooden head or a flimsy fabric head.  Both enculturated and semi-enculturated chimpanzees correctly chose the rigid rake which enabled them to obtain the reward, indicating that both of these groups understood the physical properties of the two different rakes.

The researchers then presented the same two groups with two identical ‘hybrid’ rakes.  Each rake head had a rigid side made of wood (functional) and another side made of flimsy cloth (non-functional).  The reward was placed in front of the rigid side of one rake, and in front of the flimsy side of the second rake.  The animals who picked the rake with the food reward on the rigid side demonstrated that they understood the causal principles behind the functionality of the rake.

The enculturated chimpanzees successfully selected the functional rake, while the sanctuary chimpanzees chose randomly between the two hybrid tools.  The captive laboratory chimpanzees failed both tests, as demonstrated in previously published work(2).

According to Dr. Sarah Boysen, who led the study, “We think our findings mean that the conditions under which chimpanzees are raised, housed, and maintained have long-term effects on their cognitive development, and offer direct comparisons with early experience, issues of attachment, and preschool education for human infants and children,”

The authors conclude that the differences in performance between the three groups are directly attributable to the significant effect of level of enculturation.  They add that “enculturated chimpanzees may be better at learning within a highly social, interactive context because they have heightened attention to the actions of others.”

1. Furlong EE, Boose KJ, Boysen ST (2007).  Raking it in: the impact of enculturation on chimpanzee tool use.  Animal Cognition DOI 10.1007/s10071-007-0091-6

2. Povinelli DJ (2000).  Folk physics for apes: the chimpanzee’s theory of how the world works.  Oxford University Press, New York.

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