Fair Comparisons Between Children & Apes

The journal of Science in February, 2008, finally published a letter submitted to them mid September, 2007, by Frans BM de Waal, Christophe Boesch, Victoria Horner, and Andrew Whiten, under the heading “Comparing social skills of children and apes” (Science 319: 569). Below, we reproduce the original, which is slightly longer than the published version.

A recent study in Science by Esther Herrmann et al. (7 September 2007, p. 1360) claims equivalence in technical skills between apes – chimpanzees and orangutans – and two-year-old human children, but inferior social skills in the apes. These results are taken as support for a “cultural intelligence hypothesis.”

The study features an impressive battery of tests, seemingly administered in the same format to apes and children. It has been pointed out before, however, that the easiest way to standardize conditions – by having a human experimenter provide the social cues – introduces handicaps for the apes. When the experimenter is human for all subjects, only the apes are dealing with a species other than their own. This may not be as relevant for physical or technical problems, which focus on inanimate objects, but one expects this to matter for social tasks which rely crucially on the relation between experimenter and subject. The reported findings are consistent with the apes being handicapped specifically in the social domain.

The differences between the set ups for children and apes in this study appear multifold. Human children sit on or next to their parent (introducing potential “Clever Hans” effects), are talked to, are used to dealing with human strangers, and are tested by a member of their own species. The apes are alone, observe the task from behind a barrier, receive no verbal instructions, and are tested by a species not their own. We are not suggesting that human experimenters should never be used, but that the social skills which matter most for apes, especially as they relate to culture, are those shown with conspecific models.

Study set-ups for children (above) and chimpanzees (from Hermann et al 2007, online material)

In fact, evidence for ape-to-ape social learning is plentiful. Studies of wild chimpanzees in Africa have documented an impressive array of group-specific traditions attributed to social learning. Apes tested with a human model whom they have grown close to, or with a familiar member of their group, have recently demonstrated social learning that has extended to high-fidelity cultural transmission within and between groups. For the latest studies on this, explore our cultural learning website.

These findings conflict with the results as well as the central thesis of Herrmann et al. Ignoring this literature, as they have chosen to do, can only lead to a fragmented literature, a situation exacerbated by the fact that a “cultural intelligence hypothesis” already exists, formulated to explain the cultural complexity of both humans and the great apes. Mysteriously, given the title of Herrmann et al.’s article, this earlier usage of the term also remains uncited. We strongly urge testing of cognition in ecologically valid settings, such as testing social skills with conspecifics. The problem of the human model would be even more severe in relation to Herrmann et al.’s proposal to extend their test battery to more distantly related species.

As a thought experiment, ask what would happen if we trained apes to apply tests to human children so that these, too, faced a species-barrier. We doubt that this would do the children’s performance any good!

–Victoria Horner

For further reading on the controversy of how to fairly compare apes with children, see the following two publications:

* Chapter 6 of de Waal, F. B. M. 2001. The Ape and the Sushi Master. New York: Basic Books.
* Boesch, C. 2007. What Makes Us Human? The Challenge of Cognitive Cross-Species Comparison. J. Comp. Psychol. 121: 227-240.