Human behaviour and cognitive development are affected by previous experience and developmental inputs (1). Whilst this phenomenon is widely documented in the human psychological literature, whether and how previous experience affects the behaviour and cognition of our closest living relatives, great apes, is still largely unknown. This is surprising, since researchers often report individual differences in behaviour and performance among apes during experimental studies. Thus, it is very likely that, similar to the human case, apes that have already participated in research in the past will perform differently when tested with novel cognitive tasks compared to individuals who lack such experience. Despite the crucial implications this scenario would have on research on multiple scientific fields like primatology, evolutionary psychology, and comparative cognition, the current literature largely overlooks the impact of research experience, and findings from captive apes with a wide range of research experience are often generalised on species-wide level. Consequently, cognitive research on apes most likely suffers from false positive and false negative errors, skewing our understanding of their cognition and behaviour (2 & 3).
These potential errors are magnified by the fact that research on apes, and in particular chimpanzees, is highly centralised across a handful of zoological institutions (4). These institutions have a long-standing history of ape research, attracting a continuous stream of both researchers and funding to continue studying the individuals they house. Therefore, there are several populations of captive apes that have been tested repeatedly for over 20 years, creating a subset of individuals that have accumulated a huge amount of experience of cognitive tasks not common to less intensely studied captive groups. This research centralisation results in an over-representation of data from apes that may not be characteristic of the whole species, which poses a critical problem as the findings from these studies are often generalised on a species-wide level, and parallels to human cognitive skills are drawn from a sub-sample of experienced apes. The Ape Research Index (ARI) project proposes to tackle this issue by measuring and quantifying the bias in both the literature and via targeted experiments (see Home tab).
See also: https://award.einsteinfoundation.de/award-winners-finalists/recipients-2022/early-career-award-2022 and https://www.youtube.com/watch?v=F8FW_GZZIro for more information on the project.
References:
Bouchard, T. J., Lykken, D. T., McGue, M., Segal, N. L., & Tellegen, A. (1990). Sources of human psychological differences: The Minnesota study of twins reared apart. Science, 250(4978), 223–228.
Bohn, M., Eckert, J., Hanus, D., Lugauer, B., Holtmann, J., & Haun, D. B. (2023). Great ape cognition is structured by stable cognitive abilities and predicted by developmental conditions. Nature Ecology & Evolution, 7(6), 927-938.
Webster, M. M., & Rutz, C. (2020). How STRANGE are your study animals?. Nature, 582(7812), 337-340.
Langlitz, N. (2020). Chimpanzee culture wars. Princeton University Press: London.