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Ape Research Index (ARI): Quantifying the effect of previous experience in research tasks on cognitive skills in captive chimpanzees

Note: PLOS is delighted to once again partner with the Einstein Foundation Award for Promoting Quality in Research with applications and nominations for this year’s awards open until April 30th, 2023 at 10:00 pm UTC.  The awards program honors researchers who reflect rigor, reliability, robustness, and transparency in their work. To get a flavor of what the Einstein Foundation is looking for we have asked last year’s finalists to write about their work. Last week we featured Open Science Atlas. Today we hear about the Ape Research Index from Elisa Bandini and Sofia Forss from the University of Zurich. You can watch a video here and/or read more below.

Our closest living relatives, chimpanzees, are the primary comparative models for researchers working on a variety of human evolutionary questions. If you try typing in the keywords ‘chimpanzee’, ‘model’ and ‘human’ into google scholar, you will get 27,200,200 pages of results in less than a second (Rolian & Carvalho, 2018), demonstrating the importance of chimpanzees as models across scientific disciplines. Our research lies at the intersection of various fields, including primatology, archaeology, and cultural evolution. To generate insight into the evolution of human and non-human primate cognition and behaviour, we often extrapolate findings from experimental studies with captive apes (in particular, chimpanzees), using these extant primates also as comparative models for early hominins. Generalizing findings from one or two populations of captive chimpanzees to the whole species, and then using these data as basis for a range of questions on human and non-human primate evolution is common practice in the field. However, it was whilst running some of our studies with captive chimpanzees that we realized that this approach is very problematic, for several reasons.

Firstly, we started noticing that despite our best attempts to match the environmental conditions during testing (one of the important benefits of testing in captivity is being able to control the environment more than when testing wild individuals), we were observing a huge amount of inter-individual variation in performance in the problem-solving tasks we provided to the chimpanzees, both within and across populations. We are not the only ones to have noticed variations in performance in captive chimpanzees, yet these differences are often treated more as ´noise´ in the data, and only reported anecdotally. Although easily ignored, these differences in performance in research tasks most likely provide key information on chimpanzee cognition and may jeopardize the generalizability of studies from certain populations of captive chimpanzees. Whilst the role of the environment, genetics and developmental processes in chimpanzee cognition and behaviour is relatively well-understood, one factor that is rarely taken into account is the effect of previous experience. Yet, how previous experience shapes our own behaviour and cognition is a well-researched area in the field of human psychology. As chimpanzees are so closely related to us, we hypothesize that previous experience also influences chimpanzee performance in research tasks. In particular, we argue that the more experience a chimpanzee has in experiments, the better they will perform in subsequent tasks.

If our hypothesis is found to be true, this would have huge repercussions across disciplines that generalize findings from captive chimpanzee populations to generate hypotheses on both non-human and human primate cognition. The current approach in the field is problematic also because of the centralization of captive chimpanzee research, as the majority of studies with captive chimpanzees are carried-out at a handful of institutions around the world. These zoos and sanctuaries have a long-standing reputation for research and attract a steady stream of funding and researchers to test the chimpanzees they house. This has resulted in some populations of captive chimpanzees building up a lifetime of almost daily testing sessions and a huge body of experience in research tasks. Therefore, if we find that previous experience does have an effect on current chimpanzee cognition and behaviour, then we would have to completely reconsider studies that extrapolate data from these intensively studied chimpanzee populations to the whole species, as they might not be reliable representative of the abilities of the species.

Our project, The Ape Research Index (ARI), will investigate this open question by carrying out a meta-analysis of the existing literature to identify the levels of research experience of chimpanzees currently living at institutions around the globe, and correlate their experience levels with their performance in these tasks. Our second objective will be to identify the groups with the highest levels of experience and the ones with the lowest, and directly test both groups with the same test batteries (with tasks novel to both groups), to examine whether previous experience has an effect on their ability to solve new tasks across cognitive domains. Lastly, we will place all this data into a completely open-access database (ARI), which will allow researchers to check the level of previous experience of different captive chimpanzee populations in order to identify the most appropriate sample for their particular research question. This approach will greatly increase the reliability and robustness of comparative cognition studies.


Dr. Elisa Bandini

Dr. Sofia Forss

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