Introduction

• In evolutionary psychology textbooks, we often encounter non-human primates and other species being compared to humans.

• Examples might be invoked in some domains but not others.

• For example, Buss (2019) writes: ‘other primates besides humans, such as chimpanzees, baboons, and macaques, also engage in reciprocal helping (de Waal, 1982). Taken together, this evidence suggests a long evolutionary history of altruism.’ (p. 502)

• Exploratory study: how do students perceive similarity across various domains.

Methods

• Two pre-registered studies via a crowdsourcing site (Prolific: n = 466; n = 472) focusing on psychology and biology students.

• Study 1: rated similarity to humans for a baboon, gorilla, bonobo, orangutan, and chimpanzee in the following domains: diet, physical anatomy, brain anatomy, cognition, sexual behaviour, disease, physiology, learning, social behaviour, sex differences, and genetics.

• Ratings on a 0-100 slider. “You will now be asked to rate the similarity of non-human primate species to humans with 0 indicating ‘not at all similar’, and 100 indicating ‘totally similar’ across a series of domains.” Species and domains were represented at random.

• Study 2: same design but evaluations of ant, duck, mouse, dolphin, and chimpanzee

• Both studies balanced for ‘Biology’ and ‘Psychology’, then by Gender and Country.

• Analyses were conducted in R 4.4.2 (R Development Core Team, 2008). Psycho’n’etric analysis using CliquePercolation (Lange, 2021) and NetworkComparisonTest (Van Borkulo et al., 2023).

Results

Study 1

Figure 1: Study 1 : Psychometric network analysis

Network invariance: all p > .2 –> Structure is roughly the same.

Strength invariance:

Gorilla - Orangutan , p = .031

Gorilla - Chimp , p = .073

–> Overall picture is largely the same across all species.

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Differences between psychology and biology.

Network invariance: p = .0009

Strength invariance: p = .609

–> but both have the same two clusters of 3 nodes.

Cluster 1 : Genetics, Physiology, Physical Anatomy

Cluster 2 : Cognition, Learning, Social behaviour

Figure 2: Study 1 : Psychometric network analyses by group

Study 2

Figure 3: Study 2 : Psychometric network analysis

Network invariance: some p < .1; Dolphin - ant, p = .045; Duck - ant , p = .056; Duck - Dolphin, p = .051; Mouse - Duck, p = .075, Mouse - Ant, p = .045

–> None of these survive correction for multiple testing – we can broadly compare… .

Strength invariance: Some of these are different at p = .001 (Mouse vs. Ant; Duck vs. Chimp; Chimp vs. Ant). Strength of edges between nodes could vary between species.

–> All, except for duck, have two communities.

Psychology and biology do not significantly differ:

Network invariance: p = .457

Strength invariance: p = .245

Conclusion

• Across two studies we find a differentiation across domains rather than unitary structure.

• Two clusters of domains: One more biological, one more social.

• Many limitations (e.g., Prolific sample, question framing,…)

Acknowledgments

This work is partially supported by a BA-Leverhulme small research grant to Thomas Pollet and Jeanne Bovet.