**Background:** Curiosity—the drive to seek information and reduce uncertainty—is a hallmark of human cognition, but its evolutionary origins and whether it is shared with non-human great apes remain poorly understood. The authors define curiosity as exploration aimed at reducing uncertainty, regardless of underlying motivation or future benefits. They note that prior work has shown orangutans exhibit low curiosity toward novel items unless they observe trusted individuals interacting with them first, while children are known to explore uncertain options even at the cost of immediate rewards. This study directly compares great apes and children in analogous experimental paradigms to assess species differences in uncertainty-driven exploration.
**Methods:** Five studies were conducted. Study 1 tested 29 great apes (15 chimpanzees, 3 gorillas, 6 bonobos, 5 orangutans) in a three-phase paradigm: a pre-test phase where apes learned a color-reward association (e.g., red cup always baited with one grape), a priming phase where they experienced either positive (three grapes) or negative (empty) new colored cups, and a test phase where they chose between the previously positive cup (PPC) and a new colored cup. Only 8 apes advanced past the pre-test phase. Studies 2 and 3 tested apes (Study 2: 15 apes; Study 3: 21 apes) with a simpler paradigm: participants chose between a transparent cup containing one reward and an opaque cup containing three (Study 2) or two (Study 3) unknown rewards. After an intervention phase where the opaque cup's contents were revealed, apes were retested. Study 3 used cups differing in color, material, and shape, and included all apes regardless of initial preferences. Studies 4 and 5 tested children (Study 4: 72 children aged 3–5; Study 5: 52 children aged 3 and 5) with the same basic paradigm using stickers as rewards. Study 4 explicitly told children the goal was to find stickers; Study 5 minimized instructions to match the ape studies more closely. Statistical analyses used Generalized Linear Mixed Models (GLMMs) and non-parametric tests.
**Key Results:** In Study 1, apes who experienced positive priming were more likely to choose the new ambiguous option over the PPC (GLMM: χ²₁ = 10.77, p = 0.001, N = 192), but also performed worse on control trials, suggesting overgeneralization. In Study 2, 11 of 15 apes always chose the transparent cup in phase 1 (Binomial test, p = 0.06), but significantly shifted to the opaque cup in phase 3 (Wilcoxon, p < 0.01; average opaque choice in phase 3 = 86%). In Study 3, 16 of 21 apes chose only the transparent cup in phase 1 (Binomial test, p = 0.015), with a significant shift to the opaque cup in phase 3 (Wilcoxon, p < 0.001; average opaque choice: phase 1 = 16%, phase 3 = 68%). The GLMM confirmed a significant phase effect (χ²₁ = 11.49, p = 0.001, N = 672) but no species differences among apes (χ²₂ = 2.57, p = 0.28). In Study 4, 61 of 72 children chose the opaque cup at least once in phase 1 (Binomial test, p < 0.001; average opaque choice: phase 1 = 52%, phase 3 = 77%). The GLMM showed a significant phase effect (χ²₁ = 7.43, p = 0.006, N = 574) and a non-significant trend for age (χ²₂ = 4.5, p = 0.1). In Study 5, 40 of 52 children chose the opaque cup at least once in phase 1 (Binomial test, p < 0.001; average opaque choice: phase 1 = 41%, phase 3 = 56%). The GLMM was significant (χ²₃ = 6.07, p = 0.048, N = 415) with a significant phase effect (χ²₁ = 4.42, p = 0.035). The direct comparison of Studies 3 and 5 revealed a significant species-by-phase interaction (GLMM: χ²₁ = 8.72, p = 0.003, N = 1087): children were more likely to explore the opaque option in the pre-test phase, while apes mostly chose it after the intervention.
**Clinical Implications:** While not a clinical study, these findings have implications for understanding the developmental and evolutionary foundations of curiosity and exploration. The results suggest that human children possess a stronger intrinsic motivation to resolve uncertainty compared to our closest living relatives, which may have been a key driver in the evolution of human cumulative culture and adaptability. Understanding these motivational differences can inform educational approaches that leverage children's natural curiosity, and may also provide insights into developmental disorders characterized by reduced exploratory behavior or heightened aversion to uncertainty.