Gibbons (Nomascus leucogenys), siamangs (Symphalangus syndactylus), and chimpanzees (Pan troglodytes) account for proportional probabilities in a two-choice task.

Probabilistic reasoning-the ability to predict outcomes based on the likelihood of different possibilities-is a key component of numerical cognition and is critical for navigating uncertain environments. However, it is unclear whether this capacity i…

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