Early preference for face-like stimuli in solitary species as revealed by tortoise hatchlings

At the beginning of life, inexperienced babies and human fetuses, domestic chicks, and monkeys exhibit a preference for faces and face-like configurations (three blobs arranged like an upside-down triangle). Because all of these species have parental care, it is not clear whether the early preference for faces is a mechanism for orienting toward the conspecifics and sustaining parental care, or a more general mechanism to attend to living beings. We contrasted these hypotheses by testing inexperienced hatchlings of five species of tortoises, solitary animals with no parental care. If early face-like preference evolved in the context of parental care, solitary species should not exhibit it. We observed that visually naïve tortoises prefer to approach face-like patterns over alternative configurations. The predisposition to approach face-like stimuli observed in hatchlings of these solitary species suggests the presence of an ancient mechanism, ancestral to the evolution of reptiles and mammals, that sustains the exploratory responses, and potentially learning, in both solitary and social species.