Trichromatic Colour Vision: The Choice between Red and Green Colour in Chlorocebus aethiops

Two main theories try to explain the nature of the selective pressure that led to trichromatic colour vision in primates. The foraging hypothesis suggests that colour discrimination is linked to the detection and selection of food, whereas another hypothesis connects trichromacy to the perception of skin colour signaling in a socio-sexual context. The goal of this study was to investigate which hypothesis could be the most plausible to explain the evolution of trichromatic colour vision. At this purpose the colour preference of a colony of vervet monkeys (Chlorocebus aethiops) hosted at Parco Natura Viva – Garda Zoological Park was investigated. Couples of red and green bags containing the same hidden reward were placed in the outdoor enclosure of vervet monkeys and their choice between red and green objects was recorded in order to investigate the effects of colour cues on object preference in the social context. Moreover, the hand used to retrieve objects was recorded to assess a possible relation between hand preference and colour choices. Results indicate that choices do not seem to be based on object colour. However, monkeys showed a significant right-hand preference to retrieve green objects. In conclusion, these observations seem not to support the foraging hypothesis of the origin of colour vision. Therefore, the role of intraspecific socio-sexual communication could be more plausible for the evolution of trichromacy, but this aspect should be better investigate in future studies.