SEXUAL arousal is often signalled by the colour red. Human faces flush and chimp’s rumps turn red. Now researchers have suggested that colour vision in primates – the only mammals with the ability – may have evolved to pick up on these emotional cues.
Mark Changizi and colleagues at the California Institute of Technology in Pasadena looked at how the colour of haemoglobin, the molecule in the blood that transports oxygen, varied with or without oxygen. Oxygenated haemoglobin appears red, and makes skin above it appear red too. The deoxygenated form makes skin appear greenish blue.
Changizi and colleagues analysed data on…
