Daniel Osorio

It is over two centuries since Thomas Young pointedout that the eye is an imperfect measuring instrument,which has to make a compromise between samplingspectral and spatial information. Young was aware thatthe eye is trichromatic, and perhaps in the light of thisknowledge suggested that trichromacy is indeed thebest compromise. Young of course preceded Darwin,and the philosophy and insight underlying his argu-ments were a necessary prelude to Darwinism. At thesame time his conclusion has the flavour of a naïve‘Just so story’, about how we see colour. I will ask howthe different and perhaps competing functions of thephotoreceptor signals in natural behaviour mightexplain the spectral sensitivities of our three conetypes, and also the diversity of colour vision in theprimates of the New World and Madagascar. What ifanything can we add to Young’s understanding of thedesign of our eyes?