The journal Science reports a study showing that mice given a single gene can develop full colour vision. Mice, like most mammals except primates, are normally colourblind. The implanted gene, which is found in humans, is responsible for making a photopigment, a light-sensitive protein in the photoreceptors of the eye. The researchers from the Howard Hughes Medical Institute validated their findings with cell recording and with behavioural tests, demonstrating pretty conclusively that the mice really can see in colour, being able to make discriminations normal mice cannot, and this is because their photoreceptors are sensitive to long wavelength red light.
Because only a single new gene has this effect, the study is reported as demonstrating that primate colour vision could have evolved very suddenly. However, this angle is perhaps less suprising if we consider that colour vision is phylogenetically ancient – primate colour vision doesn’t represent the first time it has evolved, rather primate colour vision is more of a recovery of the function which is found in many non-mammal species such as reptiles. The structural correspondence of this is that the appropriate apparatus for colour vision is extant in mammals – it is just that non-primate mammals lack the appropriate variety in their photopigments. The study is is another demonstration of the amazing ability of the brain to adapt to and take advantage of whatever sensory input is available to it (related to this, see this article on human tetrachromacy, via Slashdot)