Colour

Just as a writer plays with words, a painter works with colours. Good painters dance back and forth across an infinite splendour of hues. For novice like me, it may require a hell of a lot of lessons to learn the know-how.

Yes, though it shames me to say it now, I wasn't sure what to answer when my wife quizzed me about the three primary colours. Truth be told, I've been having a hard time figuring out the colours of the clothes in my wardrobe. Wearing a black suit and charcoal grey trousers is the closest I will ever come to colour matching.

It's one thing for my wife to understand my difficulty with colours, but quite another for the genetic logic to explain the evolution of colour vision in primates and other vertebrates. Colour (like beauty), I was taught, is in the brain of the beholder. In other words, the colours are not "out there," but are constructed in our brain from sensory inputs. Quiz a dog, for example, the primary colour and he will answer you blue and red. Dogs have only two types of specialized receptor cells called cones, with peaks of sensitivity in blue and red. And yes, the majority of mammals have two-colour vision while most birds, reptiles, and even goldfish have four cone types, giving them four-colour vision.

Having less colour vision among mammals, obviously, is at odds with our intuition (and ego). To help us understand the difference, we have to take a time machine and travel to Mesozoic, the age of the reptiles, when mammals were still small, insectivorous shrew-like nocturnal creatures. In the wee hours, early mammals would have depended upon rods (light-receptors in very dim light) rather than cones. Two-colour vision suffices and, in fact, could have been a great plus. Subjects with two-colour vision have been shown to be better in spotting patterns that were camouflaged by colour.

However, diurnal mammals evolved after the demise of the dinosaurs. And these diurnal primates switched to fruit-eating. The mammalian two-colour vision system was never good enough for seeing red fruits against a background of green leaves. This adaptation to diurnal foraging for fruits is probably the secret for evolution to our current three-colour vision.

Ah, you may ask, how on earth would red-green colour blindness be that common in men? That has something to do with the location of the gene coding for the protein that detects visible light in the red spectrum. It so happens that this gene is situated on the X chromosome. In primates and other mammals, X is a sex chromosome that is present as two copies in females, but only as one copy in males. With two copies of the X chromosome, females could have the upper hand in discriminating colours in the red-orange spectrum. Thanks to the enhanced red vision in females, it allowed them to better distinguish berries and foliage when they were gathering food. Of course, we have to suppose that it's the females who did the gathering in prehistoric times. I won't argue.