Why we see red so vividly

Red amongst green

Have you ever noticed that the colour red seems to stand out prominently amongst other colours and wondered why? Have you perhaps observed that brands such as McDonalds, British Airways, Target, Qantas, CNN, Kentucky Fried Chicken, and YouTube use red as part of their logo, or that the Specials tags in supermarkets are nearly always red? Ever stopped (see what I am doing here?) and thought about why red is used as the most important colour at traffic lights and wondered why red cars go faster? Actually, I can’t help with the last one… but read on to find the answers to all the other questions.

Primates are the only mammals that see red. Human eyes, like chimp eyes, probably evolved to see red because of our frugivore ancestors. The reason we can see red, and see it so vividly, is because of the interplay between three types of cone cells in the retina, of which each has a pigment responsive to light from different sections of the visual spectrum: red, green, and blue. Because humans have this three-cone system, we can see more than 2.3 million gradations of colour. In fact, we are so sensitive to the greens and reds in the spectrum that we can pick up colours with only one per cent variance in wavelength.

Our ancestors (we are talking way back – not Grandma), like most mammals now (including your pet dog and cat), saw the world in dichromatic vision – only greens and blues. Somewhere along the way (about thirty or forty million years back), a mutation in the gene for a light-receptor protein shifted its sensitivity from green light to red. Although it was a small change, it was significant enough to give our primate ancestors an advantage when they were seeking food – with the red pigment they were able to pick out ripe fruits amongst the green foliage. Scientists also suggest that the enhanced vision meant that we could also distinguish other important objects that may have been hanging around in the foliage, such as brightly coloured venomous snakes.

Even within this spectrum, new research suggests that we all see hues differently, and that a significant proportion of women have more distinctive colour vision than men, because they possess an extra red photopigment. If this is the case, then these women are able to distinguish colour differences that look indentical to the rest of us.

Sources:
NJ Dominy and P Lucas, 2001, “The ecological importance of trichromatic colour vision in primates”, Nature 410, 363-66.
LA Isbell, 2006, “Snakes as agents of evolutionary change in primate brains”, Journal of Human Evolution 51, 1-35.
K Jameson et al., 2001, “Richer color experience in observers with multiple photopigment opsin genes”, Psychonomic Bulletin and Review 8 (2), 244-61.
J Ackerman, 2008, Sex, Sleep, Eat, Drink, Dream, Scribe Publications: Melbourne.