Do dogs live in a black-and-white world?
As a child, I remember my mother telling me something she learned when she was an eye nurse – dogs are colourblind. Now, if I remember rightly, she didn’t mean they could only see in black and white as research in the 1940s had suggested, but that they had limited receptivity to the full colour palate. They were red-green colourblind, like some boys and men. The issue came up after they tested us boys at school for colour blindness with those spotty number colour charts.
However, proof that the canine world isn’t monochrome didn’t come until 1989, so my mother, as was often the way, was way ahead of her time. Anyway, that proof demonstrated that dogs have dichromatic eyes. They have two types of colour receptor, cones, in the retinas of their eyes based on two pigments. Specifically, they can see various colours just not as many as the average human.
People are generally trichomats, they have three colour receptors, for red, green, and blue and a set of combinations thereof. For most people, there are lots of colours in between the violet, indigo, blue, green, yellow, orange, and red of the rainbow. Although, as I’ve mentioned before while not everyone agrees on the existence of indigo, there really is a much greater gamut of colours in there! Generally, we can discern a million or so colours, hence the seemingly endless parade of options when choosing paint with which to decorate your house.
Dogs have much more limited decorating options, but some women have many more. They are tetrachromats. Some girls and women have four colour receptors in their eyes allowing them to see almost 10 million colours, an order of magnitude more colours than most boys and men and other trichromatic females. Ironically, the fathers and sometimes at least one son of these tetrachromat females with their super-vision are usually colour blind. It’s all about the genes.
Incidentally, we now know that fish, reptiles, and birds are commonly tetrachromats. Some species not only have a greater palate and can distinguish between subtle hues in the visible spectrum, but many can see light beyond the rainbow and into the ultraviolet part of the spectrum. Conversely, many mammals, especially nocturnal and crepuscular species, have through evolution lost two of their colour receptors in favour of greater low-light visual acuity and so, like dogs have a limited colour palate. The ancestors of primates were dichromats, but that third pigment later re-emerged in primates, including humans, and was perhaps a response to fruit eating. The fourth pigment re-emerged in some females.
But, even tetrachromacy is not really super-vision. Some insects, such as the odonata, dragonflies and damselflies, have even more colour pigment receptors in their compound eyes. Research suggests that they have between 15 and 33 genes for visual pigments. The colour palate of their vision could be way, way more detailed than that of even tetrachromat women, they can discern millions and millions of hues.
The issue of canine vision went viral on social media recently and I suspect at least one person would’ve alluded to dogs seeing just fifty shades of grey…
The question of my blog post title was a QTWTAIN, a question to which the answer is no. No, dogs do not live in a black and white world, they see colours, but just not as many as most men, some women, and definitely not that Emperor dragonfly that was darting about our garden pond in the summer.