Back to the fuchsia: the evolution of colour sensitivity
Have Timeline Colour Researchers The Of Reptiles Of Users Plotting And Vision: Evolutionary Arizona The Birds, Vision Butterflies, Colour Are Been Of Fish, University Greatest
Nothing is in the intellect that was not first in the senses — John Locke
The souks of North Africa are colourful places. We Europeans, Michael Portillo apart, dress more soberly. Military camouflage supresses it, but colour is a powerful weapon. Its origin and nature, however, remain mysterious.
For Locke, the father of empiricism, objects have shape and volume, but they are not actually red, green, or blue. These colour sensations exist only in the eye of the beholder. Light with a wavelength of 400 nanometres triggers our perception of violet, 700nm light gives us red. The colours of the rainbow are generated between these wavelengths. Ours is a virtual reality version of the external world.
Locke’s thesis seems self-evident nowadays, but it must have appeared outlandish when he published it in 1689. Little was known back then about human, or animal, perception. We now know that colour sensation differs between species. An elephant sees the world in shades of blue and yellow. A blue whale doesn’t see the sky as blue. A bumble bee can’t detect redness, although it responds to ultraviolet light invisible to our eyes. The phrase ‘a red rag to a bull’ is nonsensical — bulls are colour-blind.
But why, and when, did colour sensitivity evolve?
From @uarizona: color vision evolved millions of years before genetic color traits in plants & animals. Later, use of color exploded as warning signals in animals, attraction in plants & sexual color traits in vertebrates. @UofAEEB @ZachEmberts@Wiley: https://t.co/n2BhmrHjHP pic.twitter.com/X2lxQSh9NB
— Michael F. Chiang, MD (@NEIDirector) November 15, 2024
Researchers from the University of Arizona have been investigating.
- Gaudy flowers inform insects that a juicy nectar bribe is on offer, in return for their pollen courier services.
- Their clients, the bees and butterflies, need colour vision to find the right flowers to feed on.
- The wasp’s striped yellow outfit is a nuclear deterrent; ‘mess with me at your peril’ it warns.
- The hoverfly, which has no sting, dresses up as a wasp to fool its enemies.
- A peacock’s flamboyant tail proclaims his desirability as a potential mate.
- Parrots, which used perch on pirates’ shoulders, have at their disposal the widest range of colour options in the bird world.
In a paper just published, the Arizona researchers say that it didn’t. They plotted the evolutionary timeline of colour vision. It had emerged, they claim, about 200 million years before flowers and fruits began exploiting it.
Warning colour signals are about five times more common than sexual selection ones. The reason is that creatures such as snakes and poison frogs don’t need to be able to see colours themselves in order to use them... their signals are addressed to potential enemies which can see them.
Even species with poor colour vision may use it for defence. Colourful fruits first appeared around 350 million years ago. Animals did not begin using colour for sexual selection until about 150 million years later.
There has been a dramatic explosion in the use of colour vision during the last 100 million years. Its greatest users are fish, birds, butterflies, and reptiles. Furry mammals are less enthusiastic about colour — they prefer scent, another of Locke’s ‘secondary qualities’.
"Colours, like features, follow the changes of the emotions" — Pablo Picasso.