Intelligent Design in Color Vision — A Gift to Us
Recently, I came across a display of flowers that seemed to pulsate with colors spanning the visible spectrum — from deep red to purple, and multiple shades in between. My physicist brain began to think of the colors in terms of their wavelengths and it struck me how this gorgeous frolic across the visible spectrum actually only covered wavelengths differing in value by less than a factor of two. From about 400 nanometers to 700 nanometers, this narrow slice of the electromagnetic spectrum offers us every color we perceive with our eyes.
If we compare a similar wavelength range of sound waves, a difference of a factor of two spans just a single octave. I think it’s fair to say that our auditory perception of the range of notes spanning an octave doesn’t begin to give us such a dramatic sense of variety as the spectrum of colors seen in the accompanying photo of the array of flowers.
Why the Difference?
Perhaps we are seeing further evidence of design built into our sense of sight. The laws of physics in conjunction with biochemistry set up the limitations on the range of wavelengths we can perceive with our vision. Visible light, seen as red (around 700 nm), orange, yellow, green blue, and violet (about 400 nm) is the only portion of the entire electromagnetic spectrum that could serve as the basis of our gift of sight. The photosensitive molecules in the rods and cones of the retinas of our eyes would either be inactivated or destroyed by light with longer or shorter wavelengths, respectively.1 Sunlight peaks in intensity near the middle of the visible portion of the spectrum, and Earth’s atmosphere has a narrow window of transparency covering the range of visible light. Water, whether as vapor in the atmosphere or as the fluid within our eyes through which light must pass, also possesses a remarkably sharp drop in its absorption just in the range of the colors of sight.
The Most Important Sense
Consider that since sight is arguably the most important of our five senses, and since the laws of physics and chemistry limit the feasibility of sight to such an extremely narrow range of the electromagnetic spectrum, a design feature we can be thankful for is the rich association of vibrant hues of color perceived with just minor variations in wavelength across the visible range.
In an earlier article (“Thank God for Quantum Mechanics”), I highlighted one of the aspects of the quantum nature of reality that allows life—namely the wavelike nature of particles that facilitate the production of sunlight via nuclear fusion reactions in the core of our star. At the receiving end of sunlight, as it contributes to our gift of sight, the quantum nature of light itself becomes an essential factor in our ability to see. Michael Denton, in his book Children of Light, points out that while the ability of our eyes to form a focused image relies upon the wave nature of light, the ability of the photoreceptive molecules in our retinas to detect incoming light relies upon the quantum nature of light.
Light’s Dual Aspect
In the quantum or photon view of light, the energy of a light wave is delivered in quantized packets of energy, called photons. The energy of each photon is inversely proportional to the wavelength of the light wave. It’s the quantum nature of visible light that enables it to deliver a bullet-like packet of energy to the nanoscale photoreceptive molecules in the rods and cones of our eyes. Without this dual aspect of light, our sense of sight would be as limited as our skin’s ability to detect variations in ambient temperature.
Waves, photons, photoreceptors — do these features of physical reality explain our vivid awareness of colors in how we “see” small variations of optical wavelengths? In my understanding of electromagnetic radiation, there is nothing intrinsically a part of light in the visible spectrum that carries the attributes of “green” or “red.” The approximately six million cones in the retina of the human eye come in three different varieties, each one exhibiting optical sensitivity across overlapping wavelength ranges spanning the visible spectrum.2 When photons of different optical wavelengths impinge on the photosensitive molecules in these cones, they induce electrochemical changes that stimulate the optical nerve connecting our eyes to our brain.
Still, the question remains, where, for example, does the color violet come from in our perception of an array of flowers? What produces the palette of greens that we see when viewing grass and trees? Again, nothing in the physics of light or our retina’s biochemical response to light is inherently connected with the colors we perceive. And yet, color sense is an almost universal human phenomenon that has both practical and aesthetic value for us.
A World in Grey
How different our perception of reality would be if our brains processed visual signals from the optical nerve as only varying shades of beige or pink or grey! A certain percentage (up to 8 percent) of people have a type of color vision deficiency (CVD), preventing them from distinguishing between particular colors, usually caused by one or more photoreceptive molecules being absent or non-functional.3 CVDs are noted in comparison to normal human vision. But what if everyone had what we consider complete color blindness, perceiving only shades of grey — would we even be aware of the existence of color, or would we even be able to imagine it?
From the dual nature of light — behaving both as a wave and a photon — to the ability of visible light to initiate the photochemical transformations within our eyes, to our brains’ perception of optical signals as vividly varying colors, to our aesthetic appreciation of the hues composing our visible world, the gift of sight manifests design of the highest order. To borrow a remark by physicist Eugene Wigner, made in a different context, our perception of color “is a wonderful gift which we neither understand nor deserve.”4
