Psychedelic Dinosaurs, Four-Dimensional Hummingbirds, and How We Got Our Vision: Color, Consciousness, and the Dazzling Universe of Tetrachromacy


“When we pay attention to other animals, our own world expands and deepens.”


Psychedelic Dinosaurs, Four-Dimensional Hummingbirds, and How We Got Our Vision: Color, Consciousness, and the Dazzling Universe of Tetrachromacy

Life would not be possible without color. I mean this both existentially and evolutionarily: Color is not only our primary sensorium of beauty — that aesthetic rapture without which life would be a desert of the soul — but color is how we came to exist in the first place. Our perception of color, like our entire perceptual experience, is part of our creaturely inheritance and bounded by it — experience that differs wildly from that of other species, and even varies vastly within our own species. That limitation offers a golden opportunity to grasp the fundamentals of human nature and reach other sensory levels than we are capable of imagining.

This is the invitation Ed Yong — one of the most insightful science writers of our time, and one of the most soulful — extends in An Immense World: How Animal Senses Reveal the Hidden Realms Around Us (public library), appropriately titled after a verse by William Blake:

How do you know but ev’ry Bird that cuts the airy way,
Is an immense world of delight, clos’d by your senses five?

A quarter millennium of science after Blake — a quarter millennium of magnifying delight through the lens of knowledge — Yong writes:

Earth is filled with textures and sights, sounds, vibrations, tastes and smells as well as electric and magnetic fields. But every animal can only tap into a small fraction of reality’s fullness. Each animal can perceive only a fraction of the world outside its sensory bubble.

Color wheel based on the classification system of the French chemist Michel Eugène Chevreul from Les phénomènes de la physique by Amédée Guillemin, 1882. This print is also available as stationery cards.

Keep your eyes peeled for Umwelt — that lovely German word for the sensory bubble each creature inhabits, both limiting and defining its perceptual reality — he adds:

Our Umwelt is still limited; it just doesn’t FeelIt is that simple. For us it seems all-encompassing. We mistakenly believe it is all we know. This illusion is shared by every animal.

[…]

It is impossible to sense all things, but it does not matter. This is the reason Umwelten are even possible. The act of contemplating an Umwelt other creature’s environment is deeply personal and profound. The information we receive is filtered through our senses. It is up to us to choose what we want.

We are insentient to myriad realities readily available to our fellow creatures — the temperature currents by which a fly, Blake’s supreme existentialist, navigates the air; the ultrasonic calls with which hummingbirds hover between science and magic; the magnetic fields by which nightingales migrate. Yong wrote this with the perspective that only science can give.

Because the Umwelt concept implies every creature must be contained within its own house, it can seem restrictive. To me the concept is a wonderful expansion. It says that there is more to life than meets the eye and that our experience of reality is just a partial view. could experience. It reminds us of the light and darkness that exist, along with noise and silence. Richness is found in all things. It hints at flickers of the unfamiliar in the familiar, of the extraordinary in the everyday, of magnificence in mundanity… When we pay attention to other animals, our own world expands and deepens.

No corner of the house of the senses is more fascinating — for its aesthetic gifts, its evolutionary convolutions, and its almost spiritual effects — than color.

One of Goethe’s geometric studies of color perception

“Color itself is a degree of darkness,” Goethe wrote in his poetic theory of color and emotion. This statement is a fitting description of evolutionary history of color vision, despite the fact that it was disproven by science and rewritten by scientists who were inspired by it.

To see at all, ancient animals developed a type of protein receptor called opsin, which patrols the surface of the cell that contains it — a type of cell called a cone — and grabs at light-absorbing molecules, forming a partnership that sparks the chemical reaction of electrical signals that carry vital information to neurons — information which resolves in what we call vision. Our primordial ancestors experienced a profound confusion 500 million years ago when they moved from deep under the sea to shallower waters. This was because sunlight danced on the surface and reflected into the water. One single area of visible space suddenly became so bright that it could change its brightness 100 times per second under the flickering sunrays. It became difficult to distinguish predator and prey against this flashing strobe attack.

Our monochromatic ancestors had to be able to detect binary variations in brightness and dark to cope with dangerous disorientation. Cones and their opsins grew more and more specialized, with different types emerging to absorb different wavelengths of light — long, which we perceive as red, medium for green, and short for blue. A complex neural network emerged to compute these comparisons — neurons excited by some cones but inhibited by others, allowing creatures to detect particular colors, indistinguishable by degrees of darkness in monochromatic vision — certain shades of red and green can (and do, to the red-green colorblind) look identical in grayscale.

This is known as opponencyThis is what gives us all our color vision. The opsins are different in each animal, making color perception a subjective experience.

“Spectra of various light sources, solar, stellar, metallic, gaseous, electric” from Les phénomènes de la physique by Amédée Guillemin, 1882. This document is also available as a printed copy and stationery cards.

The color of our own animals’ experience of colors, which is as essential to our consciousness and as important as it might be, was acquired quite randomly by an amazing accident of evolutionary evolution. (Then again, we could say the same of consciousness itself, and perhaps of all of life — none of it was inevitable, none part of some grand score for the symphony of chance.) Yong writes

Nearly all primates that emerged were dichromatic. There were two types of cones: short and long. The way they saw was in the same manner as dogs: They could see in both blues and yellows. A rare accident took place between 29-43 million years ago. It permanently altered the Umwelt for one particular lineage of primates. The extra gene which builds long opsin was given to them. This is often the result of cells dividing and copying DNA. They’re mistakes, but fortuitous ones, for they provide a redundant copy of a gene that evolution can tinker with without disrupting the work of the original. That’s exactly what happened with the long-opsin gene. The one copy that absorbed light at 560 nanometers was the most stable. One of the copies gradually changed to absorb light at a shorter wavelength, 530 nanometers. This is now called medium (or green) opsin. They are 99 percent identical. However, the 2 percent gap between the two is the difference in seeing blues and yellows as well as adding reds or greens to this mix. These primates were able to develop trichromacy thanks to the addition of the medium opsins, which joined the shorter and longer ones. And they passed their expanded vision to their descendants — the monkeys and apes of Africa, Asia, and Europe, a group that includes us.

Our rainbow was suddenly multiplied by the accidental duplication of long-opsin genes

Monochromats can distinguish between about 100 grades of gray, black or white. The dichromat takes around 100 steps to go from yellow to white, and multiplies the grays to make tens of millions of colors. A trichromat adds another hundred or so steps from red to green, which multiplies again with a dichromat’s set to boost the color count into the millions. Every additional opsin multiplies the visual palette by exponentially.

Imagine a magician sweeping over a dichromat who can only see 1% of what a tetrachromat can see, adding an additional cone to the magic wand, and the result would be a complete revolution in reality. This would happen, if our perceptions were stronger than our frames of reference. (Thoreau captured this haunting aspect of the animal soul when he observed that “we hear and apprehend only what we already half know.”) When researchers took this fortuitous long-opsin gene that chance handed humans and gave it to a pair of squirrel monkeys, dichromatic by nature, the monkeys gained instant access to a world a hundred times more colorful. They didn’t wander wonder-stricken though this new land, taking in every unexpected green leaf or every red berry. Instead, they lived their everyday lives as normal, showing the relativity to wonder. Yong reflects

Seeing more colors isn’t advantageous in and of itself. The magic of colors is not inherent to them. When animals take meaning from colors, they become magical. Because we have inherited their ability to see colors from trichromatic ancestors and given them meaning, some are unique to us. Conversely, there are colors that don’t matter to us at all. Some colors are not even visible to us.

Vivian Torrence created Art for Chemistry Imagined by Nobel laureate Roald Höfmann.

Our species’ distinctive trait may be our insatiable curiosity about the unknown and undiscovered. It is this longing, whether we call it curiosity, imagination or both, that drives all creative endeavors in science and art. This is the place where the chromatic equation becomes infinitely fascinating.

The story began back in 1880s when John Lubbock, a polymathic banker, scientist, and philanthropist, shined a beam through a prism and split the light into the constituent colors. This rainbow fell onto some ants. As expected, they fled from light. Unexpectedly they ran for colors that he could not see, but also from a patch at the violet end which seemed completely dark. This was the discovery of the ultraviolet range of the electromagnetic spectrum — light with wavelengths between 10 to 400 nanometers, too short for the human eye to detect.

Blues from the Werner’s Nomenclature of Colours: Adapted to Zoology, Botany, Chemistry, Mineralogy, Anatomy, and the Arts, which inspired Darwin. You can also get a printed version and a face-mask.

This was an era when science still clung to the dangerous Cartesian binary of human exceptionalism, under which other animals experienced the world either exactly as we do or in greatly diminished ways — non-human animals were thought to either see the same rainbow we do or to be entirely colorblind. The notion that they could see color, and see it differently than we do, and see what we cannot see, was a radical demolition of dogma — too radical to fully accept. For a long while, ants were thought to be exceptional in the animal kingdom — fortunate flukes unrepresentative of the sub-human whole. Then, eventually, the bees joined them.

But then, in a mere century of science — a blink of evolutionary time — numerous birds, fish, reptiles, and insects were reluctantly admitted into the UV-sighted ranks. Still, we excluded mammals from the realm of possibility — this is the history of our species — until, in a humbling testament to Richard Feynman’s insistence that the imagination of nature will always exceed that of the human animal, a team of scientists discovered a short cone tuned to UV light in three species of rodents. Within half a human generation, many mammals — including dogs, cats, reindeer, cows, and ferrets — were discovered to detect UV light with their short blue cones.

We know now that ultraviolet is visible to most animals. Unfortunately, we are one of those unfortunate flukes.

Even some human animals — those who have had their lenses damaged in some way — can perceive the UV end of the spectrum as a pale blue, none more famous than Claude Monet and his water lilies, the dazzling product of his refusal to have his cataracts — a progressive clouding of the lens that filters color — surgically removed; instead, he went on painting the world as he saw it, increasingly warping the electromagnetic spectrum into otherworldly colors.

Claude Monet: The Water Lilies – Setting Sun, 1915-1926. (Musée de l’Orangerie, Paris.)

With an eye to bees — tetrachromats with opsins most tuned to blue, green, and ultraviolet — Yong winks at our human tendency toward self-reference and celebrates the supreme gift of science, that of achieving perspective:

If bees were scientists, they might marvel at the color we know as red, which they cannot see and which they might call “ultrayellow.” They might assert at first that other creatures can’t see ultrayellow, and then later wonder why so many do. You might wonder if this is a unique color. You might see roses in ultrayellow camera and they will rhapsodize over how much different they are. It is possible that large bipedal creatures who see the color might exchange secrets through their flushed faces. It might be that they realize it’s just another color. This is primarily because their eyes cannot see it. They might also wonder how it would feel to have it in their Umwelt to enhance their three-dimensional color palette.

The electromagnetic spectrum has merely shifted the bees’ trichromatic nature to one another, however. The truly mind-bending part — quite literally, for it flexes our cognitive capacity for imagination beyond the hard-wired perceptual limits of our consciousness — is when we raise color vision by another order of magnitude, to tetrachromacy: the addition of a whole other cone with a whole other opsin. As in the transition from dichromacy and trichromacy, the trichromat only sees 1% of all the colors available to the tetrachromat. It is almost certain that Dinosaurs were tetrachromats. They lived in an enchanted primordial land. Hummingbirds — those feathered miniature heirs of the bygone giant reptiles — are tetrachromats. Hummingbirds can see millions upon millions of colors, and they are able to distinguish among flowers of similar hues.

One of artist Rosalind Hobley’s stunning cyanotype portraits of flowers, which rely on a chemical process sensitive to light on the edge of blue and ultraviolet

But for a trichromat to imagine tetrachromacy is as challenging as for a two-dimensional creature to imagine a three-dimensional world — we inhabit a chromatic Flatland, in which the vision of a hummingbird remains to us as enticing and elusive an abstraction as a Klein bottle.

Yong writes

[Hummingbirds] don’t just have human vision plus ultraviolet, or bee vision plus red. Tetrachromacy doesn’t just widen the visible spectrum at its margins. This unlocks new possibilities dimensionThere are many colors.

[…]

Think of trichromatic human vision in the form of a triangle. The three corners represent our blue, green, or red cones. Any color we are able to see is a combination of these three colors. Each point can then be plotted in that triangular area. By comparison, a bird’s color vision is a pyramid, with four corners representing each of its four cones. The entire space of our color vision is only one side of this pyramid. Its vast interior contains colors that are not accessible to many of us.

Rucker’s Hermit Hummingbird by John Gould, 1861. This print is also available as stationery cards and a printed version. All proceeds go to the Nature Conservancy.

In a wonderfully Dr. Seussian passage, Yong sums up the revolutionary discoveries of violinist turned sensory ecologist and evolutionary biologist Mary Caswell “Cassie” Stoddard, who spearheaded the hummingbird research:

If our red and blue cones are stimulated together, we see purple — a color that doesn’t exist in the rainbow and that can’t be represented by a single wavelength of light. Non-spectral colors include these combinations. The four cones of the Hummingbird can help them see more, which includes UV-red (which is green + UV), UV-yellow, UV–green (which red + UV + UV), as well as UV-purple, which is red + UV + UV). At my wife’s suggestion, and to Stoddard’s delight, I’m going to call these rurple, grurple, yurple, and ultrapurple. Stoddard discovered that non-spectral colors, and their many shades, account for about a third to the color found in plants and feathers. Meadows, forests, and other natural areas are filled with grurples or yurples to a bird. To a broad-tailed hummingbird, the bright magenta feathers of the male’s bib are actually ultrapurple.

[…]

Violinist [Stoddard]It is known that the sounds of two notes played simultaneously may sound distinct or combined into totally new tones. As an example, hummingbirds may perceive purple as being a mix of UV and red or as a completely new hue. When they make choices about which flowers to visit, “do they group rurple with reds, or do they see it as an entirely different hue?” she asks. They can tell that it’s different from pure red, “but I can’t articulate what it looks like to them.”

Goethe’s color wheel, 1809. Available as a printed version.

Many more ineffable wonders of perception come abloom on the pages of Yong’s An Immense World. This fragment can be complemented by Ellen Meloy, a great natural writer on color and science. Arthur Zajonc is a physicist on consciousness and vision. Alexandra Horowitz, a cognitive scientist on seeing reality beyond our normal perceptions.


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