Cryptochromes (from the Greek κρυπτός χρώμα, ‘hidden colour’) are a class of flavoproteins found in plants and animals that are sensitive to blue light.
A Case Of The Blues
Cryptochromes (CRY) are interesting because they are photosensory receptors that regulate growth and development in plants (in response to light), and are involved in the circadian rhythms and the sensing of magnetic fields (magnetoreception) in a number of species, including humans.
The two genes Cry1 and Cry2 code the two cryptochrome proteins CRY1 and CRY2. They are evolutionarily highly conserved proteins that belong to a flavoproteins superfamily existing in all kingdoms of life (suggesting they are super useful). Cryptochromes are derived from and closely related to photolyases, which are bacterial enzymes that are activated by light and involved in the repair of UV-induced DNA damage. However, in eukaryotes, they no longer retain this original enzymatic activity. So what do they do with all that blue?
When it comes to plant growth: despite much research on the topic, exactly how cryptochromes regulate growth and development (including seeding and flowering) is still poorly understood. Past studies have supported a model by which the light energy captured produces an epigenetic response (changes in gene expression in response to environmental stimuli). However depending on the plant species and context, there are many alternative hypotheses for mechanism of action.
In circadian rhythms: nearly all living organisms use daily patterns of day and night to entrain their endogenous circadian clocks – this involves input from the eyes and other organs. In this sense, there is evidence of an inherited clock mechanism that allows us to be organically entangled in a lightly lucid dance.
Magnetoreception is a sense which allows an organism to detect a magnetic field to perceive direction, altitude or location – for example when birds migrate.
Over the last three decades, evidence has emerged that low-intensity magnetic fields can influence biological systems. It has been reported that power lines are associated with childhood leukemia and that pulsed magnetic fields increase the production of reactive oxidative species in cellular systems. Studies in this field have been viewed with scepticism, as reproducible molecular mechanisms are unidentifiable.
The human body produces complex electrical activity in several different types of cells. This includes neurons, endocrine, and muscle cells – otherwise known as excitable cells. This electricity creates the aura of an electromagnetic field. However the role of cryptochrome here is undetermined.
A more favourable contender is currently magnetite, an iron mineral found in our brains, according to biophysicist Joe Kirschvink at the California Institute of Technology (Caltech) – a search party veteran – this exposes us to questions such as whether or not a subconscious magnetic sense affects human behaviour.
The mechanism of magnetoreception is only settled for certain bacteria, which harbour magnetite crystals that align with the Earth’s magnetic field. Bird beaks and fish snouts also contain magnetite. In humans, it has recently been found that it is most concentrated in lower, evolutionarily ancient regions: the brain stem and cerebellum. But there has been no identification of proposed sensory cells that contain magnetite.
It is argued that magnetite, like a compass needle, responds to a field’s direction, whereas cryptochrome (as found in the retina) responds identically to fields with opposite polarity. In looking for a magnetosensory system, scientists are searching for evidence that the brain actively processes magnetic information in a way that influences behaviour, as opposed to being passively affected by it.
The Sensory Science Spectrum
Maria Michela Sassi is a professor of ancient philosophy at Pisa University. She has written a number of essays on diverse topics in ancient thought, from pre-Socratic philosophy to Aristotle, and is the author of The Science of Man in Ancient Greece.
She explains that Homer used two adjectives to describe aspects of the colour blue: kuaneos, to denote a dark shade of blue merging into black; and glaukos, to describe a sort of ‘blue-grey’, notably used in Athena’s epithet glaukopis, her ‘grey-gleaming eyes’. He describes the sky as big, starry, or of iron or bronze (because of its solid fixity). The tints of a rough sea range from ‘whitish’ (polios) and ‘blue-grey’ (glaukos) to deep blue and almost black (kuaneos, melas).
The sea in its calm expanse is said to be ‘pansy-like’ (ioeides), ‘wine-like’ (oinops), or purple (porphureos). But whether sea or sky, it is never just basic ‘blue’. The ancient Greek experience of colour does not seem to match our own. In a well-known aphorism, Friedrich Nietzsche captures the strangeness of the Greek colour vocabulary:
How differently the Greeks must have viewed their natural world, since their eyes were blind to blue and green, and they would see instead of the former a deeper brown, and yellow instead of the latter (and for instance they also would use the same word for the colour of dark hair, that of the corn-flower, and that of the southern sea; and again, they would employ exactly the same word for the colour of the greenest plants and of the human skin, of honey and of the yellow resins: so that their greatest painters reproduced the world they lived in only in black, white, red, and yellow.
Poet, philosopher and statesman, Johann Wolfgang von Goethe also observed these features of Greek chromatic vision. Goethe underpinned his judgment through a careful examination of the theories on vision and colours elaborated by the Greek philosophers, such as Empedocles, Plato and Aristotle, who attributed an active role to the visual organ, equipped with light coming out of the eye and interacting with daylight so as to generate the complete range of colours.
Goethe also noted that ancient colour theorists tended to derive colours from a mixture of black and white, which are placed on the two opposite poles of light and dark, and yet are still called ‘colours’. The ancient conception of black and white as colours (often primary colours) differs from Isaac Newton’s experiments on the decomposition of light by refraction through a prism. The common view today is that white light is colourless and arises from the sum of all the hues of the spectrum, whereas black is its absence.
Goethe set the Greeks’ approach to colour against Newton’s by highlighting that it encapsulates the subjective side of colour perception. He considered the Newtonian theory to be a mathematical abstraction in contrast with the testimony of the eyes, and thus downright absurd. For Goethe, Newton’s dark room was a kind of prison for the imagination. In contrast, Goethe studied the eye’s changing responses and highlighted the association between colour and emotion.
Although Goethe’s work was dismissed by many physicists, it was taken seriously by many artists and philosophers, such as Turner and Kandinsky, Schopenhauer and Wittgenstein. Today it is accepted that every culture has its own way of naming and categorising colours – due not just to varying anatomical structures of the human eye, but to the fact that different ocular areas are stimulated, which triggers different emotional responses, and offers findings that are translated through different cultural contexts.
There is a specific Greek chromatic culture, just as there is an Egyptian one, an Indian one, and a European one – each of them being reflected in a vocabulary that has its own peculiarity, and is not to be measured only by the scientific meter of a Newtonian paradigm.
Subjective Subconscious Bias
In 1898, American artist Albert Henry Munsell created a ‘colourimetric system’ based on a Colour Sphere. According to this model, any colour sensation can be defined through three interacting aspects: the hue, determined by the position in the Newtonian spectrum, by which we discriminate one colour from another; the value or lightness, ranging from white to black; and the chroma, which corresponds to the purity or saturation of the colour, depending on the wavelength distribution of light.
Add to these the concept of saliency, that is, the capacity of a colour to catch visual attention, and the defective definition of blue and green that may be interpreted as a symptom of colour-blindness can be explained since the linguistic definition of hue is proportionate to the saliency of a colour. The Greeks were perfectly able to perceive the blue tint, but were not particularly interested in describing the base blue tone of sky or sea – at least not in the same way as we are, with our modern sensibility.
This model is helpful for describing the different ways in which a chromatic culture can segment the huge range of possible combinations of the three dimensions by privileging one or the other. A culture might emphasise hue or chroma or value, each with varying intensity. And so the Munsell model is useful in that it helps to demonstrate the remarkable Greek predilection for brightness, and the fact that the Greeks experienced colours in degrees of lightness and darkness rather than in terms of hue.
For the Greeks, colour was a basic unit of information necessary to understanding the world, above all the behavioural world. One’s complexion was a major criterion of social identity, so much so that contrasting light women and dark men was a widespread cliché in Greek literature and iconography, rooted in the prejudice that the pale complexion of women is due to their living in the darkness of the domestic sphere, whereas men are tanned and strengthened by physical exertion and outdoor sports. So the Greek word chroa/chroiá means both the coloured surface of a thing and the colour itself, and is significantly related to chros, which means ‘skin’ and ‘skin colour’. The social and ethical values of colour cannot be forgotten in trying to discern Greek chromatic culture.
Of use are two further parameters, in addition to the Munsell model and the subjective value of colour. There is the glitter effect of colour, which is produced by the interplay of the texture of the object and the light conditions, and there is the material or technological process by which a certain colour is obtained in the practice of painters and dyers. With these in hand, the full range of Greek colours comes into view – even the notorious ‘curious case’ of porphureos, the chromatic term most difficult to grasp.
Not only does porphureos not correspond to any definite hue, placed as it is on the borderline between red and blue (in Newtonian terms), but it is often applied to objects that do not appear straightforwardly ‘purple’, as in the case of the sea. When the sea is called porphureos, what is described is a mix of brightness and movement, changing according to the light conditions at different hours of the day and with different weather, which was the aspect of the sea that most attracted Greek sensitivity.
In trying to expose the hidden, and to see the world through ancient eyes, a reductionist lens is limited by more than logic and language. Dynamic multidimensional colour theories reach out to a holistic experience with a chromatic vocabulary beyond an island science. Using just the mathematical abstractions of Newton’s optics, we do not illuminate the horizons of our imaginations with what the Greeks saw when they stood on their shores, gazing out upon the porphureos sea, where the celestial meets the terrestrial.