Chromatophores - of chameleons & cuttlefish cousins

Chromatophores are highly specialized cells that allow an organism to change the hues and patterns of its skin.  Examples of this trait in species distantly related across the genetic tree of life, living in very different environments, argues in support of natural selection and the theory of evolution.

The chromatophores in the skin of many cephalopods exhibit polychromatism. As an example of the common mechanism, Loligo pealeii color cells are manipulated by a wagon-wheel of muscles (between 15 and 25) that encircle and stretch the central, elastic pigment sac, pulling it from a tiny sphere into a disc; typical relaxed sphere diameters of 10-100 µm contrast with 0.1-1 mm when flattened into discs. When these muscles relax, the sac recovers its original shape1. Various colors of pigment sac exist, each with a specific layer and size of chromatophore: yellow rates smallest, brown the largest. The sac transition from “off” to “on” requires approximately 700 milliseconds, and Japanese researchers propose that Sepioteuthis lessonianas' enjoys direct control over its body color and pattern, as neural signal frequencies correspond to shifts.2

The chromatophores in the skin of many lizards of family Chamaeleonidae accomplish color and pattern change in a very different way. Pigments in these cells are stored in fatty sacs called vesicles, and are not manipulated by muscles but by hormonal domino effects.  Chameleon chromatophores release their stockpiled vesicles when triggered by these chemicals, which drift about and soon burst, scattering “dye” molecules throughout the cell to temporarily alter its color. Below a transparent outer skin layer, these pigment cells are stacked vertically with respect to their vesicle “paint palette”. Yellow xanthophores are topmost, followed by red erythrophores, blue iridiphores (which use guanine as their “paint”), then finally melanophores, employing melanin to create browns and blacks. Amazingly, this dying process is additive, with greens and oranges possible from xanthophores reacting in sync with iridiphores and erythrophores.3

Both of these far-removed families of organisms utilize endogenous dyes, but this is where their isomorphism ends.  Chameleons alter integument by expending and mixing vibrant chemicals, while octopi, cuttlefish and squid are more economical, having devised stretchy, reusable pigment sacs to unfurl with motor impulses. The “bombs of paint” technique versus the “hoist the flag” approach is a fascinating example of widely divergent evolutionary lines selecting similar color-altering talents, yet employing very different cell designs in the two. The hypothetical direct neural control seen in cephalopods further contrasts with the endocrine and limbic drivers in Chamaeleonidae chromatophores; such structural control differences suggest intentional color shifts in the former, versus emotional and reactive in the latter. Yet regardless of the regulation of these two systems, their similar function supports the claim that natural selection yields maximally efficient, and often convergent, structures.

1. Macroscale and Microscale Structural Characterization of Cephalopod Chromatophores.

Keith M. Kirkwood, Eric D. Wetzel, George Bell, Alan M. Kuzirian, and Roger T. Hanlon

Proceedings of the Army Science Conference, Orlando, FL, 29 November 2010.

2. Suzuki, M., Kimura, T., Ogawa, H., Hotta, K., & Oka, K. (2011). Chromatophore Activity during Natural Pattern Expression by the Squid Sepioteuthis lessoniana: Contributions of Miniature Oscillation. Plos ONE, 6(4), 1-8. doi:10.1371/journal.pone.0018244

3. High Dynamic Range Image rendering of color in chameleons' camouflage using optical thin films. Mark Prusten.  Proc. SPIE 7057, The Nature of Light: Light in Nature II, 705709 (August 11, 2008); doi:10.1117/12.802177

Defending Dualism (or not)

Defending dualism requires me to do what what dualist thinkers do, and postulate the existence of a type of matter-energy (proven by extensive physical research to be interchangeable at a primal level, research widely ignored by all but SF authors and New Age gurus) that has not been revealed in any scientific studies to date, ever.  While normally disinclined to shelter exclusively behind the bulwark of empirical thinking, in this case it seems the best and most honest tactic.

What is the numinous mind made of, if not of matter-energy?  And if not matter-energy, then how does it interact with the body that houses it, how does it control organs, eyes, hands or anything whatsoever?  When we spear the monstrous, easily visible neurons of a giant squid, thrusting the talons of scientific inquest into the very fibers of the biological mind, we find little that is different from our own bodies; aside from variations in scale and chemistry, the giant squids are wired very much like the elephants, the ostriches, the polar bears, narwhals, poodles, orangutans, chimpanzees, and humans of this planet.

Why, then, a separate type of elemental matter-energy for the mind?  Plato is one major champion of this dualist position, as he taught that material existence is merely the echo of a far higher state.  Our bodies, according to Platonists, are crude after-images of mystical Forms, things which also inspire music, nature, and all the ‘universal concepts’ of our manifold physical reality.  This type of thinking is possible in a world without modern science, in the Near East of two millennia ago: it seems indefensible in this age of broad physical understanding, when we measure electrochemical impulses across invisibly small gaps in living brains, forge new elements by clever subatomic manipulations.  All is matter-energy, the physicists teach us, and the dynamic, shimmering, self-gazing lattice of loops which we name “mind” is no exception.

Spinoza is fearless in his rejection of Platonic dualism, writing with astounding clarity from pre-Enlightenment Europe in his On the Improvement of the Understanding (1662),

“The properties of things are not understood so long as their essences are unknown.”  He also opined, in correspondence, “we must take care not to admit as true anything which is only probable. For when one falsity has been let in, infinite others follow” (Letter 54).  It is this sort of rigorous intellectual honesty and parsimony of argument that provide the foundations for all the brave investigations that have built our miraculous -yet rational- world of technological wonders.  It is the spirit of material monism, or materialism.  As I am pursuing a Bachelor of Science, and am planning a career in research and design, I cannot seriously endorse any position other than materialism without feeling like a fraud, and without the bile of ingratitude souring my breath.

Everyone's a loser, baby, that's true

So here I am, scribbling up a summary of this ridiculous book on our visual system.  It's a very visceral and vivid piece of writing, and it lends itself well to a sentence-to-page sort of ratio. Yet I'm only a tiny way into it, when I realize- it's all true.

Here's the gist:

Our vision “looks” for four things: the shape, the shiny, the light, and the sight-line. That’s it. These four calculations are what constitute our visual system, sole tenant of our occipital lobe. The early visual system sorts out which changes in these things are due to what reasons, and then creates images in which these reasons are easily distinguished. Got it?


These Four Factors (FFs) are so incredibly significant that our entire visual representation is built around creating them. What you see is a result of How: Shaped, Shiny, Lit, and Seen a surface is. Ah, a surface! you cry. I can grasp what’s going on here. Indeed. The physical aspects of a four-dimensional object are well represented by a model which features the FFs, for Four Factors. So our mammal primate body built us a visual system which understands the FFs.

Stage 1: the Primal Sketch. Vital information such as intensity changes, local geometry, and luminosity are encoded ever so briefly in a rough scrawl. Then, soon after, a bunch of other cool things happen to that Primal Sketch and a 2 ½-D (two-and-a-half dimensional) image is rendered- again, by the weird neurons of the occipital lobe, aka the early vision system, or V1. Then the two sketches are placed atop one another, logically, in a viewer-centric perspective.


Isn't that frustrating? Color doesn't appear until V4, by which point I've almost lost interest.  Yet I'm also reminded of how unabashedly atheistic most of this psychophysics is, and then I keep going.