Some of these resemblances are perfectly staggering—to me they are a source of constant wonder & thrilling delight. It seems to me as though I obtain a glimpse of an intelligent motive pervading nature, as well as of the mighty, never-resting wonder-working laws that regulate all things.
Henry Walter Bates, letter to Darwin, 1861
OF ALL THE FORMS OF PHYSICAL ADAPTATION that play a role in furthering any species’ survival, two stand out by way of sheer sophistication: defense mechanisms and protective coloration. Not just in their sophistication, but with a hard to pin down attribute—a quality of devious genius the English language has no word for.
Plant and animal defenses are often characterized as being products of evolutionary arms races. Nature’s first predator was some single celled organism that hit on the idea of engulfing smaller cells, thereby inventing food. Ever since that game-changing event took place, most living beings have taken part in what amounts to an endless contest where the winners manage to postpone being eaten by running faster, growing thicker shells to thwart increasingly powerful jaws, or simply by going into hiding. Defense mechanisms go well beyond basic, no-frills types of armor like tough skin or sturdy shells. There’s a whole array of spines, spurs, and horny spikes. There are vile excretions and break-away appendages. Biting and stinging double as defensive protection and means for securing prey. Some animals rely on smoke screens, electric shocks, or auto-evisceration. Edible but slow-moving (or resting) creatures often depend on some kind of protective coloration to serve as a warning sign or as camouflage. Many forms of camouflage are breathtaking in their subtlety of rendition, making them among the most dramatic displays of nature’s knack for coming up with inventive solutions.
These attributes have long been a source of wonder and cause for heated debate thanks to a shared quality of appearing intentionally designed in a way that exceeds the appearance of design in other features. Nonetheless, evolutionary biologists maintain that all these things can be accounted for by way of classic Darwinian gradualistic evolution. In spite of this widespread conviction, there are no definitive explanations for marvels that have the appearance of being deliberately crafted by an intelligent agency. As it happens, there are a number of good reasons to question prevailing accounts.
Animals marshal an array of stratagems to defend themselves in a world teeming with sharp-eyed, hungry predators. These defenses also help relieve the stress of constantly being on the lookout—a point seldom noted. Thanks to their defense mechanisms, many creatures go about their lives virtually unmolested thanks to built-in protections, some of which act in concert with what amount to flashing warning signs.
Here’s a partial listing of strategies, including a few singular cases:
• Many varieties of poisonous stings and bites. (Though used for securing prey these are often solely for protection.) Many insects are unpalatable as a result of concentrating toxic compounds from food plants in their own flesh. On the other hand, animals (such as frogs and newts) synthesize their own poisonous chemicals.
• A fearsome assortment of spines, spurs, bristles, and detachable quills. These can be poison-tipped or capable of causing potentially fatal infections.
• Diverse noxious, sticky, toxic, or just plain foul excretions and emissions are employed by many creatures throughout the animal kingdom. The chemical elements are sometimes altered versions of substances having other, often completely unrelated physiological roles.
• Along with their remarkable camouflage systems, cephalopods (squid, octopuses, and cuttlefish) deploy opaque “smoke screens” by expelling clouds of an inky substance.
• Many lizards and salamanders can voluntarily shed their tails, which then flail wildly, distracting the predator while the real prize escapes…and grows a new tail.
• Sea cucumbers (a soft-bodied mollusk) have a related trick: when threatened, they expel several internal organs. Some of the eviscerated tissue includes part of the sea cucumber’s respiratory system. This tubular material expands many fold, elongating and becoming sticky, sometimes disabling predators. The organs regenerate within days.
• Warning coloration: bright colors or stripes, often in combination with black stripes or against a black background, indicating toxicity or other dangerous defenses.
• The electric eel (actually, a type of fish) can deliver brief shocks of up to 850 volts.
• In addition to being well camouflaged, some species of the slow-moving horned lizards can spray blood from a special pore near the eyelid. In addition to the element of shock and surprise, their blood is reported to have a repellant effect.
• The bombardier beetle stores a mixture of hydroquinones and hydrogen peroxide in a special chamber near its anus. If threatened, the beetle empties the contents into another sealed chamber where the chemicals mix with a catalyst, triggering a violent reaction that raises the temperature of the mixture to near boiling. Resulting pressure forces the hot fluid through a turret-like nozzle that the beetle can aim in a chosen direction.
• Native to tropical waters, the diminutive boxer crab carries tiny sea anemones in each of its claws. The anemones’ stinging tentacles provide protection to the otherwise defenseless little crab (who also scrapes off food particles captured in the tentacles for its own benefit).
• The bizarre Malaysian exploding ant, suicide bomber of the insect world, belongs to a group of forest-dwelling ants that are often attacked by marauding weaver ants. Workers have enlarged mandibular glands running the length of their bodies. As a last resort in battle, worker ants violently contract their abdominal muscles which causes the poison-filled mandibular glands to rupture, spraying a sticky and corrosive fluid in all directions. This toxic glue can ensnare nearby attackers, immobilizing them.
Then there’s the passive protective device of cryptic coloration, which encompasses both camouflage and mimicry. Cryptic coloration comprises a number of distinct subcategories (often named after their discoverers). These include:
• Cryptism: The commonest form of camouflage, where an organism resembles a leaf, flower part, twig, rock, or the surface upon which it typically resides or rests. With ever increasing frequency, photographic images are appearing online showing exotic animals whose cryptism elicits gasps of amazement: walking-stick insects, caterpillars, katydids, mantises…geckos, toads, bizarre sea-horses such as the leafy sea dragon and other reef-dwelling fishes.
• Active camouflage: Through various physiological means, some animals can alter their coloration to match different backgrounds.
• Disruptive coloration: Patterns of bold spots or stripes that serve to break up an animal’s outline against a complex backdrop (as is the case with leopards and zebras). In combination with cryptic coloration, an animal virtually disappears against its background.
• Batesian mimicry: The “sheep in wolf’s clothing” trick, where a harmless animal resembles a toxic or dangerous one.
• Müllerian mimicry: Two or more unpalatable species come to resemble one another, reinforcing their warning coloration patterns.
• Automimicry: One part of an organism’s body resembles another part. (Snakes whose blunt-tipped tails resemble a head; butterflies and other insects whose hind-ends mimic heads.) If attacked, they might escape with non-fatal injuries.
• Wassmannian mimicry: The mimic lives alongside the model (generally one of the social insects—ants, bees, termites). Living within the model’s colony or nest, the mimic makes its presence tolerable by producing pheromones.
Astonishing examples of protective coloration elicit wonder and admiration and are frequently held up as proof of the existence of an intelligent creator. Some instances of camouflage and imitation come close to being beyond belief. Even after Darwin, leading scientists have confessed to doubting whether naturalistic explanations can account for some of the especially vexing cases. Nonetheless, the discovery of mimicry (as a biological phenomenon) by a Victorian-era naturalist was thought to be the first truly convincing demonstration of the powers of natural selection.
Henry Walter Bates, along with Alfred Russel Wallace, embarked on an expedition to Brazil in 1848. Bates and Wallace—only in their mid-twenties at the time—were both avid collectors of beetles and butterflies, a fashionable hobby in Victorian England. Each had been inspired by Darwin’s The Voyage of the Beagle, first published nine years earlier. Insect collectors (Darwin being one himself) were ideally suited to probe evolution’s mysteries, being particularly attuned to the variety and extreme diversity of the creatures they studied. The question of how such diversity arose was a much-discussed topic. Hoping to finally solve the problem of the origin of species, the two young men traveled up the Amazon River, together and then separately. Wallace, sick and exhausted, was forced to return to England in 1852. On the journey home, Wallace’s ship caught fire and sank—with all his specimens and notes. Bates remained abroad for seven more years. Having collected almost fifteen thousand animal species (eight thousand of them unknown to science) he arrived back in England, his body likewise ravaged by sickness and deprivation. Just months later Darwin’s Origin of Species was published. Bates became an enthusiastic supporter of Darwin’s new theory and the two became fast friends and life-long allies.
Bates’ most important contribution was the discovery of a previously unrecorded form of mimicry that now bears his name. In Brazil he noted many instances of one butterfly species that had taken on the colors and wing patterns of another. Typically, these markings were patches and stripes of vivid primary colors against a dark background (a key design theme among warning devices used by animals). After careful study, Bates found that one of the two—he termed it the model—was avoided by predators due to a diet of toxic plants while its mimic was safe to eat. Even more intriguing: during his travels, Bates repeatedly found distinct varieties of one of the unpalatable (model) species being impersonated by different varieties of the same mimic species. To further complicate matters, in some regions he found numbers of separate species—even day-flying moths—all sporting similar flashy wing patterns. And all along the way he came across instances of astonishing protective coloration. The sheer complexity and degree of sophistication of all these things captivated him.
Back in England, Bates promoted his findings as the clearest-yet demonstration of natural selection at work. He described his discoveries in Darwinian terms, explaining them in words similar to these: Through chance mutation, some varieties of butterflies acquire a purely fortuitous, crude resemblance to an unpalatable species. Over time, by way of a string of chance mutations, this resemblance increasingly grows more refined, with selection favoring the offspring of superior mimics. And ever since, books and articles have offered up the explanation proposed by Darwin and Bates as consummate illustrations of natural selection in action. But is the phenomenon as straightforward as this? Time and again, such matters have proven to be more complex than originally conceived. Are other influences at work here?
Much has been learned about butterfly wing patterns through laboratory rearing and cross-breeding experiments. In time it was found that colors and patterns on two-dimensional surfaces like insect wings are more readily altered by genetic changes than those on three-dimensional structures. In the 1920s and 30s, biologists determined that, in at least one major group, individual species’ markings are variations on a basic “ground plan” consisting of pattern elements—rows of stripes and spots confined to specific subregions bounded by wing-veins. An important observation was made: these subregions are modular. As such, they can evolve independently of other elements and do so without impediment. The established theory explaining butterfly mimicry is based on a two step model. Initially, mutations in regulatory genes responsible for wing coloration result in morphological changes that bestow a chance resemblance. The second step involves further small scale mutations which, when subjected to natural selection, progressively result in ever-closer resemblances. Modifications to wing patterns, being modular and subject to “point mutations” (changes in a single nucleotide base), occur readily. And often.
Thanks to explosive advances in evolutionary developmental biology (evo-devo), we now have a fairly detailed understanding of the genetic aspects of coloration and pattern development. Certain genes, previously identified in Drosophila and known to have multiple functions, were shown to be responsible for eye-spot formation as well. Location of such features is set by the ground plan. When, if, and for how long these genes are switched on determines whether any one locus develops into a simple spot or something more elaborate—for instance, one of those markings that bears an astonishing resemblance to a vertebrate eye, complete with a tiny silvery dot near its center to create the convincing illusion of a reflection on an eye’s glassy surface.
Many of these issues are far from settled, but investigators expect to make great strides in coming years. But conventional mechanistic approaches probably won’t unearth universal evolutionary pathways—developmental pathways that produce minor miracles such as wing markings on a species of tropical butterfly that replicate, with the realism of a trompe l’oeil painting, beaded raindrops. (As if this weren’t enough, there’s a thin line on the wing of this particular butterfly that is offset a bit where it passes beneath the sham water droplet, perfectly mimicking the visual effect of refraction such a spheroid “lens” would produce.)
Of all the graphic illustrations of the raw power of organic evolution, choice instances of crypsis are surely among the most astonishing in terms of subtlety, sheer inventiveness, and aesthetic appeal. Take the squid-like cuttlefish that alters its shape, color, skin texture and patterning—in an instant—to match virtually any backdrop (including, in one experiment, a fair rendition of a black-and-white checkerboard). One variety of octopus can ape—in both coloration and physical form—a stingray, flounder, or sea snake. Then there’s the diverse array of insects that are virtually invisible against the leaves, bark, or any substrate upon which they hide. And then there are those birds and mammals of northern latitudes that turn white in winter. [Note This critical adaptation has been independently invented by ptarmigan, weasels, foxes, wolves, hares, lemmings, and reindeer. (Note that the mammals represent four separate orders.) In light of this co-evolved adaptation’s remarkable utility, it’s somewhat surprising that the mechanisms behind the process haven’t yet been identified; all we know thus far is that there appears to be some connection with day length. If so, rampant and unchecked climate change taking place in arctic regions will surely have a grave effect on these creatures lives. While doubtful, some species may prove capable of adapting quickly.]
Darwinian theory has a ready answer for those who shake their head in wonder, marveling at how such things could ever come about: The occasional minor, random mutation—a frilly edged wing, a subtly different color, a seemingly inconsequential bump—provides a chance advantage. Which, if passed on to offspring, improves their odds of surviving and reproducing. Through time, by way of additional random alterations, these features change or are enhanced, becoming over time ever more realistic and thus effective. Like many others, in the case of cryptism my faith in the Darwinian account wavers. I find myself unmoved by the stock version; similarly, the explanations given for many forms of protective coloration lack empirical substance or even a feel of scientific authenticity. I make this subversive claim while bearing in mind the risk of falling prey to the fallacy of “arguing from personal incredulity.” Basing one’s line of reasoning on intuition and feelings of doubt isn’t a valid approach to scientific questions. But accepted scientific truth has been up-ended thanks to one person’s nagging misgivings—misgivings, yes, based on sheer intuition. Still, people with scientific backgrounds, aware of the specific issues, find the matter of cryptism a classic demonstration of Darwinism in action, not even remotely “mystifying.”
Speaking for myself: an experience that occurred when I was sixteen proved to be pivotal to a burgeoning awareness that certain natural phenomena seemed to defy rational, scientific explanation.
Hiking alone in a canyon near my home, I came across a sizeable gopher snake—at almost five feet long, the largest one I’d ever seen. (Regarding the emotional impact of encounters with wild animals: when serpents are involved, “size matters.”) The snake was hidden under an old board I’d just lifted and, with the sudden loss of cover, it speedily assumed a defensive posture. I felt a rush of adrenaline when it coiled, head reared and tongue flickering. Staring me down, the typically docile reptile became a rattlesnake. As it is, the gopher snake’s coloration and scale patterns bear a passing resemblance to that of their venomous cousins. But the startling transformation went way beyond simply taking on the overall appearance of a rattlesnake. The snake flattened and widened its head, the jaws flared out from the neck—a classic viper trait. The snake inflated its lungs, which markedly increased its girth. (Rattlers are conspicuously thick-bodied compared to most snakes.) The slender tail, held aloft, vibrated in a hazy blur—almost indistinguishable from the blur of vibrating rattles. Simultaneously, air forcefully expelled from the snake’s lungs, made a hissing noise that credibly reproduced that instantly recognizable buzzing sound. The imposter faced me squarely, slowly weaving its head from side to side. Anyone who has faced down an angry rattlesnake with adrenaline pumping through their veins will attest that it automatically triggers a compelling and instinctive fear; keeping one’s distance is an involuntary response. (Of course, being an adolescent male human, I felt compelled to locate a stick to wave in front of the snake’s face, provoking it to strike.) All in all, the entire display was a thrilling demonstration of plucky menace that left me thoroughly cowed. The memory is still vivid.
Later, thinking about what I’d witnessed, I was shocked to realize that along with its viper-like coloration and markings the snake had displayed a total of seven discrete behaviors mimicking actions exhibited by its venomous relatives: drawn up in a pile of sinuous coils…reared head held flat, jaws flared…tail borne vertically behind the coils, tip raised and vibrating in a blur…inflated body…exhaled air that sounded amazingly similar to that viscerally fear-inducing rattle…the spirited strikes. Eventually I learned that these copy-cat behaviors are common defensive responses (and that many gopher snakes die by human hands as a result of their too-clever subterfuge). But the thing that most amazed me was in realizing that these ploys had not been learned—they were wholly instinctive. Snakes don’t rear their young; no parental guidance imparted these skills. Nor is it likely that gopher snakes learn through observing and imitating their formidable relations. No: they’re born with this singular, instinctive talent for mimicry. How do they know? I still wonder.
Readers of literary fiction are by and large unaware that, prior to his celebrated writing career, the expatriate Russian novelist Vladamir Nabakov was well known among butterfly fanciers around the globe. Nabakov was for some years a curator of Lepidoptera (butterflies and moths) at the Harvard Museum of Comparative Zoology. A recognized expert in his field, Nabakov was well aware of contemporary neo-Darwinian thought when he included this memorable passage in the autobiographical work Speak, Memory:
The mysteries of mimicry had a special attraction for me. Its phenomena showed an artistic perfection usually associated with man-wrought things. Consider the imitation of oozing poison by bubblelike macules on a wing (complete with pseudo-refraction) or by glossy yellow knobs on a chrysalis (“Don’t eat me—I have already been squashed, sampled and rejected”)…. When a certain moth resembles a certain wasp in shape and color, it also walks and moves its antennae in a waspish, unmothlike manner. When a butterfly has to look like a leaf, not only are all the details of a leaf beautifully rendered but markings mimicking grub-bored holes are generously thrown in. “Natural selection,” in the Darwinian sense, could not explain the miraculous coincidence of imitative aspect and imitative behavior, nor could one appeal to the theory of “the struggle for life” when a protective device was carried to a point of mimetic subtlety, exuberance, and luxury far in excess of a predator’s power of appreciation.
Nabakov’s life-long fascination with mimicry and cryptic coloration roused in him a skepticism toward Darwinian explanations. His attitudes were shaped before modern evolutionary orthodoxy was settled, at a time when doubts of this kind were fairly common in certain fields. Later, Nabakov’s stance puzzled those who knew him as a credible scientist who was well aware that his contrarian views on natural selection were heretical. But Nabakov was far from alone in his skepticism—like many others, he questioned how something that so clearly showed signs of deliberate design could have resulted from slowly accumulating random mutations. (“The incredible artistic wit of mimetic disguise…seemed to have been invented by some waggish artist precisely for the intelligent eyes of man.”)
So it is that the bio-skeptic asks: How, through purely naturalistic means, does an animal contrive what amounts to an invisibility cloak? Despite claims to the contrary, this question has never been answered—it is routinely sidestepped. Here’s one example of how mimicry is “explained,” from Peter Forbes’ Dazzled and Deceived: Mimicry and Camouflage:
Very often we fall into circular arguments when we speculate on evolution because there is no purpose to it—no end in sight. We see that some organisms have survived, so we say that these must have been the fittest. And which are ‘the fittest’? Those which have survived. But in mimicry one creature has led and another has, through selection, copied it. The old problem of attributing to nature a goal when it has none dissolves in the face of mimicry because, although there is no purpose to the whole of it, for the mimicking species there is a goal: to copy the model. So we have an index of the success of evolution in producing the match. Similarly with the butterflies that mimic dead leaves. Success is demonstrable.
This is a striking but not atypical example of a phenomenon that was discussed in a previous essay: readers are warned of circular reasoning’s pitfalls, which the unwary often fall prey to. But here, Forbes stumbles into that very trap. How can we explain camouflage and mimicry from an evolutionary standpoint? Answer: Through the process of natural selection working on genes. How do we know that natural selection accounts for these features? Because, writes Forbes, “in mimicry one creature has led and another has, through selection, copied it.” Their success, as he asserts, “is demonstrable.” Classic circular reasoning. Christian de Duve, on mimicry: “Obviously, those traits did not develop for the purpose of protective covering. Neither were they copied. Mechanisms for such a phenomenon do not exist.”
Odd, that the fallacious reasoning so often glides by unnoticed…that the feature or phenomenon in question is never actually elucidated. Much progress has been made in describing mechanisms behind wing pattern evolution. They are well-supported and make perfect sense. But the real issue—how it is that all these astonishing instances of mimicry came to be—is ignored. The same goes for all forms of protective coloration. Nabakov didn’t live to see the genetics revolution. But even if he had, even if he’d known about point mutations and Hox genes, Nabakov would be asking questions like these: How, through gradualistic processes, have genes been modified to the extent that a butterfly so perfectly resembles a leaf that it includes gnawed-looking edges and patches that appear exactly like the decayed places on similar leaves? Why is blind natural selection prone to yielding such unbelievably artful details? What “codes” for a tiny, perfectly placed silver dot that imparts a sense of the moist reflectivity of an eye’s surface?
And here are a few more unanswered questions, seldom asked: Why, if protective coloration is so readily achieved by way of modular genetic mutation and selection, don’t more uncamouflaged species take advantage of such a beneficial adaptive trait? How is it that camouflage, being a result of random mutations that help individual organisms survive and reproduce, entire families, even orders (Mantidea—the mantises, for instance) are masters of the art across the board? Why don’t we see rudimentary, unfinished-looking instances of protective coloration that are clearly evolutionary “works in progress”? And this: or Batesian mimicry to “work,” the mimic has to be significantly less abundant than the model. (If mimics were as- or more-abundant than their models, predators sampling both species wouldn’t learn which to avoid.) How, then, are populations of Batesian mimics regulated to maintain relative scarcity—typically five percent or less of their model’s numbers? And this: as Nabakov pointed out, camouflage and mimicry need not be perfect in order to succeed; many crude but highly successful forms seen in nature bear this out. In fact, among the groups of butterflies Bates studied, mimics often bear only a crude resemblance to the model species. One final item: it would be of interest to learn how bugs that rely on careful positioning in order to turn into thorns or blend into the veiny surface of a leaf “know” to orient their bodies correctly (that is, to position themselves so that they vanish into thick tropical air as opposed to turning ninety degrees and turning into food). In many instances, these behaviors involve a specific way of positioning legs and antennae. These are simply inherited, instinctive behaviors, we are informed, like those of my gopher snake. No doubt this is true on one level but the fact remains that inherited behaviors—one of biology’s great mysteries—have thus far eluded scientific explanation.
Not only has my research failed to yield answers to these hard questions but thus far I have been unable to find askers. Meanwhile, innumerable instances of protective coloration have reached an evolutionary state of functional perfection and many of them achieved this state long, long ago. Such puzzles are little more than distraction in the face of deeper issues. Defense mechanisms and protective coloration are physical expressions of the survival imperative. They recapitulate in the clearest fashion what lengths LIFE will go to in order to help the living and further survival. LIFE doggedly finds a way and its solutions are something to behold. Protective coloration shows off nature’s signature flair, its tendency toward over-embellishment and whimsy. These, in (paradoxical) tandem with spareness and practicality. And there is that thing Nabakov, with his fine feel for the English language, called “exuberance.” In contrast, the theory of evolution by natural selection has no cause or means to even acknowledge an enigmatic richness and depth that is a non-material ingredient of all biological features. It allows only for randomness and great spans of time to work its faux-magic.
As with many of nature’s countenances, through their highly successful expressions of camouflage and mimicry plants and animals assume the guise of art. In the case of such “utilitarian” features, this seems an over-the-top extravagance—a needless addition of fringe and filigree. What some of us find a bit unnerving about LIFE’s aesthetic profligacy is a lingering suspicion that this particular form of natural beauty bears a veiled message. What we attempt to explain strictly in terms of function exists in nature as something more than simple practicality. Meanwhile, we’re left staring directly at the biological message while it remains concealed…hiding in plain sight.
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