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WHERE THE WOOD DUCK GOT ITS BEAUTY
Years ago, the writer and anthropologist Loren Eisley sat with a friend on the bank of a pond watching a wood duck. Turning to Eisley, the friend asked, “Do you really think the wood duck got this beautiful plumage by blind chance?” Out of a chaos of swirling stardust – atoms, electrons, protons, neutrons – can one fathom the creation of a wood duck without a creator? Eisley had no answer – but there is one now.
The wood duck knifed through the bare limbs of the hardwood forest at a reckless speed and hauled up, wings cupped in a vertical stall, on a thick branch of a dead elm. Behind it meteored its mate, twisting this way and that before landing beside the drake. For a minute, two minutes, they perched there, parallel to the limb, very un-duck-like. Then they edged their way out farther and suddenly dove off through the aerial tangle and out of sight. That they did not end up impaled by a branch or splattered on a tree trunk is one of the marvels of wood duck skill.
But there is another marvel about wood ducks, one that drives at the very heart of life and living things. Not that the marvel is unique to this species, just extreme, which makes the wood duck a symbol, a standard-bearer. Maybe other ducks, maybe all nature looks in awe at the wood duck, envious of its achievement, for the wood duck represents an example of the most, or the best, in gaudy beauty that nature can achieve.
For twenty-five years, every spring we hiked to the silver maple swamp at the back of our Ontario woods to ponder anew the imponderable, to work through the evidence once more. The spring woods is a good place for that, with life bursting anew, with hepaticas and trilliums poking up and the intricate songs of rubycrowned kinglets and winter wrens priming the breeze. But the trigger for this annual event was the wood ducks.
They would arrive before the leaves had budded, while the silver maples were decked out in tiny, crimson flowers. We would glimpse them after cautiously stalking along the edge of the swamp, our footsteps muffled by last year’s sodden leaves. They would be there, swimming alertly among the logs and stumps in the helter-skelter fashion that is uniquely theirs. The dark water down in the swamp would reflect their mirror image.
The male wood duck is the most brightly coloured of North American waterfowl, with red and white on its beak, a green cape over its head, cinnamon breast, and yellow flanks – a floating palette of colour. In the first Canadian bird book, Alexander Milton Ross described the “summer duck, or wood duck” as “without exception the most beautiful of all our ducks.” To be the most beautiful is an accomplishment because of other elegant challengers, such as the hooded merganser, with its white crest edged in black, its dark back, and russet flanks, or the canvasback, with its cinnamon head and red eye. But the wood duck, because it is overdressed even for a carnival, is the species that fairly shouts out, “How did I become so elegant, so richly coloured, so beautiful?”
The question nagged at us. Most people are curious about life’s complexity and beauty. Observing any being can prompt questions about how its attributes came to be. Take the veery, for example, a small, brown, nondescript thrush, the antithesis of splendid colouration. But have you ever heard its song, or a choir of them singing at dusk in the deep shadows of the forest? Many evenings in various Algonquin Park white pine cathedrals, while sitting beside a campfire or lying in the tent, we have listened to the veery ensemble, best of all choirs. We have recorded their songs, and when played back at half or quarter speed their liquid beauty and complexity is astounding. Some might say that if that song came about by chance, then so must have Beethoven’s violin concerto.
Then there is the Polyphemus moth, an insect of elegance, displaying tawny wings banded with grey, white, and touches of red, and sporting a single large “eye” on each hind-wing. The “eye” is a perfect mimic of a large vertebrate eye, complete with a fake pupil, but constructed out of wing scales instead of the stuff of a functional eye. What about the splendour of a pink, deep-throated calypso orchid, intricately designed for insect pollination? Or the vertebrate eye, a marvel of engineering? Or the human brain? It’s little wonder that people recoil at the thought that living things, including us, have come about by chance.
Yet, hold on. “Chance” is a loaded word, as any Mississippi gambler knows. Could it be that the deck of life is stacked, the dice loaded, the game rigged? Is it possible that rules and regulations exist, to be adhered to or broken? Might winners be rewarded, transgressors cut down? Maybe a wood duck’s bright plumage was “in the cards” all along.
Natural selection exerts the most immediate and severe curb on chance, the picking and choosing by the environment of the individuals that are best fit, or, more accurately, the weeding out of the less fit. It operates with just two requirements: replication and variation. The former is met by the production of offspring, the latter by their physical differences. Those individuals whose differences confer some adaptive advantage, be it environmental fitness, competitiveness, hardiness, or longevity, will invariably leave more offspring. Populations will become dominated by them. Evolution – sequential change – will have occurred. It is as intuitive and simple as that. It has been verified experimentally in many ways, such as in a long history of crop and livestock improvement.
How natural selection has led to the wood duck’s plumage, however, involves a special twist. In spring, wood ducks spread out across the southeastern, central, and western sectors of North America, where they occupy small ponds and wooded swamps. At that time, wood duck drakes are decked out in full splendour, as are all ducks. After breeding they enter a post-nuptial moult, becoming drab brown and staying that way through late summer and early fall. So do most songbirds. However, a telling difference between ducks and songbirds happens next. In late fall, ducks moult back into their bright plumage, while most songbirds wait until spring. Predictably, display and pair bonding begins in both groups as soon as they are dressed appropriately for the occasion. This difference in timing illustrates that the selection pressure that drives bright plumage is mating, with its dual requirements of attracting a female and out-competing other males.
In male vertebrates, a great variety of anatomical features help play this role: crests; plumes; fanned tails; brightly coloured eyes, beaks, legs, and feet; horns and antlers; and large body size – all developed to attract female attention. So pervasive and obvious is selection for mating purposes that Charles Darwin termed it “sexual selection,” differentiating it from natural selection, which he related more closely to survival. He defined sexual selection as “the advantage which certain individuals have over others of the same sex and species solely in respect to reproduction.” Sexual selection, then, a special type of natural selection, has been the dominant force driving the plumage characteristics of wood ducks.
The significance of sexual selection in creating display features in animals does not mean that natural selection is less functional. Heavy persecution has illustrated natural selection at work, too. For instance, the selective effects of severe trophy hunting has caused shrinkage in both horn and body sizes in several species, such as bighorn sheep in Alberta. Wood ducks also have been heavily hunted, so much so that further shooting was banned between 1918 and 1941 and limited for years after that. However, unlike mammals with horns, hunters do not select which wood duck to blast on the basis of its appearance. If they did, then selection would have taken place and wood ducks would have lost some of their beauty, because the price of being more beautiful than other wood ducks would have been an earlier death with fewer or no offspring.
Conservation measures, primarily limitations on hunting, have brought wood ducks back. In my (John) student years they were still recovering, and part of my job for the Metro Toronto Conservation Authority was to survey their breeding success at nesting boxes provided to owners of private ponds. After a lot of ladder climbing and more than a few falls, it turned out that most of the boxes were unoccupied. Then, one autumn evening twenty years later, as we traversed a dike out in the broad Long Point marsh on the north shore of Lake Erie, wood ducks seemed to fill the sky. They were on migration, congregating at the mouth of this land-funnel that extends out into the lake. We watched flock after restless flock skitter across the orange sky and dip into the marsh for the night.
Today, the estimated fall population of wood ducks in North America is between 2 and 4 million after the hunting season, which still slices out more than 1 million and is the principal cause of death. However, the wood duck population seems to be reasonably secure.
Thus, natural and sexual selection provide the immediate answer to the question of where the wood duck got its beauty. Selection has curtailed chance by drawing only certain cards from the deck that suit its purpose – to leave more offspring. Today, as Darwinian natural selection receives ongoing and even increasing attention from biologists, especially with the advent of new techniques in genetics, its basic tenets, and power, are repeatedly reconfirmed.
Chance is more closely associated with genes than with natural selection. Genetic variety comes first, then nature selects from it. But where did the genes originate that dressed the wood duck that way? Again, the deck is stacked, but with greater cunning, a more subtle sleight-of-hand.
Here we enter the laboratory world of the geneticist working, ironically, with both the very basis of life and at the same time only its abstraction. To correct for it, we gave a photograph of a wolf to our geneticist partners to hang on the wall so they could look up from their microscopes now and then and remind themselves of what they were studying.
Geneticists have made remarkable gains in explaining how genes work. But the field is relatively new, only some hundred years old, and misinterpretations happen. The pioneering work of Gregor Mendel with variously coloured peas led to the idea of simple inheritance – one gene equals one biological trait. However, through mapping of the human genome and similar projects, it turns out that most genes are linked, reducing chance, as if some cards in the genetic deck were stuck together. Other genes simultaneously control several features of an organism, or form complexes, or play regulatory roles by turning certain genes on or off. Geneticists today puzzle, for example, over phenomena such as “hox genes,” which are clusters of genes that express themselves as an overarching group during the development of an organism.
Interacting genes raise the possibility that each characteristic of a wood duck – its red eye, its green helmet – did not come about independently. Interacting genes could have acted to cause the wood duck to suit up in its particular way, without hypothesizing the chance appearance of many individual and unrelated genetic events, just as we do not buy our clothes thread by thread, but as a jacket, blouse, or pants.
The seamy biochemical world of DNA is a complex environment of interacting atoms and molecules that respond to the dictates of electrons, protons, neutrons, and sub-atomic particles. Some interactions allow chemical bonding, others result in rejection. But despite this complexity, two primary patterns emerge: recombination of existing genes, and mutation that forms new genes. Recombination, the more important of the two in providing genetic variation, is the shuffling of existing genes from generation to generation. Chance dictates these rearrangements but it is curbed by the limitation of what is there. By analogy, there are only fifty-two cards in the deck, not some larger number, and each card has a specific face value. These impose limits. However, in the deck of genes, now and then a chance mutation will show up, a new card shuffled in.
The genetic deck would be stacked even more if the French biologist Jean-Baptiste Lamarck, who advanced the infamous theory of the “inheritance of acquired characteristics,” had been right. For decades he has been set up in the history of science as Darwin’s stooge. However, he actually foresaw evolution, which in his day was called “transmutation,” meaning one form changing into another. Lamarck argued against the established theory of the immutability of species. In a way, he provided a starting point for Darwin, who then had only to get the central mechanism – natural selection – right.
Lamarck’s mechanism, the “inheritance of acquired characteristics,” has long been decried as a mistake. An example given in both old and new genetics textbooks is of a blacksmith who builds up big biceps from swinging a hammer. He will not give birth to children with big biceps, as Lamarck supposed. The father’s occupation cannot influence the genes he passes to his offspring. A giraffe that stretches its neck to reach higher up in acacia trees will not produce young with longer necks as a result. Too bad. Many of the marvellous adaptations of living things would be considerably more plausible if such a direct feedback from an environmental need to an anatomical structure were true.
But wait. Lamarck’s theory has life in it yet. In 2000 an article appeared in the prestigious journal Science with the title “Was Lamarck Just a Little Bit Right?” The article detailed ongoing research that explains how the environment can call various genes into action, or silence them, with down-the-gene-line inheritable effects. (This new field of discovery is explored in Chapter 2.) However, at this point in the story, it is enough to recognize that genetic chance is curbed by most genes hanging out in gangs and acting in coordinated ways, and by the deep physics of the lockstep molecular waltz.
As well as natural selection and genetics, helping to explain the wonder of the wood duck is time, another way that chance is reined in. For change to happen and eventually build intricate biological things – a wood duck’s plumage, a veery’s song, a vertebrate eye, the complex physiology of our own bodies – takes time, deep time, immense caverns of time. Darwin realized that and went to his grave puzzled by how evolution could have proceeded from unicellular organisms to complex animals in just 100 million years, that being the accepted age of the planet in his day.
The time involved in biological evolution is unfathomable. With enough time, with each reshuffling of the genetic deck generation after generation, the chances of a seemingly impossible anatomical structure emerging increase. Impossible may become improbable, then only unlikely, then, reshuffled over and over again, may become possible, even probable – and then the structure appears. Play till you win. But the process of winning through natural selection is an incremental thing, like a gambler amassing his earnings gradually, hand after hand. Each slight improvement that is advantageous is retained and built upon. This key point in understanding evolution through natural selection explains why the improbable construction of wonderful things, like the vertebrate eye, or the wood duck’s plumage, is not an unfathomable engineering feat. Each was, instead, the consequence of tiny, incremental improvements over long reaches of time.
Glaciers left most of the northern hemisphere 10,000 years ago, the first human showed up 2 million years ago (depending on where you draw the Australopithecus-Hominid boundary), the final rise of the Rocky Mountains happened 5 million years ago, dinosaurs died out 65 million years ago, the first deciduous trees appeared 120 million years ago, life left the seas and crawled up onto land 440 million years ago, the first life on Earth emerged between 3.5 and 4 billion years ago, our planet formed 4.5 billion years ago, the universe originated 13 to 15 billion years ago. Few people have these dates memorized, maybe because we cannot comprehend such vast stretches of time. In the vacuum caused by this lack of comprehension lies the difficulty in accepting that, with enough time, remarkable things are possible.
Time has worked on the lineage of ducks, just as it has on all biological lineages. The average length of time for a new species of bird to emerge has been estimated as between 3.3 and 5.5 million years. Although recognizable change can happen in just a few years, the rapid evolution of any species must be accompanied by several conditions – such as quick, almost complete population turnover and genetic isolation – and is an exception, not the rule. No wonder species look immutable, just like the position of the continents. The world, however, is not how it seems. Things change.
The closest living relative of the wood duck is the mandarin duck of Asia, India, and southern Russia. Male mandarins are brilliantly coloured in ways that show their relationship with wood ducks. They too have white shoulder crescents and yellow flanks, but they have large white patches on their heads. Females of the two species are almost indistinguishable. Wood ducks and mandarin ducks are the only two species in their genus, Aix, and obviously had a common ancestor that has been lost in time.
After the mandarin duck, the wood duck’s closest living relative, based on admittedly incomplete evidence, appears to be the hooded merganser, with which it shares a few characteristics, such as relatively small body size, a crest, a preference for small ponds and semi-wooded areas, and the habit of nesting in tree cavities. Genes program behaviour, too.
How long ago the split occurred that separated genus Aix from an ancestral line is unclear, but a proposed date for an earlier split between ducks and geese/swans based on fossil evidence is 25 million years ago. By 15 million years ago, many genera of modern-day ducks were present. Genus Aix likely appeared somewhere at the earlier end of this range of dates. Somewhere back then, the wood duck got its beauty.
Back then, the world was different. It was hotter. Even though many species of mammals were similar to those of today, wood ducks would also have run across four-tusked gomphotheres and short-faced rhinoceroses wallowing in the mud at pond edges on the central plains. Then, in the Pleistocene Epoch, over the past 2 million years, they witnessed sabre-toothed cats stalking mammoths, and gigantic ground sloths reaching high up into trees to browse. Wood ducks persisted despite the comings and goings of glaciers, the kaleidoscope of environmental change, and the appearance of humans. Wood ducks can boast of a robust, timetested design.
To recap: natural selection, genetic variation, and time are the three necessary ingredients for the evolution of the beauty and complexity of life, a fact we have known for more than half a century. Yet, each spring, as we looked at the year’s first wood ducks in the silver maple swamp, we wondered if that is all there is to it. And now it seems that there is another ingredient at play. Possibly, we are on the edge of a new and expanded view of life. Natural selection, genetic variation, and time may have an accomplice. Like Ali Baba, we are just now opening the door and glimpsing a large and beautiful chamber within, one that will take years to explore. The sign on the door reads “Order for free.”
A hint of the existence of this other ingredient was provided in 1949 by the American paleontologist George Gaylord Simpson in his seminal book The Meaning of Evolution. The first two-thirds of the book are devoted to the overwhelming evidence for evolution. Simpson’s great accomplishment was to work out relationships among fossil mammals across the 200 million years of their existence. His even greater accomplishment, however, is found in the last part of the book. In Simpson’s day, as today, evolutionary understanding was founded on what is known as the Modern Synthesis that married Darwinian natural selection with genetics. But, having explored how evolution happens, Simpson went on to ask: Where, if anywhere, is it going? In asking this question, he laid the foundation for the fourth ingredient of evolution.
Simpson rejected “finalism,” for example, which held that life is progressing towards some utopian state, towards heaven on Earth. Fossil evidence showing the prevalence of extinction and blind alleys refutes that. As well, he rejected an alternative viewpoint, called “vitalism,” which postulates the existence of a unique life force, because none has ever been found. Instead, Simpson concluded that what separates life from non-living things is organization alone. Both are comprised of the same elements found on the Periodic Table that adorns the walls of chemistry laboratories the world over. Involved in both, too, are the basic forces or laws of physics. In living things, however, the elements are simply put together differently, in a self-replicating and metabolizing way – self-organized rather than directed by an unseen force.
Today, evidence is mounting to support Simpson’s conclusion that spontaneous order or pattern in nature is generated by interacting parts operating together to form systems, whether those parts be molecules in rock, sand, clouds, a chemical flask, or living things. For example, an automobile engine is a system that operates by virtue of interacting parts. So is an individual organism, a population, an ecosystem, a solar system.
If order does emerge, fuelled from the sun, where does that order come from? What does it mean for evolution and life? For some years, to introduce students to these questions, I took two objects to my third-year ecology class for what I called the annual “shell game.” One was a porphyry olive shell, which is a ten-centimetre-long marine member of the snail group. It is coloured off-white with an intricate and beautiful pattern of spiderweb-thin, brown symmetrical scales. We had picked it up on a seashore in New Zealand. The other object was a geode cut in half to reveal its inner crystalline core. That had come from Arizona desert country, a remnant of an ancient volcanic explosion.
I held up the shell first, with the question: “What is the origin of its beautiful and intricate pattern?” Always someone would answer, “natural selection,” an understandable response, because that part of the course dealt with natural selection. Discussion would follow about protective colouration on a shallow sea floor where light dappled in, or similar adaptation to one thing or another. Then, I brought out the geode, and immediately obvious was that natural selection did not apply. It was an inanimate object. But it also displayed order and beauty. Did that come about by chance?
Pattern formation is well known in chemistry and physics. The interacting subunits are inanimate objects such as grains of sand or chemical reactants. Pattern, such as on the surface of boiling water or oil, or the sand ripples on a beach, is created through interactions based solely on physical laws. Pennsylvania biologist Scott Camazine, senior author of a book on self-organization, explains, “The molecules of oil obey physical laws related to surface tension, viscosity, and other forces governing the motion of molecules in a heated fluid. Likewise, when wind blows over a uniform expanse of sand a pattern of regularly spaced ridges is formed through a set of forces attributable to gravity and wind acting on the sand particles.” Similarly, the ordered, crystalline structure of a geode is founded on physical laws such as gravity and the forces that operate in atoms that bond silica and oxygen into molecules of silicon dioxide and associated minerals in a certain, structural way.
What about the shell? Biological systems must obey the same physical laws. All matter is so bound. Why can’t whatever created order in the geode also have worked on the shell? Instead of attributing the shell’s pattern solely to natural selection, more likely natural selection has operated later, on pre-existing order brought about by the nature of complex systems – physical, chemical, or biological.
The proponents of spontaneous order, like Stuart Kauffman and Brian Goodman, have thought a lot about biology, too. When asked where on a scale of one to ten they would rank natural selection in its importance in creating biological order, with ten being highest, Goodman responded, “Close to one.” That is revolutionary! Most biologists would score it up around eight or nine, or even ten. The view of people espousing spontaneous order is that natural selection works on pre-existing order. Natural selection, then, explains how organisms fit their environment, but is not sufficient by itself to explain the existence of order.
Darwin himself sensed a basic, pre-existing order. Daniel Dennett, in his book Darwin’s Dangerous Idea, attributes to Darwin the words: Give me order and time, and I will give you design. Let me start with regularity – the mere purposeless, mindless, pointless regularity of physics – and I will show you a process that eventually will yield products that exhibit not just regularity but purposive design. Order, then, is mere pattern. Design is pattern put to a purpose. Natural selection achieves that purpose.
For self-organization to emerge without the benefit of external blueprint, plan, or leader, there must be some rules. Discovering rules has been at the heart of the advances in understanding selforganization, because with a computer, it is reasonably easy (for the computer specialist) to simulate their effect. Start with unorganized dots or blips or any symbol put up on the screen. Establish a set of rules that describe when the symbol will be turned on or off by virtue of what its neighbours are doing. Let the program repeat itself over and over, so that it mimics biological generations, and pattern emerges, to repeat itself indefinitely.
Imagine our surprise and satisfaction one day in finding a picture of a porphyry olive shell in Camazine’s book describing self-organization. He discusses the work of a biologist named David Lindsay, who was able to simulate the exact pattern of that shell on a computer by establishing a set of random points and imposing on them just a few simple rules. The rules were simple instructions that he programmed about the frequencies of different combinations of vertical and diagonal lines that occurred in the shell pattern.
Now, envision similar simple structural rules being applied to the DNA-molecular gel in a reproducing cell. Pattern will emerge. Complex rules may not be necessary. As described by Camazine, “The richness of structures observed in nature does not require a comparable richness in the genome but can arise from the repeated application of simple rules by large numbers of subunits.”
Where do the rules come from? Much more remains to be discovered, but natural selection plays an obvious part. If rules do not work for a species, natural selection will purge them from the population. If rules work, they will persist. Camazine says, “Natural selection tunes the parameters of living systems to avoid chaos. In most situations, it would probably be grossly maladaptive for a living system to exhibit chaotic, disorganized pattern.”
Such a view of evolution, with a part played by inherent order worked on by natural selection, is comforting; any mechanism that reduces total blind chance in evolution is comforting. However, the validity of this concept comes not from the comfort it provides, but from objective analysis and synthesis – in that fundamental way, science departs from dogma. Enough evidence has accumulated to make the idea of spontaneous order in biological systems convincing.
So we return to the wood duck’s plumage, an ordered product of greatly whittled-down chance. The marvellous adaptations of living things come about partially from pre-existing order operating in or on genetic systems with rules established, in part, by physical laws and, in part, by natural selection. In addition, natural selection operates on individual traits after they are formed. That dual role for natural selection justifies a higher score than the “one” given by the proponents of spontaneous order for its contribution to order and design, raising it to at least five or six, maybe higher.
Add time, generation-by-generation adjustment, and occasional mutations. Add more time. Bright male plumage is favoured by females in their choice of a mate, which provides positive feedback to go on adjusting incrementally in that direction, possibly with the help of some linked or interacting genes creeping in. And behold, a drake wood duck! Based on what we know today, that, roughly, is how it got its beauty.
Undoubtedly, there is more to it. If ours is a complete explanation, then science is at an end. Instead, in every field, science progresses. One discovery leads to another, the questions becoming more fundamental all the time. That is what makes science exciting.
We eventually sold our home in southern Ontario and moved to British Columbia, so we can no longer walk to the silver maple swamp and ponder the secrets of wood ducks. We still visit our cabin near Algonquin Park, however, nestled beside a beaver pond studded with standing and dead trees – just the place for wood ducks. They nest there, and each spring morning above the raucous chorus of spring peepers and gray tree frogs we can discern their high, squeal-like calls. We used to canoe out to them for a better view, but our pond, like all beaver ponds with enough time, has partially drained. Still, there is sufficient water for at least one pair of wood ducks. When we return next spring for our annual visit, we will be looking for them.
From the Hardcover edition.