Pete Dunne, in his wonderfully didactic Essential Field Guide Companion, classifies the Brown-headed and Pygmy nuthatches as the “pack nuthatches.” I like it! For starters, I like how “pack nuthatch” conveys—shall we say?—essential information about the flocking behavior of these peripatetic pixies of the pinewoods. I also like how “pack nuthatch” hints at something about nuthatch evolution; I like how the name implies that the Brown-headed and Pygmy nuthatches are each other’s closest relatives. They’re the only “pack nuthatches.” Other nuthatches, in Dunne’s formulation, get other monikers.
It is plausible, I hope you will agree with me, that the Brown-headed and Pygmy nuthatches are what ornithologists refer to as “sister species.” That means they evolved from a shared, or “common,” ancestor—one not shared by any other extant bird species. If ornithologists had been around to classify that common ancestor, they would have given it a name. Maybe they would have called that bird—why not?—the capital-P Pack Nuthatch.
Today, of course, the Brown-headed and Pygmy nuthatches are classified as two separate species. Many thousands of years ago, in the scenario outlined in the previous paragraph, they—or, more properly, their ancestors—were one single species. The process of going from one species to two species was gradual. It’s not as if the Pack Nuthatch suddenly split into the Brown-headed and Pygmy nuthatches at say, 9:00 a.m. G.M.T. on Tuesday, October 23rd, 4004 B.C. Rather, there was some period—lasting perhaps hundreds or thousands of years—during which the (properly hyphenated, lower-case) pack-nuthatches were neither one species nor two species. (Left: Pygmy Nuthatch by © Bill Schmoker.)
I think most of us will have had no problem with the preceding. We understand that “speciation”—the process by which species come into existence—usually requires a long time and tends to be gradual. We understand that you don’t just flip a switch at some point in geological time, and declare that species A has instantaneously been transformed into species A’ and A”.
Or do we? Do we really accept that that’s how evolution works?
Consider now the example of the eastern and western populations of the Red-shouldered Hawk. It’s certainly plausible that these two populations arose from a common ancestor, some undifferentiated (“monotypic”) Red-shouldered Hawk. But their breeding populations are completely isolated at the present time; and with continued isolation of their breeding populations, they might well evolve into two separate species. Gazing into our crystal ball, we’ll say that, thousands of years from now, those two separate species will have been christened the Swamp Buzzard and the California Buzzard, respectively. (Right: California Red-Shouldered Hawk by © Bill Schmoker.)
That’s all well and good. A single species, the Red-shouldered Hawk, thousands of years ago. And two species, the Swamp and California buzzards, at some point thousands of years in the future.
But what about right now, in the second decade of the 21st century? Are these birds still one species? Or have they already become two species?
Or are they neither one species nor two species?
Think back to Pete Dunne’s “pack nuthatches.” At some point in their evolutionary past, we all agree, those nuthatches were neither one species nor two. Rather, they were in transit, if you will, from being one species to being two species. They were in the process of speciation.
Speciation is an ongoing process. It happened eons ago, and it’s still happening today.
And that brings me to what I consider to be one of the great ironies of modern thought. Many of us snigger at Creationists for imagining that all species came into being, perfectly formed, in an instant, at some point in the not-so-distant past. And yet many of us—we non-Creationists—do the exact same thing in our view of “species” at the present time. We demand that a population of organisms be this species, or that species, or these two species, or those two species, or three species, or four species… Like the Creationists, we cherish the idea of the fixity of species. The Creationists say that species were fixed at the moment of Creation. We say they’re fixed right now.
We say that the Red-shouldered Hawk is either one tick on our checklists or two ticks on our checklists. Conversely, we reject that the Red-shouldered Hawk could be both one tick and two ticks at the exact same time. And yet every credible analysis of “Darwin’s dangerous idea” demands that very interpretation.
Speaking of Darwin…
Toward the beginning of On the Origin of Species, Charles Darwin launches an attack on the proposition that it is meaningful to say that a population of organisms is or isn’t such-and-such a species. In Chapter 2 (“Variation Under Nature”) of Origin, Darwin writes:
“It must be admitted that many forms, considered by highly competent judges as varieties, have so perfectly the character of species that they are ranked by other highly competent judges as good and true species. But to discuss whether they are rightly called species or varieties, before any definition of these terms has been generally accepted, is vainly to beat the air.”
Then a full-on shot across the bow of ancient thinking about species:
“Certainly no clear line of demarcation has as yet been drawn between species and subspecies—that is, the forms which in the opinion of some naturalists come very near to, but do not quite arrive at the rank of species; or, again, between subspecies and well-marked varieties, or between lesser varieties and individual differences. These differences blend into each other in an insensible series; and a series impresses the mind with the idea of an actual passage.”
And a few paragraphs down:
“From these remarks it will be seen that I look at the term species, as one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other, and that it does not essentially differ from the term variety, which is given to less distinct and more fluctuating forms.”
From this point forward in Origin, Darwin sets about the task of dismantling the old idea of the fixity of species. In chapter after chapter, Darwin adduces example upon example of the fluidity of evolution by means of natural selection. Darwin’s Victorian prose can be a bit of a slog for the modern reader, increasingly accustomed to the conveyance of every idea via the medium of the 140-character “tweet.” But those subsequent chapters are worth the slog: Darwin marshals massive evidence in support of the view that evolution has been happening for very long periods of time, and, furthermore, that evolution is still happening.
And then we come to the final chapter of On the Origin of Species. Chapter 14 (“Recapitulation and Conclusion”) is a tour de force, one of the greatest scientific treatises of all time. Darwin seems to give it his all in Chapter 14. And in Chapter 14, Darwin unleashes his final, devastating assault on the idea that populations of organisms must be attributed to this species or that species.
“No one can draw any clear distinction between individual differences and slight varieties,” he writes, “or between more plainly marked varieties and subspecies, and species.”
“On the view that species are only strongly marked and permanent varieties, and that each species first existed as a variety, we can see why it is that no line of demarcation can be drawn between species, commonly supposed to have been produced by special acts of creation, and varieties which are acknowledged to have been produced by secondary laws.”
“When the views entertained in this volume on the origin of species, or when analogous views are generally admitted, we can dimly foresee that there will be a considerable revolution in natural history. Systematists will be able to pursue their labors as at present; but they will not be incessantly haunted by the shadowy doubt whether this or that form be in essence a species.”
For many people, Darwin lets on, “This may not be a cheering prospect.”
True enough, “But we shall at least be freed from the vain search for the undiscovered and undiscoverable essence of the term species,” Darwin concludes.
All of which brings me around now to the matter of the Austrian composer Arnold Schoenberg.
If you could stick with me through this next section, I would be most grateful. I accept that it might seem odd that I’m dragging in a composer who was born more than 100 years ago. But I’m going somewhere with this, honest. And, before too long, I’ll be talking about The Sibley Guide. We’ll be back on familiar ground soon enough.
Arnold Schoenberg is perhaps the most notorious “classical music” composer of all time. His scandalous “achievement” was to discard what had generally come to be regarded as Western tonality—a way of making music that characterizes the oeuvres of everyone from Franz Schubert and Felix Mendelssohn to Paul McCartney and Michael Jackson.
If you look at a sheet of music—whether it’s “Let It Be” or “Der Erlkönig”—the very first thing you’ll see is some indication as to key signature. This key signature is a system for ordering the relationships among the various notes within a particular work of music. In conventional, or “classical,” Western tonality, a piece of music has to be in a certain key. McCartney’s “Let It Be” is in the key of C major, for example, and Schubert’s “Der Erlkönig” is in the key of E minor. It wouldn’t make sense, according to Western tonality, to say that a piece were simultaneously in C major and E minor. Even weirder would be to say that a piece weren’t in any key at all.
Enter Arnold Schoenberg. Like many composers of his generation, he pushed the limits of conventional tonality. In doing so, Schoenberg and his contemporaries were heeding the timeless artistic impulse to push the limits of form and style. Wolfgang Amadeus Mozart, that great paragon of classical music, delighted in the expression of such impulses. His “Dissonance” Quartet starts out in a manner so as to obscure the key signature of the work; but after a short tease, the work gallops off in that most conventional of key signatures, C major.
Schoenberg, however, took it a step further. A big step further. When it comes to pushing the limits of Western tonality, Arnold Schoenberg was the Neil Armstrong of composers. In the last movement of the second string quartet, composed in 1908, Schoenberg took the giant leap of composing music with no key signature at all.
It would be an understatement to say that Schoenberg’s atonal music was controversial. Indeed, Schoenberg’s music was—and still is—widely hated. Why? Why is that?
Well, one reason—and it’s a big reason—has to do with personal taste. To be blunt about it, many people just don’t like the sound of Schoenberg’s atonal music. That’s fine. Some people don’t like the sound of Mozart. Some people don’t like the sound of McCartney. Some people don’t like the sound of John Coltrane. Some people don’t like the sound of Ravi Shankar. That’s all well and good. It’s personal preference—no more, no less—and I ain’t goin’ there.
But there’s another reason, and this one is going to bring us back to the matter of “pack nuthatches” and Red-shouldered Hawks. The other reason is that Schoenberg’s music—even to a great many folks who have never heard it!—represents something sinister. The objection to Schoenberg is more ideological than aesthetic. In this view, the music of Schoenberg is destructive and degenerate. According to this view, Schoenberg took something wonderful—the great “classical” tradition of Mozart, Schubert, and others—and degraded it. The old way was ordered and beautiful; the new way was chaotic and ugly.
Enter The Sibley Guide.
In my opinion, The Sibley Guide is the greatest field guide ever.
I think a lot of people would agree with that assessment of mine. From time to time, though, I do hear a particular gripe about The Sibley Guide. As critics note, The Sibley Guide, in its very extensive treatment of geographic variation in birds, abandons the age-old practice of assigning “trinomials” to regionally distinct populations. Other guides refer to the occidentalis and wymani subspecies of the Western Gull, but David Sibley simply calls them “northern” and “southern.” Willow Flycatchers get a whole bunch of names (adastus, brewsteri, campestris, extimus, traillii…) in other guides, but they’re simply “western” and “eastern” in The Sibley Guide. And in Sibley’s account of the Dark-eyed Junco, even though it shows thirty-one individuals spread across three large pages, there is nowhere to be found mention of a trinomial.
I’ll come right out and say that, unlike many of my birding friends, I strongly applaud Sibley’s decision to forego the use of trinomials.
But I’m getting ahead of myself.
First things first. Why? Why did Sibley do that? Why are trinomial names absent from The Sibley Guide?
Well, a great start would be to read Sibley’s own words. Check out his essay, “In Defense of Listing, and Subspecies, but Not Listing Subspecies,” which appeared in the February 2004 issue of Birding.
In the meantime, here are three thoughts of my own:
1. I favor Sibley’s decision because it promotes knowledge of and understanding about what we really see in nature. I think it’s realistic for experienced observers to distinguish between generalized and somewhat fuzzy groupings of “western” vs. “eastern” Willow Flycatchers. Many—although certainly not all—of these birds can be said to possess a suite of traits that correspond to one regional grouping or the other.
2. Conversely, when we start to get into campestris Willow Flycatchers vs. traillii Willow Flycatchers, we’re courting disaster. Well, that’s a bit strong. But I think we can certainly say that we’re flirting with fantasy. According to part 1 of Peter Pyle’s magisterial Identification Guide, any differences between campestris and traillii may, in fact, be fantasy. They may simply be two different names (“synonymns”) for the same population. (Right: Willow Flycatcher by © Bill Schmoker.)
3. So why all the grousing about no trinomials in The Sibley Guide? I think it’s because The Sibley Guide is analogous, in some sense, to Arnold Schoenberg’s second string quartet. Just as many people would say that a work of music has to have a key signature, so many people believe that a bird population has to be attributable to a certain taxon.
I need to be crystal clear about something. I am not saying that birders want every single bird to be attributable to one taxon or another. We all know about Thayer’s Gulls. We know that not every individual candidate Thayer’s Gull can be definitively called by that name. That’s not what I’m talking about. Rather, I’m talking about the entire population. I believe that many birders believe that the Thayer’s Gull ought to be either its own species or “just” a subspecies. But that’s missing the point, I believe. The fundamental debate, as I see it, is not whether the Thayer’s Gull is or isn’t a full species. Rather, the debate is about something deeper than that.
Think back now to the example of the Red-shouldered Hawk. The question is not whether the California population is a full species (I called it the “California Buzzard”) or “just” a subspecies of the Red-shouldered Hawk. No, the fundamental question, as I see it, is whether the Red-shouldered Hawk has to be either one species or two species (or more). I don’t think it has to be one or two. I believe that that view of mine comes from a faithful reading of On the Origin of Species. And I believe that that view is an exciting—and, ultimately, deeply liberating—consequence of what I consider to be one of the most useful and revolutionary features of The Sibley Guide.
We’ve arrived now, if provisionally and tenuously so, at a new sort of avian taxonomy—one without names. To be sure, it’s just a start. The Sibley Guide, of course, makes use of scientific names, or “Latin binomials,” for those taxa which enjoy full-species rank. Even though Sibley discards elegans as the trinomial for the California population of the Red-shouldered Hawk, he most assuredly does employ Buteo lineatus for the species as a whole.
So it’s just a start.
And, truth be told, Schoenberg’s second string quartet was just a start. Only the last movement of the work is atonal. And even that last movement ends on a major-key tonal chord. But he’d let the genie out of the bottle. There was no stopping what was to come—the full-on atonality of what has come to be known as twelve-tone serialism.
Now hang on a second! As I noted earlier, lots of people hate Schoenberg’s music and legacy. And in some sense, Schoenberg has to be rated a failure. Although there are certainly exceptions, most “classical” composers have not followed in Schoenberg’s footsteps. Most of the “classical” music of the 20th century is not atonal. Meanwhile, there are all the other musicians who are generally said to work outside the “classical” milieu: Paul McCartney and Michael Jackson, John Coltrane and Ravi Shankar, and many others. Their diverse music-making has proceeded largely without reference to the legacy of Schoenberg.
Aren’t we likewise entitled to ignore, perhaps even to hate, this new avian taxonomy—this abomination without names?
Not so fast.
Musical preferences are, in the first and final analysis, all about personal taste. I have a friend who professes to love the music of Karlheinz Stockhausen. (Google him.) I think that’s weird of my friend, but I wouldn’t say she’s wrong (or right) for enjoying Stockhausen’s Gruppen.
It’s different, though, with science. If someone were to profess that the world is flat, I would say that that person is wrong. Same thing with a profession that the Earth is at the center of our solar system. That’s not mere personal preference. Rather, that’s a matter of reality. I suppose there are those who would like for the world to be flat. And we all know that there were many persons who wanted the Earth to be at the center of our solar system. They felt so strongly about it that they executed someone—his name was Giordano Bruno—who disagreed with them. But that action, as drastic as it was, had no bearing—none whatsoever—on whether or not the Earth is at the center of our solar system.
So it is with “belief” in evolution.
No, I’m not about to bark up that tree. I’m not going to touch the evolution vs. Creation debate.
Rather, I’m going to address the following remarks solely and squarely at those who profess to, ahem, “believe” in evolution.
Just about the most brilliant insight of Charles Darwin is inarguably his least appreciated insight. Darwin clearly understood that evolution operates not at the level of groups or populations but rather at the level of individual organisms. Yes, evolution influences the traits that distinguish one population from another. But, again, evolution operates at the level of the individual.
It took fully a century for that great insight to be firmly and finally accepted by the scientific establishment. And the idea wouldn’t be transmitted to the general public until the publication in 1976 of Richard Dawkins’ dazzling and incendiary manifesto, The Selfish Gene.
Why? Why was there such resistance to the insight that evolution operates not on groups, but rather on individuals, or even their individual genes?
Darwin hints at an answer in this tease from that ominous Chapter 2 of Origin:
“Hence I look at individual differences, though of small interest to the systematist, as of high importance for us, as being the first step towards such slight varieties as are barely thought worth recording in works on natural history.”
Darwin isn’t just going up against those folks whom today we know as Creationists. Darwin is also going up against a powerfully entrenched scientific tradition of biological systematics.
Ever since Adam, we’ve been true believers—believers, that is to say, in the concept of the species. I’m not talking about this particular species concept or that particular concept, but rather in the more general notion that the species itself is somehow real. The idea of the species resonated perfectly with Plato’s vision of order and beauty in the universe. And the idea was eventually beatified in the scientific canon by that arch-Platonist, Carl von Linné—Latinized (of course!) to the more familiar Linnaeus.
Don’t get me wrong. I totally accept that the species concept is a useful way of organizing information about the world around us. But that doesn’t mean it’s right. That doesn’t mean it’s true. In this regard, I note that it’s useful, to be sure, to think in terms of sunrise, sunset, and the arc of the day—terms which constantly reinforce the impression that the Sun revolves around the Earth. Unquestionably, we think, as Isaac Newton did, in terms of “absolute” space and time. Yet we also know, thanks to Albert Einstein, that the distance between two objects depends on an observer’s position and velocity.
Aristotle’s geocentric solar system and Newton’s absolute space and time are, in some sense, alive and well. We live our daily lives according to Aristotelian and Newtonian precepts. We set our clocks according to events that play out on the Earth, not on the Sun. We operate motor vehicles, build bridges, and send rockets into space according to the principles of “classical,” or pre-Einsteinian, mechanics.
But we’re living a lie, so to speak.
We know that Aristotle and Newton—as brilliant as they were, and as useful as they still are—erected systems that are not, in an objective sense, true.
Shouldn’t we hold the Adam–Plato–Linnaeus concept of the species to the same standard?
The other day, my kids and I went sledding near our home in Boulder County, Colorado. We were having a grand old time, but the Sun was slipping under the western horizon (as per Aristotle!), and it was time to head home. As we trudged back through the new-fallen snow, we passed a big flock of birds roosting along the shore of Waneka Lake.
Naturally, we wondered what they were.
Not all that long ago, we would have shrugged them off as Canada Geese.
Then came the American Ornithologists’ Union, which in 2004 “split” the Canada Goose into two species—one called the Cackling Goose, the other retaining the old name of Canada Goose. Immediately, there was speculation, still ongoing—still downright rampant, I would say—that the “white-cheeked goose” complex might consist of yet additional species.
Let’s not worry about that right now. Let’s return to Waneka Lake.
What were those birds?
Well, there were big ones and small ones. There were medium ones. Some had long necks, others had short necks. Some had dusky-gray breasts, others had nearly white breasts, and a few had sandy-brown breasts. A few had bright white bands across the breast, but most did not. Some had short, stubby bills; others had long, sloping bills. Many of them said hink, but some of them said honk.
It was like something out of Dr. Seuss.
Well? What were they? The really big ones were perhaps moffitti Canada Geese. The really small ones were probably nominate hutchinsii Cackling Geese. The medium ones may have been mainly parvipes Canada Geese, but who knows?—big Cackling Geese and small Canada Geese overlap in morphology, plumage, and everything else. Which brings us to the bugaboo of the taverneri group of intermediate “white-cheeked geese,” doubtless present in small numbers—and maybe present in substantial numbers—in Colorado in the winter. Nobody knows. Nobody knows what taverneri is—or what they are. One subspecies? Two? Three? Are they Canada Geese? Or are they Cackling Geese?
(An aside to my birding pals who are way into the evolution and identification of “white-cheeked geese”: Why, I haven’t even touched the problem of paraphyly vis-à-vis the Barnacle Goose of Europe and the Nēnē of Hawaii!)
Dr. Seuss would have loved this.
Our decision out there at Waneka Lake was to enjoy the geese one bird at a time. Over there, the big one with a sandy-brown breast emblazoned with a white band. Right here, the medium one with a stubby bill but a relatively long neck. Out there in the water, the small one with the unmarked dusky-gray breast. Another medium one, this one with a shorter neck but an undeniably long bill. That group over there, of variably sized birds but mainly with white bands across their breasts. Those two big ones standing together, the ones with the pale breasts. Oh. They’re calling now. One of them is higher-pitched than the other. And here comes another medium one, this one with a stubby bill but a long, thin neck. (Right: Geese by © Bill Schmoker.)
The experience of studying those geese, one bird at a time, was exhilarating. And it was, as I hinted earlier, liberating. It is exhilarating and liberating to engage life on earth as it really is.
I accept that folks of my generation will continue to debate species concepts and species limits for as long as we’re alive. But I wonder about my kids. What about them? Will their generation finally throw off the shackles of Platonic thinking about the concept of the species? It is exhilarating and liberating to think that maybe, just maybe, they will do so.