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How the Raven Said “Nevermore”


Does Darwinian evolution explain how things came to be? This has been its greatest success, according to many scientists, historians, and journalists. Darwin provided a mechanism that drew together a huge number of disconnected observations and organized them into a theory of progress — the tree of life — that explained the origin of novelties both small and great. And yet when we look in detail at the explanations for specific traits, we often find the notorious Darwinian “just-so stories” that convey no serious explanation at all. 

If something exists and looks advantageous, there must have been some mysterious “selection pressure” that forced it toward its current level of “fitness,” whatever that is (presumably, the fact that it exists). But since natural selection is synonymous with motion toward fitness, this reduces to, “Evolutionary pressure caused evolution,” or simply, “It evolved because it evolved.” Let’s see how this style of reasoning works by examining a paper that purports to explain the origin of the syrinx in birds.

“It Evolved Because It Evolved”

Mammals have a larynx; birds have a syrinx. The primary difference is in the location of the sound generator with respect to the windpipe (trachea). In mammals, the vocal folds are at the top, and the resonator (windpipe) is below. In birds, the vocal folds are at the bottom, and the resonator is above. Both mechanisms work extremely well. Humans can produce three-and-a-half octaves from bass to soprano, with all the history of song bearing witness to its effectiveness. Birds also exhibit tremendous range and variability with the syrinx organ, from croaks of ravens to sweet songs of the nightingale and the elaborate, rapid cadenzas of meadowlarks. How did the sound generator move from one end of the resonator to the other, and why? 

When reading evolutionary explanations, one must stay focused on the question. Many scientific papers load up on jargon and details about traits. This is good and helpful, but can be distracting. We want to know if evolution explains the origin of the trait. The paper in PLOS Biology by Riede et al., “The evolution of the syrinx: An acoustic theory,” is a perfect example of sound and fury about traits, signifying nothing about origin. It is loaded with anatomical and acoustical details. The authors experimented with chickens, parakeets, and zebra finches, measuring the efficiency of sound production as a function of anatomy. But when it comes to explaining how the syrinx originated by blind processes of evolution, the specter of speculation rises up like a ghost, speaking tales of mysterious possibilities. Here is the operative paragraph:

The current study highlights vocal efficiency as an important selective force that may have played a role in the evolution of the syrinx as a vocal organ. The timing of the transition from larynx to syrinx in the theropod lineage leading to modern birds is unknown prior to 66–68 million years ago. Whereas clarification awaits new fossil data, the results from this study allow some speculation about a possible scenario and therefore the timing of syrinx evolution. [Emphasis added.]

What is a “selective force?” Is it a law of nature, like electromagnetism, that can be specified mathematically at high precision? Can it make predictions? Does it display reproducible regularities? Can an evolutionist say, “Given that vocal efficiency is adaptive, it acts as a force that will cause a theropod dinosaur to evolve a syrinx in 30 million years”? If that were the case, vocal efficiency should converge on the syrinx design in every animal group. 

Providing an Out

But they provide themselves an out: vocal efficiency is “an” important selective force, not “the” only one. It only “may have played a role” in the explanation. So if “selective force + x” led to the result, which one was necessary or sufficient? It’s like the old middle-school trick, “My dad and I can answer any question.” The listener asks a hard question, and gets the response, “That’s one of the questions my dad knows the answer to.” Dad, conveniently, is far away somewhere. When a scientist trades in stories that “allow some speculation about a possible scenario,” he deserves to be taken as seriously as the student whose dad knows everything. These authors insert a possible x, but then add a y. The new scenario equation becomes, “natural selection + sexual selection + y” —

This initial investigation of possible selective advantages of a syringeal location of the sound source also highlights that the evolutionary origin of novelty can be addressed with specific tests of hypotheses about selective scenarios. Our data show that one likely selective advantage of the syringeal position is increased efficiency. The ability to generate loud sounds is important for long-range acoustic communication and in the context of courtship and territory defense. Thus, both natural and sexual selective forces may have contributed to the evolution of the avian syrinx. To what degree an early syrinx may have coexisted with a laryngeal sound source remains to be determined.

Darwinism serves as an evolving scenario. Given that the syrinx exists, and works efficiently, the authors’ anatomical results “allow some speculation about a possible scenario” about how it came to be. And because they (and the journal editors) are pre-committed to only Darwinian scenarios from the outset as the only permissible class of explanation, they become oblivious to the circular reasoning in their story. It evolved because a “selective force” (or a combination of selective forces) pushed it to evolve. In short, it evolved because it evolved. And yet explaining the origin of the syrinx was the purpose of the paper:

Our approach has addressed the origin of the syrinx as opposed to its diversification. It is therefore imperative to assume a simple sound source, rather than the diverse morphologies found in extant birds. Once the relocation of the sound source had occurred in an as of yet unknown ancestor of Aves, the further diversification may have explored many different avenues for further increasing vocal output, such as two sound sources, different interactions with the upper vocal tract, etc. The different mechanisms of interaction suggest a possible, albeit speculative, scenario for the origin of the syringeal sound source within Aves.

To preclude such fact-free speculation, science needs alternatives. Only when intelligent design has been ruled out of court can blatant speculation get published in a science journal. Many times, evolutionists hide their miracles in vague language, such as “Once the relocation of the sound source had occurred” — but the relocation is the very thing needing explanation. How did it occur? Numerous sub-questions are concealed beneath that blanket that should be aired:

  • Did it “occur” or was it always the way we see it now?
  • Why didn’t the laryngeal sound source improve where it was, instead of relocating?
  • Where was its original position? Who was the ancestor, and where is the evidence?
  • Was each stage in the relocation adaptive? 
  • Where are the transitional forms?
  • Was each new form so advantageous that all the birds without it died out? (The “cost of selection”)
  • Did each step include brain software so the bird would know how to use it?
  • How many coordinated mutations would be required?

Readers can think of many more such questions to ask. Darwinian gradualism demands that each step not only aid fitness, but spread throughout the population. In this case, an unknown theropod ancestor, passing through an unknown number of stages, yielded a bird with a fully formed syrinx organ in the optimum place for exquisite vocal efficiency.

From Origin to Diversification

Given the basic structure of a syrinx, a sound source at the bottom of the windpipe, birds showcase astonishing variations on the theme. Some birds, such as herons, have long necks with a long trachea; others, such as ducks, have short necks with a short trachea. The length and diameter of the windpipe is tuned for each species’ ability to push air through it and get the optimum sound output. An ostrich with a thin long neck can vocalize as efficiently as a tiny hummingbird. Design theorists might disagree on the extent to which natural selection is responsible for diversification, once the syrinx exists. To evolutionists, though, “selective force” is the only tool in the toolkit. Notice how the authors once again shield natural selection’s magic in cloudy verbiage, saying, “the further diversification may have explored many different avenues for further increasing vocal output….” The subject-verb structure is curious. Does diversification explore? Is diversification an active agent, trying to find something? 

Promissory Notes

The authors admit that vocal efficiency is complex, involving a number of anatomical features. If they cannot account for the relocation of the sound source without speculating wildly, good luck accounting for the other features. Other evolutionists will have to tackle that somewhere over the rainbow.

The modeling and the experiments conducted here deliberately constitute a test of a limited and small set of parameters rather than a physical replica of the avian vocal organ, with all its complexity. While this minimalist approach is likely to inform about a possible selective advantage for the switch in source location, it does not include a thorough test of other selective scenarios and does not explore other likely adaptations for increased efficiency in extant birds. Therefore, future work will have to test whether the dramatic efficiency advantage of a syringeal position is maintained for various syrinx designs or if other variables emerge as the main targets of selection. Syrinx morphology shows remarkable diversity, including features such as multiple sound sources, multilayered vocal fold design, or changes in vocal tract design and motility. All of these features affect efficiency, and we do not know how they are influenced by trade-offs between vocal efficiency and those other acoustic features. Nevertheless, our approach presents a first test and sets the stage for testing additional hypotheses related to syrinx origin and syrinx diversification.

The authors just used the word “design” three times: 

  • “various syrinx designs
  • “multilayered vocal fold design
  • “vocal tract design and motility”

As Darwinians, they would call these instances of “apparent” design, not real design. According to the thesis of Michael Behe’s new book Darwin Devolves, though, each step would require breaking an existing functional element. It’s hard to imagine the syrinx as the end result of a long chain of broken things.

Photo: A raven, by Peter Lloyd via Unsplash.