Biological structures usually appear more complicated up close, and the fly wing is no exception. Maneuverability hinges on a hinge: a “unique and incredibly complex biomechanical hinge” that is flexible but strong. A new study reveals its intricacies in unprecedented detail.

Dr. Michael Dickinson at Caltech has been fascinated by insect flight for much of his career. A professor of bioengineering and aeronautics, Dickinson has even built tiny flight simulators and wind tunnels for fruit flies to observe their capabilities. His latest work on insect flight, announced by Caltech, was published in Nature by Melis, Siwanowicz, and Dickinson. Nature posted a video the same day about the findings. It is accompanied by the headline, “AI and robotics demystify the workings of a fly’s wing.” Readers are encouraged to watch the 5-minute video on YouTube as an introduction to this article.

“Wholly Original Appendages” 

Noteworthy in the opening is the statement that insect wings are “wholly original appendages” unlike the wings of the other three classes of powered flyers — birds, bats, and pterosaurs — assumed to be modified limbs. This makes it hard to claim that insect wings “evolved” from pre-existing structures. The video shows a rotating animation of at least 15 parts in the “unique and incredibly complex biochemical hinge” shown in operation. The hard parts, called sclerites, fit together with flexible joints like pieces of a challenging 3-D puzzle.

Dickinson’s team was able for the first time to study the hinge’s motion on live flies. The researchers combined imaging and machine learning to understand the functional interactions of all the parts in the hinge — “a huge challenge” for such tiny creatures that dart about rapidly and take off in a blink. “Insects are some of the most agile flyers on the planet,” the narrator says. Data collection included filming 70,000 individual wingbeats with high-speed cameras recording at 15,000 frames per second. Then, after molding facsimiles of each individual part for study, and creating computer models of the interactions, the Caltech team built a computer model of the hinge and tried to imitate it with robotics. 

Only 12 neurons control flight in insects, attached to 12 muscles that respond to commands from these neurons. Some commands initiate the wingbeat and other commands tweak the commands for the fly’s repertoire of aerobatics. Certainly the resulting functional whole is more than the sum of the parts, because the interdependent muscles, like a dance troupe, work cooperatively and are tied into the fly’s sensory systems.

To learn which muscles operate which parts of the hinge, the team genetically engineered flies with fluorescent proteins they could watch light up in the slow-motion videos. Data about the inputs (the muscles) and the outputs (the wing motions) were used to train a neural network. The result, the narrator says, was “a simulated model they could manipulate in ways that would be impossible in real life.” Even so, they did not fully understand how the commands translate into “the kind of aerobatic feats insects are so good at.”

That’s where robotics entered. They built a “flapping model” they could program with the commands they had deciphered. It allowed them to map the muscle activities with the resulting flight forces. The match between the robot and real flies was pretty good. “It’s not the complete picture,” the narrator confesses, but 

the range of hypotheses this work led to could, eventually, provide an insight into the innovations that underlie the evolution of all flying insects. [Emphasis added.]

Alert! Fly in the Ointment!

The ointment of scientific explanation just suffered spoilage with that ending line. I am often baffled at statements like that in journal papers. They will wax eloquent over the sophistication of some biological wonder, only to spoil the awe with a claim that it evolved by blind, material processes. Even after admitting that the robotic model made with Caltech’s intelligent design amounted to a poor substitute for the living fly, the narrator ended on a Darwinian note. 

As usual, any “insight into the innovations that underlie the evolution” of biological wonders was stated in future tense with a promissory note. In the accompanying News and Views piece about the research in the same issue of Nature, Tanvi Deora fell into line:

Winged insects, including butterflies, wasps and beetles, are some of the most successful animals on the planet, in terms of numbers of species and of individuals. Part of this success comes from their ability to fly and from the evolution of wings, which have evolved as a new type of appendage, independently of limbs. The wing is connected to the insect body through an exquisite hinge.

Deora ended with a final polish on the narrative gloss, promising that the research “will enable us to understand the wing hinge as well as its evolutionary importance to the mechanisms for flight control.”

What Do Evolutionists in the Lab Really Think?

Dickinson strikes me as deserving of a Nobel Prize for the diligence of his scientific work. In previous papers I have sensed his awe at fruit flies to the point where he urged his readers, “think before you swat.” Does the swatter realize what was just squashed? Is it like Bambi vs. Godzilla, or Dr. Fake bombing the Eiffel Tower? It’s not that Dickinson would prevent the swatter from committing the dastardly deed, or would never swat a fly himself, but the statement implies a feeling of melancholy at seeing something so wonderful destroyed. Being a member of academia, though, he had no other option but to say, “it evolved.”

“The fly wing hinge is perhaps the most mysterious and underappreciated structure in the history of life,” says Michael Dickinson, Caltech’s Esther M. and Abe M. Zarem Professor of Bioengineering and Aeronautics, and executive officer for biology and biological engineering. “If insects had not evolved this very improbable jointto flap their wings, the world would be a very different place, absent of flowering plants and familiar creatures like birds, bats — and probably humans.”

 Fortunately, Dr. Dickinson is motivated by some other nobler goals:

The ultimate goal is to understand the neurobiological connection between a fly’s brain and the movement of its wings. “The wing hinge is just the hardware; the real passion in our lab has been the brain–body interface,” Dickinson says. “We want to understand the circuitry between the biomechanics and the neurobiology. Very few times in evolution has an animal had one very successful form of locomotion — walking — and simply added another one — flying. This means that the brains of insects must have all the circuitry to regulate to completely different means of moving.”

Without the crutch of evolution, these motivations could be taken up by design advocates with knowledge of engineering and, I believe, with more gusto and appreciation. There will be no shortage of work to do. This project involved a simple fly, but what about the hundreds of thousands of variations in the wings of other insects? From large beetles to tiny gnats, from dragonflies to monarch butterflies, the implementations of wing design in insects may never be fully explored.

And yes, you can swat without guilt the fly that invaded your house. There are plenty more of them where it came from. But if the world had a billion Mona Lisas or 5 billion smartphones (it does have that), would familiarity breed contempt? Would we fail to acknowledge the art or engineering in well-designed items, even if they were commonplace? 

Next time a fly lands on the outside of the window, maybe it would be worthwhile to look at it for a moment and think of all the years of work it took Caltech scientists to try to understand one little part — the “unique and incredibly complex biomechanical hinge” that connects the wings to the muscles. Take another moment to watch the little guy dart about with maneuvers that would astonish a daredevil in an air show. Gaze at the complex eyes, antennae, and limbs. Watch the fly land on glass and walk up without falling. Understanding any one of those things could occupy the lifetime careers of an army of bioengineers.