Emergent simplicity in the supra-resonant dynamics and self-excited oscillations of insect flight

Since Anderson’s “More is different” and Schrödinger’s “What is life?”, physics has appreciated that the rules governing living systems may be irreducible to elemental components and hence emergent. Their composition matters. Locomotion arises from interacting physiological systems (neural, mechanical, muscular) all mediated through feedback from the environment. What sets living systems apart from simple active matter is that evolution has tinkered with this composition to produce behaviors that afford function. One of the most successful evolutionary examples of movement is the vast diversity of insect flight. Mechanical power costs to fly at small body sizes are high, dynamic stability is difficult to ensure, and yet thousands of insect species fly with quite different wingbeat frequencies, mass, and wing morphology. How do simple, common dynamical features emerge in this diversity? In this talk, I will use the agile flight of insects to show how an organismal physics approach can give insights into this emergent, functional simplicity. I will show how nearly all insects operate as resonant “spring-wing” systems to power flight but do not necessarily operate at their resonant frequency because of consequences for control. We will explore how insects have evolved two different strategies for powering this resonant flight system using muscles that either provide periodic oscillatory forcing or use stretch-responsive activation to set up self-excited limit cycles. While these two strategies seem dichotomous both in their evolution and their physics, we find that they can be unified in a single dynamic systems framework that shows how major evolutionary transitions reflect transitions in emergent dynamics. We embody this framework in robotic models demonstrating the transitions. We find that these two dynamic regimes are separated by a entrainment boundary but also bridged by a region of parameter space enabling smooth transitions between the two flight modes. These emergently simple dynamics can explain the repeated transitions and essential performance features underlying the evolutionary diversification between the two major flight modes of insects.