Studying how animals do the locomotion

Radcliffe Fellows look at dragonflies, snails, and modern dancers

By Corydon Ireland

Harvard News Office

Z. Jane Wang, a Radcliffe Fellow this year, is a physicist interested in flapping flight, a form of locomotion used by two-thirds of all species, including insects, birds, and fish. (In physical terms, the movement of fins and wings is the same.)

Wang has written about the physics of dragonfly flight, a complex puzzle of aerodynamics that is 350 million years old. She’s also looked at why butterflies seem to lurch through the air, and has studied the way leaves fall so floatingly — which is similar, said Wang, to the physics of insect flight.

Physicist Anette “Peko” Hosoi, also a Radcliffe Fellow, is an expert in small-animal locomotion. She’s written about burrowing clams (they’re fast, digging at one centimeter per second) and has studied the sticky, steady snail — a creature she calls “nature’s ultimate all-terrain vehicle.”

The two young scientists, both graduate students a decade ago at the University of Chicago, are sharing an academic year of collaboration and conversation at the Radcliffe Institute for Advanced Study with 50 other fellows — about a quarter of them scientists.

“We’re both interested in locomotion in fluids,” said Wang, an associate professor of theoretical and applied mechanics at Cornell University.

In science, the classic fluids are air, water, and oil. So there is common ground in studying the fluid mechanics of how creatures fly through air or wiggle through water.

Locomotion illuminates two big questions for scientists, said Hosoi, an associate professor of mechanical engineering at the Massachusetts Institute of Technology (MIT).

For one, understanding how things move gives biologists insight into evolution. Studying fruit flies in flight, for instance, can reveal subtle changes in wing movement between species that evolved at different times.

Understanding the mechanics of how things move can also “inspire design,” said Hosoi, by helping engineers understand the efficiencies of motion. At MIT, she and graduate students study the way creatures swim, hop, crawl, fly, and slither — a kinesthetic portal onto efficiencies that have evolved over time.

The subject matter — hopping, crawling, flying — may seem whimsical, but the potential applications are not. In Hosoi’s lab is a sure-footed 10-inch robotic snail that one oil company may use to explore test holes dug thousands of feet into the ground and fouled with gluelike drilling mud. “You need something down there that’s not going to get stuck,” she said.

Along similar practical lines, Hosoi is helping a Cambridge-based robotics company find the best way to efficiently anchor autonomous underwater vehicles. Nature may have an answer: the lowly clam, whose sticky pendant foot is “two orders of magnitude better than any [man-made] anchor we have — hugely better,” Hosoi said.

But applications are not the real inspiration for studying the way things move, said Wang. “We like to know how things work.”

There are aesthetic considerations too, she said. “We’re most interested in dragonflies,” she said, “partly because they’re beautiful and agile.” (In her Cornell lab, dragonflies are tethered for ease of observation.)

In graduate school, Wang studied both statistical physics of turbulence and random matrix theory, a way of using mathematics to study the structure of physical systems.

Hosoi studied instabilities in thin films, which are natural or man-made material layers that can be as thin as a few atoms.

Both gravitated to the serious study of the way things move. While doing postgraduate work at Oxford University, Wang came across a little book on the mechanics of flying and swimming. The fluid dynamics of insect flight, it turned out, were still little understood — and that inspired Wang to study what she calls “this little oddity” of science.

Hosoi turned to locomotion at MIT, after every graduate student who applied to work with her wanted to build a robot.

That led Hosoi to combine her academic specialty, fluid dynamics, with the idea of machines that move interactively through an environment: “I started studying locomotion,” she said. “It turned out to be a gold mine. There are all kinds of good problems in the field.”

At Radcliffe, Hosoi — and Wang especially — have added a twist: regular conversations with Radcliffe Fellow, modern dancer, and Martha Graham protégé Christine Dakin. “This being Radcliffe, you just talk to people,” said Wang — in this case about the confluence of scientific and artistic perspectives on movement.

“At this point it’s a conversation,” said Hosoi about interactions with Dakin. “But that’s how great things start.”

“It struck me immediately, what they were doing,” said Dakin of her new scientific friends. “My perspective in the world is watching movement.”

She hopes to explore with them what makes locomotion so fascinating and pleasing to people — though no dance movement or other practical outcome will necessarily follow. “This is exploration,” said Dakin.

She invited Wang to her Zen-like Concord Avenue studio to demonstrate some Martha Graham dance techniques — intentional sequences of falling and rising that themselves are like the spiraling of a free-falling leaf, said Dakin, or the blurring figure-eights of a hovering dragonfly.

She also attended “A Day of Locomotion” at the Radcliffe Gymnasium, an Oct. 16 afternoon of scientific presentations organized in part by Hosoi and Wang. Talks included those on robotic snails, burrowing razor clams, simulated perching, insect flight, human walking, and filament-tailed microswimmers.

Hosoi investigates microswimmer locomotion, especially what she called a model system for studying the energy expenditures in a single natural task: the brainless, noneating, single-goal progression of motile sperm.

Engineers, she said, like to study how natural organisms move in ways that minimize caloric expenditures.

Wang uses the hovering insect as a system for studying optimization in the natural evolution of flapping flight, and is currently investigating patterns of flight in multiple species of fruit flies in connection to their genetic history.

The hovering insect is an extreme case of optimized locomotion, she said. “It’s expensive to stay in the air” during hovering, a complex interplay of air and wings that expends up to 200 times an insect’s basal metabolic rate.

“We don’t know if this implies that insects minimize energy expenditures,” she said, “but it raises the question: Do they?”

Among Radcliffe Fellows, questions fly around like shooting stars, and scientists add their own arts and inquiries to the show of lights.

“We’re getting the very best scientists to apply for fellowships — like Jane and Peko,” said Barbara J. Grosz, interim dean of the Radcliffe Institute and Higgins Professor of Natural Sciences at the Harvard School of Engineering and Applied Sciences. “Having the best people in a field is why Radcliffe works.”

The idea of Wang, Hosoi, and Dakin in conversation embodies the Radcliffe Fellows experience, she said: “a roomful of people from different disciplines, thrilled to collaborate with each other.”

corydon_ireland@harvard.edu