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When Koehl announced her plans to become a scientist, "her family wasn't the least bit of help," Vogel says. "Going to graduate school was ducking out of her responsibility to get married and produce another generation." Once, when her parents visited Duke, the family went out for a meal with Koehl's academic adviser, Stephen Wainwright '53. Wainwright, now a James B. Duke Professor Emeritus of biology, still recalls the drive to Chapel Hill: "Mama's sitting in the back seat. She says, 'Dr. Wainwright, don't you think it is totally wrong for young women to be studying to be scientists?' It was so unexpected, because there wasn't any lead-up to it, that I had to pull over and stop."
Wainwright, who has a reputation for launching Duke students into successful careers, provided the antidote to Koehl's upbringing. As with other students, he required her to take a British-style tutorial and write five research papers, which he critiqued rigorously. Pushed to excel, Koehl started to discover her own intellectual heft.
"Wainwright kicked her when she needed it and told her she was as good as anyone in the world," says Vogel.
Wainwright also introduced Koehl to comparative biomechanics, a then-emerging field that uses engineering principles to understand living organisms. The thought of studying the literal structure of life appealed to her. For her dissertation, Koehl explored how giant green sea anemones, whose squishy bodies she compares to water balloons, manage to withstand the violent waves of the Pacific coast.
Working on rocky Tatoosh Island, Washington, she rigged her electronic equipment to measure the water flow at the bottom of the channel where the anemones lived. She was puzzled when the meter registered hardly any flow at all.
"When it's raining and the waves are crashing and there's a lot of salt in the air, your electronics often suffer," she says. She rechecked her equipment before realizing the readings were correct: The animals had flattened themselves into inch-high disks and hidden in the slower-moving "boundary layer" below the turbulent waves. As a result of this behavior, she says, "these sea anemones are living in a microhabitat that's much more protected than what you would think if you just stood on the shore and watched the waves crash."
What's more, she learned, the anemones huddle together. "If you think about yourself standing in the surf with a bunch of friends around you, you realize that maybe you're protected from some of that really rapid flow," she explains. The discovery provided a lesson that still informs Koehl's research: If you want to understand how a creature survives, you have to view the world as that creature does.
Following up, Koehl analyzed two anemone species whose different body shapes allow them to thrive in different habitats. The resulting paper showed how an animal's design can affect both the forces it encounters and the way it reacts to those forces.
Koehl was working at the border of two established disciplines: solid mechanics (the design of organisms), which was Wainwright's specialty, and fluid mechanics (how those organisms interact with the surrounding air and water), which was Vogel's.
"Putting the two together, she got a system to tell her things that no one had ever even asked before," Vogel says. Her research "really gave you the picture of how the anemone was making it in the world that you didn't get from either field separately."
Koehl did a postdoctoral fellowship at the University of Washington's Friday Harbor Laboratories, then taught at Brown University. In 1979, she joined the Berkeley faculty and turned her attention to new questions, including one that had long vexed evolutionary biologists, and still does: How did insects develop wings that enable them to fly? The evolution from winglessness to working wings presumably entails intermediate generations with stubby wings that are too short for flight. Why would nature select for useless stubs over no wings at all?
But what if the short wings served another purpose? Could they have worked as parachutes or steering rudders even if they were inadequate for flight? Could they have served as tiny solar panels? What if they made an insect sexier? These competing hypotheses had been the subject of a lively debate among scientists.
To explore this question, Koehl teamed up with Joel Kingsolver '75, another Wainwright protégé who was now a postdoctoral fellow in her lab. Kingsolver, who had studied wings as solar collectors, knew about the debate. "There were a lot of ideas that had been proposed, but people hadn't really done anything quantitative with it," he says.
The Duke alumni decided to go the Mr. Potato Head route, building epoxy models of insect fossils, each with detachable wings. (Kingsolver, now a biology professor at the University of North Carolina at Chapel Hill, says he loved brainstorming with Koehl about these models. Once, he recalls, they were talking about how to build an aquatic insect. "Mimi said, 'Oh! You need something that soaks up water, holds it well, and wicks out to the edges. How about tampons?' ")
Adding and removing wings of different sizes, Koehl and Kingsolver tested their insects in a wind tunnel and under a heat lamp—a series of experiments that evolutionary theorist Stephen Jay Gould later called "elaborate and elegant." As they reviewed the data, the duo came to detect an evolutionary two-step. As long as insect bodies were small, their proportionately small wings were useless for flight, but they had another function: The longer the wing—up to a point—the better it absorbed the sun's heat and therefore helped regulate the insect's body temperature.
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