The Mechanics of Natural Success: Bioengineers View Physics as a Lever on Evolution

By Wickelgren, Ingid | Science News, June 17, 1989 | Go to article overview

The Mechanics of Natural Success: Bioengineers View Physics as a Lever on Evolution


Wickelgren, Ingid, Science News


The Mechanics of Natural Success

Eliminating the impossible may seem like a long way to the truth, but in the search for truth in nature, it could provide a shortcut. Looking at the natural world in the form of individual molecules, especially genes, makes biological variation seem boundless. But watch diverse forms of foliage fold or wildlife walk, wiggle or hang from trees, sharing the same techniques to tackle the physical world. And notice: While round and cylindrical organisms abound, there are almost no square ones, no organism's skeleton is made of metal and very few use any kind of wheel for transport. Why not? It's elementary, my dear Watson: physics.

Evolution does not seem to favor right angles, metallic skeletons or wheels because these features are not good mechanical solutions to the problems most organisms face. Flat surfaces that joint at right angles function poorly, compared with curves, when they must resist internal or external pressures. Metals make good permanent structures, but not ones that must grow and adapt to environmental changes. And the planet's relative scarcity of metals makes it energetically impractical for an organism to assemble large quantities of them. Wheels are difficult to maneuver around obstacles or to keep stable over bumps, and they are nearly useless underground or in the air.

"Every organism has mechanical things to worry about, however good its reproductive capabilities might be," says biologist Steven Vogel at Duke University in Durham, N.C. Trees must withstand high winds; mammalian skeletons must remain stable but flexible; filter-feeding marine organisms must capture food froma dilute ocean; pinecones must trap pollen from the airf prairie dogs must construct burrows with plenty of ventilation. Evolution cannot tamper with gravity; nor can it alter the Earth's mineral distribution, the way the wind blows or the surface-to-volume ratio of a given size and shape. Natural selection must work with or around certain mechanical and geometric givens.

With such factors in mind, an increasing number of biologists have been mixing mechanics into recipes that explain the natural world. Their approach, called comparative biomechanics, contrasts with most of contemporary biology, which tends to focus on molecules and cells. Mechanically oriented biologists study how an orgnism's form and function evolved in the context of its physical environment. And their investigations reveal that many reasons for the evolved traits of living creatures lie not in genetics, cellular interactions or ecological relationships, but rather in immediate-world physical principles.

Nature's physical forces affect all organisms -- animal and plant, living and extinct. They can work on an organism's insides or its outside, through fluids or directly on solids. Scientists in the field of comparative biomechanics have studied nearly every phylum on the planet and the ways in which mechanical forces have shaped their evolutionary histories. "With the aid of a little engineering, we can start recognizing the general principles underlying the mechanics of being a successful organism," Vogel says.

Comparative biomechanics dates back to the days "when biology and physics weren't really separate," Vogel says. For example, "Galileo and da Vinci worried equally about the living and the nonliving." But over the next few hundred years, biology and physics grew apart, and did not reunite until the 1930s, when Sir James Gray at England's Cambridge University began his work on mechanical principles of animal locomotion. The most recent resurgence of interest in comparative biomechanics began in the mid-1970s at Duke and Cambridge, and now about two dozen teams worldwide work in the field, Vogel says.

Applying physics to the study of biology can explain similarities among seemingly diverse creatures. By comparing the structural geometries and skeletal stresses of mammals ranging in size from squirrels to horses, one bioengineer has come up with what he proposes as the main design principle for the mammalian locomotor skeleton. …

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