Illuminated Life

Meet the true masters of optics: Animals that know a lot more about slicing, dicing, and twisting beams of light than we do

By George M. Whitesides, Felice Frankel|Saturday, August 06, 2005

The manipulation of light seems, at first blush, a uniquely human achievement. It shows up in the green-yellow-red of traffic lights, the garish neon of an urban streetscape, and the shimmering colors of an evening gown. It also lies at the heart of two quintessential modern technologies: lasers that radiate beams of staggering purity and intensity and optical fibers that direct those beams to telephones, televisions, and computers around the world. We think, proudly, that we are the first species to make light do our bidding.

A little humility is in order. Many other organisms have developed their own, equally cunning ways to control the color and movement of light, as the photographs on these pages illustrate. Peacocks sport tail feathers with finely grooved structures that split apart sunshine, wave by wave, and sort it into shimmering bands of color. The iridescent azure gleam of the morpho butterfly results from a related form of optical engineering. Scales on the insect’s wings are spaced such that waves of red light cancel themselves out; by elimination, the waves that reach the eye appear electric blue. Even Venus’s flower-basket—a sponge, one of the most primitive of creatures—has a sophisticated flair for controlling light. Its skeleton is a network of optical conduits that diffuse light from its core to its periphery.

These solutions reflect the relentless logic of natural selection at work. A peacock relies on elaborate plumage to stand out in order to attract a mate. If he cannot command the attention of a peahen, he will not bequeath any little peafowl to the next generation. The fiercely territorial morpho butterfly probably flashes its colors to guard its food and mates by warning others of its kind to stay away. Biologists are still puzzling over the function of the flower-basket’s unique network of living optical fibers. One theory is that the sponge’s transparent framework collects the glow from luminescent, symbiotic microbes and concentrates it into a network of miniature spotlights that attract prey.

Sometimes nature’s optical tricks arise incidentally, as by-products of other innovations. Marine mollusks benefit tremendously from protective shells—structures that must be strong and tough but buildable using only the nutrients available in seawater. The creatures fabricate their shells by alternating layers of calcium carbonate with layers of gluelike protein. By happenstance, the alternating layers act as tiny prisms, adding rainbow tinges to the light they reflect. The result is the delicately colored milky sheen of mother-of-pearl.

It is difficult not to stand in awe before these biological light manipulations. The grooved structure of the peacock feathers splits light in the same way as a diffraction grating, a tool invented by 19th-century physicist Joseph von Fraunhofer to discern the nature of sunlight. The flower-basket’s skeleton directs light where it is needed, just like modern optical fibers. Butterflies create color by selectively adding and deleting certain wavelengths of light. Physicists have only recently devised comparable materials, called photonic band-gap crystals, and are now exploring their use in phone switches, solar cells, and antennas.

No surprise, then, that some engineers are looking to the living world for the next generation of optic inspirations. Applying the solutions of biological evolution to our purposes is a time-honored technique. Velcro is based on the stickers on a burr, and compound optical lenses were certainly stimulated by the eyes of insects. So far, there are no products that effectively mimic the wings of the morpho butterfly, but only because we do not yet know how to fabricate optical structures of that complexity.

Of course, nature has had hundreds of millions of years to test and refine beneficial types of optical engineering; we have been at it for just a few hundred years. More than humility, perhaps, what we truly need to conjure is respect in the presence of creatures such as the magnificent morpho. This uncomplicated creature still has much to teach us about using light.

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