LIFE'S OTHER SECRET

Spectacular as the advances in genetics have been, the DNA molecule tells only part of the scientific story of life; much of the rest, this work argues, is built upon physical and mathematical principles only now being recognized. Stewart, who writes the ``Mathematical Recreations'' column for Scientific American, credits much of the groundwork for this study to D'Arcy Thompson, a Scottish biologist who died in 1948. The atoms of living beings are indistinguishable from those in a laboratory flask. Thompson's approach to this problem was to apply the laws of physics and mathematics to the shapes of living beings, from cells to complete organisms. Minimal surfaces, like those defined by soap bubbles, dictate that many small organisms will take the shape of regular solids. The spiral structures of other organisms, from shellfish to flowers, embody the Fibonacci series, a simple mathematical relationship. The markings of other creatures, from tropical fish to tigers and zebras, can be described by elegant mathematical formulas. As Stewart points out, these patterns are produced by genetics and evolution; but they can only be explained by examining the mathematical laws that genetics and evolution must conform to. With that in mind, Stewart takes the reader on a tour of the forms and structures of living things. We see the elegant symmetry of DNA and the geometry of viruses and cells. The evolutionary component of the subject is not neglected, e.g., the profound change of Earth's atmosphere to one with a large component of free oxygen required geometric strategies for organisms to protect themselves from the reactive gas. And new mathematical tools (fractals, chaos theory) as well as computer graphics programs are opening up the subject to study on a scale Thompson never could have achieved. Stewart makes his case in fascinating detail and with an easy, readable style that should make this material accessible to a wide range of readers. (100 drawings and photos, not seen)