Saturday, May 23, 2009

On growth and form

As you may have noticed, I've had the 14 May issue of Nature in my bag all week and have yet to run out of things to think about.

This particular issue has a special Insight section on planktonic life in the sea. We don't pay much attention to these microscopic creatures, but in their teeming numbers they may be fabulously important in maintaining the planet's equilibrium.

Be that as it may, it was the "cover" of the special section that attracted my attention: a microphotograph of the silicate cell walls of various diatom species. Such beauty! Such symmetry! And in creatures so small. Suddenly I found myself thinking of D'Arcy Wentworth Thompson.

Thompson's On Growth and Form took its place among the classics of biology when it was first published in 1917. Cambridge University Press came out with a paperback edition in 1966, edited and with a preface by the eminent biologist John Tyler Bonner, which gave the book a bounce of popularity among my generation of young scientists. Those of us with even a modest literary bent recognized a work of striking originality and philosophical merit.

Thompson was the last of the old generation of classically educated biologists. He rejected natural selection as an sufficient explanation of evolution, looking instead to mathematical and mechanical constraints on the devlopment of organisms. Galileo said that the Book of Nature is written in the language of mathematics. Thompson was convinced that this included living things. His book pays particular attention to the beauty and symmetry of diatoms.

Thompson was both behind the times and ahead of the times. The mathematics he was able to bring to bear on life yielded only superficial insights into growth and form. Today's powerful computers apply mathematical algorithms even to the amazingly complex structures of proteins. And yes, as Thompson supposed, the Book of Life is indeed written in the language of mathematics.

Thompson retained a healthy sense of awe in the face of the life's complexity. In the Introduction to On Growth and Form he wrote:
How far even then mathematics will suffice to describe, and physics to explain, the fabric of the body, no man can foresee. It may be that all the laws of energy, and all the properties of matter, and all the chemistry of all the colloids are as powerless to explain the body as they are impotent to comprehend the soul. For my part, I think it is not so. Of how it is that the soul informs the body, physical science teaches me nothing; and that living matter influences and is influenced by mind is a mystery without a clue. Consciousness is not explained to my comprehension by all the nerve-paths and neurons of the physiologist; nor do I ask of physics how goodness shines in one man's face, and evil betrays itself in another. But of the construction and growth and working of the body, as of all else that is of the earth earthy, physical science is, in my humble opinion, our only teacher and guide.
It would be interesting to know to what extent Thompson would revise these opinions a century later. The mystery of consciousness still lies beyond our grasp, although most biologists would not say beyond the realm of the "earth earthy." We still don't have a clue why goodness shines in one man's face and evil in another. For this, the great works of classical literature so beloved by Thompson have as much to teach us as do his equally beloved mathematics and physics.