Linnaeus's Luck?

Natural History, Sept, 2000 by Stephen Jay Gould

Why does the great creationist's system of classification work in Darwin's world? And what does the resolution of this paradox teach us about the importance and fascination of taxonomy?

Carolus Linnaeus (1707-78), the founder of modern taxonomy, frequently cited an ancient motto to epitomize his view of life: Natura non facit saltum (Nature does not make leaps). Such unbroken continuity may rule in the material world, but our human passion for order and clear distinction leads us to designate certain moments or events as "official" beginnings for something discrete and new. Thus, the signatures on a document define the birth of a nation on July 4, 1776, and the easily remembered eleventh hour of the eleventh day of the eleventh month (November 11, 1918) marks the armistice in a horrible war supposedly fought to end all contemplation of future wars. In a small irony of history, our apostle of natural continuity also became the author and guardian of a symbolic leap to novelty, for the modern taxonomy of animals officially began with the publication of the definitive tenth edition of Linnaeus's Systema Naturae in 1758.

The current classification of animals may boast such a formally recognized inauguration, but an agreement about beginnings does not guarantee a consensus about importance. In fact, the worth assigned to taxonomy by great scientists has spanned the full range of conceivable evaluations. When Lord Rutherford, the great British physicist (born in New Zealand), discovered that the dates of radioactive decay could establish the true age of Earth (billions rather than millions of years), he scorned the opposition of paleontologists by branding their taxonomic labors in classifying fossils as the lowest form of purely descriptive activity, a style of research barely meriting the name "science." Taxonomy, he fumed, could claim no more intellectual depth than "stamp collecting"--an old canard that makes me bristle from two sides of my being: as a present paleontologist and a former philatelist!

Rutherford's anathema dates to the first decade of the twentieth century. Interestingly, when Luis Alvarez, a physicist of similar distinction, became equally enraged by some paleontologists during the last decade of the twentieth century, he invoked the same image in denigration: "They're not very good scientists; they're just stamp collectors." I continue to reject both the metaphor and the damning of all for the stodginess of a majority, for Alvarez had exploded in frustration at the strong biases that initially led most paleontologists to dismiss, without fair consideration, his apparently correct conclusion that the impact of a large extraterrestrial body triggered the mass extinction of dinosaurs and about 50 percent of marine animal species 65 million years ago.

The phony assumption underlying this debasement of taxonomy to philately holds that the order among organisms stands forth as a simple fact plainly accessible to any half-decent observer. The task of taxonomy may then be equated with the dullest form of cataloging--the allocation of an admittedly large array of objects to their clearly preassigned places: pasting stamps into the designated spaces of nature's album, putting hats on the right hooks of the world's objective hat rack, or shoving bundles into the proper pigeonholes in evolution's storehouse, to cite a standard set of dismissive metaphors.

In maximal contrast, the great Swiss zoologist Louis Agassiz exalted taxonomy as the highest possible calling of all when, in 1859, he opened Harvard's Museum of Comparative Zoology in his adopted land. Each species, Agassiz argued, represents the material incarnation on Earth of a single and discrete idea in the mind of God. The natural order among species--their taxonomy--therefore reflects the structure of divine thought. If we can accurately identify the system of interrelationships among species, Agassiz concluded, we will stand as close as rationality can bring us to the nature of God.

Notwithstanding their maximally disparate judgments of taxonomy, Rutherford and Agassiz rank as strange bedfellows in their shared premise that a single objective order exists "out there" in the "real world" and that a proper classification will allocate each organism to its designated spot in the one true system. (For Rutherford, this order represents a basically boring and easily ascertainable aspect of macroscopic nature--too far removed from the atomic world of fundamental laws and causes to generate much scientific interest or insight. For Agassiz, in greatest conceivable contrast, this order represents our best shot at grasping the otherwise ineffable nature of God himself.)

In framing a modern Goldilockian defense of the importance of taxonomy--far warmer than Rutherford's icy indifference but not quite as hot as Agassiz's impassioned embrace--we must begin by refuting their shared assumption that one true order exists "out there" and that correct classifications may be equated with accurate maps. We can best defend the scientific vitality of taxonomy by asserting the opposite premise: that all systems of classification must express theories about the causes of order and must therefore feature a complex mixture of concepts and percepts--that is, preferences in human thinking combined with observations of nature's often cryptic realities. Good taxonomies may be analogized with useful maps, but they reveal (as do all good maps) both our preferred mental schemes and the pieces of external reality that we have chosen to order and depict in our cartographic effort.