Passage IV

NATURAL SCIENCE: This passage is adapted from The Variety of Life by Colin Tudge (©2000 by Oxford University Press).

Through all classification systems, whether devised by songbirds, professors of botany, of fishmongers, two separate sets of considerations run in parallel. The first is operational: how do you actually go about classifying? what criteria do you adopt to decide whether item A belongs in category X or category Y? A songbird weighing up a bird of prey perhaps looks for curvature of break or length of claw—or, more probably, relies on overall impression or gestalt; and by such means it distinguishes a falcon from a duck. For chefs, succulence on the inside and a crunchy carapace on the outside are the marks of shellfish.

If the criteria are made explicit, and can be repeated by other people simply by following the instructions—if, for example, they depend on qualities that can be measured and are not judged simply according to personal taste—then those criteria can be called 'objective'. But objective criteria may also be arbitrary. I might, for example, decree that all insects with legs over 2 centimeters long should be placed in a new grouping called 'mega-insects'. The criterion would be perfectly objective, in the sense that it is explicit and repeatable, which would not be the case if I simply decreed that there should be a special category marked 'beautiful'. But although the grouping of mega-insects would be objectively defined it would also be arbitrary. Nothing very special distinguishes insects that just happen to be large, except their largeness.

Behind all classifications, too, there is inevitably a philosophy. All classifications impose some view of the world: they all make a statement. Thus a chef regards the Universe as a market: the things within it are divided up according to edibility and wholesomeness. A songbird is concerned with food, too, but also with enemies and potential mates. The many classifications devised by scientists, historically, have pursued various philosophies.

Whatever criteria we adopt, however, and whatever we are classifying and for whatever purpose, all classifications tend to follow a common pattern. The items in question are first divided into big categories, and then each big category is divided into smaller categories, and so on. The result is a series of nesting groups called a hierarchy: little ones grouped within bigger ones still. Classifications, in short, tend to be hierarchical.

Ad hoc ways of categorizing living things are useful. Long may they persist. Practical people doing practical things need to carve up the world in their own ways, and it is not for outsiders to cavil. The flesh of abalones (ear shells) and of lobsters are comparably tender even if those creatures are less closely related to each other than eagles are to sea squirts; so why not call them both 'shellfish'? A 'weed' is a useful category, as any farmer will attest. Each system of classification casts its own light upon the world; lay different classification side by side and you illuminate from different angles, and truly begin to see in three dimensions.

But it is one thing simply to manipulate aspects of nature for own convenience, and another to seek understanding. Of course, deeper understanding can lead to more subtle exploitation—and thus it is, for example, that increasing knowledge of microbes on the one hand and of the operation of DNA on the other, is currently bringing us the mixed but in general momentous benefits of biotechnology. But for true biologists, the real pleasure comes simply from knowing, and from the sense of coming closer to other living things. I am defining 'biologists' broadly: to include naturalists, in the old-fashioned sense, who like simply to observe the old-fashioned, who like simply to observe nature, and scientist, who seek to explain its workings by proposing hypotheses and then testing them out. True biologists seek something more in nature than mere utility. They feel in their bones, and all their sense proclaim, that there is an order among living things; and it is this 'natural' order that they seek to reflect in their classifications. They feel, too, that there should be criteria for classification that are not simply arbitrary, but reflect some real and important affiliations. Thus, what is often called 'natural classification' is based on what biologists construe as the underlying order of nature; or that is the intention. Biologists(broadly defined) have been seeking to devise such a classification at least since the time of the Greek philosopher Aristotle.