Almost Like a Whale

Now, fewer than a thousand pandas are left. In China, to kill one means the death penalty. Taxonomists. too, are more careful with their material than once they were. The essence of a species can now be (or so the museum-keepers believe) be preserved not in its bones but in its genes. The Bulo Burti boubou shrike of Somalia was recognized in 1991 on the basis of the DNA sequence in a feather shed by a captive bird. The type specimen - the very substance - of this new form is a set of dark bands on a photographic plate. The rest of the bird was released.

Not all pandas - or Bulo Burti boubou shrikes - are alike. They may look the same but are, like whales, dogs, or viruses, full of diversity. Classifiers hence face a fatal temptation: to split their animals into too many groups. As in the Kennel club or the United Nations, quarrels break out between those who like to subdivide the world and those who hope to unify it.

Amersham Pharmacia Biotech Ltd 1998 DNA fingerprints - can these genetic blueprints define a species?

A rich nineteenth-century collector, Isaac Leigh, was interested in the freshwater mussels of North America. He named more than a thousand kinds on the basis of tiny variations in shell-shape and size. Now the number has been reduced by two-thirds. A hundred and two of his types are classified as one. Isaac Leigh was too enthusiastic about his varieties. His cherished diversity was no more than that between people with brown or blue eyes or between the pink- and yellow-legged herring gulls that once infested Estonian marshes. He had, nevertheless, put his finger on a problem that still plagues museums. How should they fix the frontiers between supposed entities when each is filled with variation?

Genetics, the science of differences, has not made their job any easier. Before it began it had often been asserted - but the assertion was quite incapable of proof - that the amount of variation under nature is strictly limited in quantity. Now, the claim can be tested, and it fails.

Most members of most species do not look much different one from the next. Any fruit-fly is much like another, and even their best friends find it hard to tell mice apart. In spite of some exceptions - the colourful snails or butterflies that come in dozens of forms and are still studied by a few outmoded naturalists - to share a Latin name imposes, almost by definition, a certain uniformity upon those who bear it. That comforts both creationists and experts on taxonomy. They like to see existence as a set of neat ideals, each filled with some pure Platonic essence. However, a great deal is hidden within even the most uniform creature. Genetics shows that no one - not even the glorified chemists which most biologists have become - can any longer suppose that all the individuals of same species are cast in the very same mould.