Taxonomy in an age of transformation.
Every plant and animal has a mitochondrial cytochrome oxidase I gene, and its sequence helps researchers assign that plant or animal to a given species, with some degree of certainty. The precise degree of the certainty obtained using this 'barcode' sequence is a matter of some debate, but such sequences are clearly useful to both taxonomists and those who use applied taxonomy. And the industrial-scale sequencing that allowed Craig Venter's ocean-metagenomics consortium to deposit billions of letters of sequence from hundreds of thousands of microbe genes into the GenBank database this week opens up even more possibilities.
The ability to peer into living things and inspect the evolutionary scorecard encoded in their genes has transformed the whole of biology, but few fields have had their core assumptions challenged as deeply as taxonomy. From the time of Carl Linnaeus, born 300 years ago this May, taxonomy has relied on the observation and comparison of physical forms. Now it is supplemented by access to what would once have been seen not as form, but as essence.
Linnaeus himself sought a universal classification of all creation, animal, vegetable and mineral. His categorizations were not uniformly valuable, but his systematic spirit, his stress on the concept of species, and the formal but adaptable conventions of nomenclature he introduced have endured. Nature is glad to celebrate his legacy in this special issue.
DNA sequencing is a gift that Linnaeus would surely have made great use of, but it brings its own problems. It is not always easily reconciled with the careful description, annotation and curation that have been the duty and delight of the taxonomists who carried the linnaean programme forward. The availability of DNA sequences invites both pure scientists (see page 247) and conservationists in the field (see page 250) to change their ways of working.
The classical world in which Linnaeus worked may seem, at first glance, to contrast with our present age of change. Linnaeus believed in fixed species of knowable number created by God and observable by men, in a world more like the lawns and flowerbeds of a formal garden than Darwin's dynamic “tangled bank”.
Yet Linnaeus's classification was itself a response to a changing world — a world in which Europe's growing hegemony was bringing new species into the realm at headlong speed. Linnaeus's own experience of it was bounded by France to the south and Lapland to the north, but the 'apostles' who carried forth his words and sent back samples and descriptions sailed out from Sweden to Arabia, the Americas north and south, China, Japan and the Pacific. Two sailed with Captain Cook, sending back samples from the parts of the Pacific now being sieved for genes.
The various inventories that Linnaeus produced grew ever longer. But while today's world continues to expand in many ways, in some, including those most important to taxonomy, it is shrinking. The creationist Linnaeus was able to assert that “we can count as many species now as were created at the beginning”, but today's taxonomists suspect with near certainty that species are being irretrievably lost to science at an ever-quickening rate.
This whittling away of the bark and marrow of life is not necessarily, in itself, catastrophic. Not every lost species represents a depletion of ecosystem services or other human amenity, and although that is not the only yardstick by which to measure such things, it is in some ways the most important.
Linnaeus would no doubt find much to admire in today's scientific world: its scholarship; its ability to assemble data from around the world in minutes; its tools for examining essences. He would hopefully come round to evolutionary theory — and see the error of the racial categorizations he applied to humans.
The fact that so much of life can be seen in a few buckets of sea water might reconcile him to the fact that swallows do not, as he insisted, wait out the winter in lake-bottom mud. But the realization that the second edition of his dreamed-of universal catalogue would be slimmer than its first would surely strike him as a melancholy one.