Wednesday, January 13, 2010

Lumping and splitting

In the 11 December issue of Science, Jim Endersby writes about the "lumpers" and "splitters" among early 19th-century biologists. It was a time when naturalists spread out across the globe collecting and classifying plants and animals. The lumpers focussed on broad categories of likeness; the splitters on the almost infinite degrees of difference. Lumpers, like Joseph Hooker, railed against the proliferation of species among the splitters; only by seeking the likenesses of organisms would the underlying laws of biology be revealed, he argued. He favored defining species broadly, submerging many minor varieties under a single name, whereas splitters named varieties as subspecies or even full species.

When Darwin provided the underlying explanation that Hooker sought -- evolution by natural selection -- it became clear that both lumping and splitting had its uses. Writes Endersby: "If every species had been created in its modern form, their boundaries should be clearly defined; but, if each species evolved from another, there ought to be cases where the random variations that characterized all living things had yet to be sifted by natural selection or where extinction had not yet created the gaps that allowed species to be clearly discerned and named."

In Origin of Species, Darwin asserted that "Our classifications will come to be, as far as they can be so made, genealogies."

To some extent, the distinction between lumpers and splitters continues today among biological taxonomists. A creative tension between the general and the particular is at the heart of science. Without the general, there can be no "laws of nature." Without careful attention to the particular, the "general" can only be an airy generalization.

We are all of us, even in our nonscientific lives, lumpers or splitters. Some of us are most excited by the big picture -- politics, ecology, global warming. Others focus on next-door neighbors, the backyard garden, this morning's sunrise. Even within these broad categories we lump and split. We love our fellow humans, for example, but we fall in love with a single individual.

The biggest lump in the human conceptual repertoire, I suppose, is God. The finest split is the subatomic particle. Darwin resolved the lumper/splitter debate of early 19th-century naturalists with the idea of incremental common descent -- taxonomy as geneology. The same might be possible with the memes by which we order our intellectual lives. Our ideas no more came fully formed into the world than did species by special creation. They evolved from beginnings that are lost in the mists of time. Each of us -- intellectually -- is a twig on an evolutionary tree of ideas; we gathered up our conceptual understanding of the world from a well of history that includes both nature and nurture. We lump and split, but our categories are given by our pasts. Even the most creative among us drags our memetic inheritance into the future, as a biological species or individual expresses a historical gathering of genes.