Stephen Spotte’s Scientific Word Of The Week: Species

Stephen Spotte’s Scientific Word Of The Week: Species

Stephen Spotte is a marine scientist and writer. He has published 19 books, including four volumes of fiction, a memoir, and a work of cultural theory. He is a Certified Wildlife Biologist of The Wildlife Society and also holds a U.S. Merchant Marine officer’s license. His popular articles about the sea have appeared in National Wildlife, On the Sound, Animal Kingdom, Explorers Journal, and Science Digest. As a life-long researcher, Stephen holds a soft spot for the possibilities of science’s astonishing unrealities to be mined and their contents allowed to metamorphose into strange shapes and patterns in his fiction writing.

species (noun)

The domestic pekin duck and wild mallard are the same species.

A group of living organisms consisting of similar individuals capable of
exchanging genes or interbreeding. The species is the principal natural
taxonomic unit, ranking below a genus and denoted by a Latin binomial,
e.g. Homo sapiens.

According to Heraclitus, no one can step into the same river twice, suggesting that the natural world is dynamic, forever in flux. By the time you’ve lifted one foot and set it down again the river has changed, and the water where your foot was formerly planted has since passed downstream. Heraclitus’ logic, despite being unassailable, was ignored by later Christian dogma, which stuck to the notion of the world’s creation in less than a week and Earth and its life-forms being immutable. The dinosaur bones were easily explained. Those were remains of creatures uninvited onto Noah’s Ark; they had drowned in the Great Flood.

In the mid-nineteenth century along came Darwin, who in confirming the mutability of life overturned the notion of stasis. Many of his observations seem obvious today. Take the case of domestic animals, molded by humankind, through what might be called “unnatural selection.” Among the results have been meaty ducks and chickens, sheep with thicker wool than wild sheep, and muscular beef cattle seemingly proportioned to hang conveniently in meat lockers.

Darwin argued convincingly that these same processes occur in nature through what he termed “natural selection,” illuminating how a pekin duck—purely domestic, unnaturally heavy, white, and flightless—is genetically a wild mallard. If a pekin and a mallard of different sexes are left alone and their offspring permitted to mate, within a few generations the lineage regresses back to the mallard ancestral form.

The human brain has adapted in part to categorize the world, the better to organize information and objects by pattern for easier recognition. Early anthropologists studying primitive cultures were often amazed when their subjects recognized the same traits and patterns in animals and plants as expert biologists from “advanced cultures,” believing this finding reinforced their conviction that species distinctions are indeed “real” and not simply arbitrary breaks in the chain of life. Such thinking was flawed. What it actually demonstrates is the similarity of human cognition across cultures.

The great categorizer of life was Carl Linnaeus, an eighteenth-century Swedish botanist, zoologist, and physician who devised a simplified system of classifying organisms. His taxonomy comprises seven taxa: kingdom, phylum, class, order, family, genus, and species. From the top down each category engulfs the one below, culminating in a binomial species designation (i.e. the combining of two names, genus and species) such as Homo sapiens.

The Linnaean system greatly streamlined the task of classification but created other difficulties still unsolved, in particular what’s known as the “species problem.” The species designation at the very bottom of the hierarchy is where taxonomy’s rubber meets philosophy’s road of reality, and from Linnaeus until now biology has been confronted by a dilemma of what, exactly, makes a species. Laypersons believe that we scientists know. After all, what’s the purpose of learning all those Latin names if they have no grounding in fact? But we really don’t know. Assuming the animals and plants are real the “species problem” arises when we sort, classify, and give them names. Why? Because the categories we invent are by definition human artifacts, and by extension so are the names we assign as part of the framework devised to explain similarity and relatedness.

Conservationists talk endlessly about the importance of saving species, but what does this mean? The foundations of genetics were unknown in Darwin’s time. He and others recognized certain characters as heritable, but mechanisms of heritability had yet to be discovered. Terms like “gene” and “chromosome” were for future dictionaries, and the chemical structure of DNA wouldn’t be revealed until nearly a century after Darwin published his earthshaking On the Origin of Species.

If life is indeed mutable and exists along a continuum as Darwin proposed, how could it be divisible? How was dividing it into segments called “species” even possible without stopping the flow of the river long enough to step into it and classify what could be observed? Some philosophers of science have argued that Darwin’s notion of “fitness” (the capacity to reproduce), a cornerstone in his theory of natural selection, is redundant, a tautology. Look around, they say. How could every extant species not be the fittest of its kind by definition? Were this not true then like the dinosaurs they should be extinct.

Darwin considered such discussions ridiculous, just fruitless attempts to “define the undefinable.” Taxonomy in his view was simply a convenient means of classification, and he declared a species to be whatever a competent taxonomist said it was. That, more or less, is where things stand after nearly 160 years of discussion and bickering. Even genetics—the ultimate arbiter of relatedness—have done little to refute Darwin’s skepticism.

With the advent of modern genetic techniques we understand that organisms designated as species aren’t necessarily distinct from others especially if closely related groups are compared. This is evident in “subspecies,” which often look different but have the same, or nearly the same, genetic composition as the species or other subspecies with which they’re compared. Take the North American puma (also called cougar), which at one time was partitioned into 15 subspecies based on minor regional and morphological differences. Later genetic testing found their microsatellites (markers used to measure genetic variation) nearly identical, and North America is thus home to just one species of cougar.

Despite regional differences, all North American pumas (or cougars) are a single species.

Whether the basis used to describe a previously unknown organism is morphology, genetics, or (rarely) behavior, whoever designates it as sufficiently unique to deserve its own binomial makes this decision arbitrarily. Nature’s lineage isn’t easily “separated at the joints,” as some might think. In a true continuum do such joints even exist? No rules clarify the boundaries of “speciesism” for the obvious and basic reason that scientists can’t agree about what constitutes a “species.” At last count at least 26 solutions to the “species problem” have been proposed, most of them since Darwin’s time, and none is accepted universally.

At the conservation level we ought to abandon any idea of saving something we can’t define and switch the objective to saving “genetic diversity.” A species name is arbitrary, bestowed like our own given names. Counting the number of “species” inhabiting a particular region of Earth as a conservation baseline isn’t especially useful and inevitably incomplete. Microorganisms, for instance, encompass the bulk of Earth’s genetic diversity. With a few exceptions they remain unidentified and their functions incompletely understood, but their importance in nature’s balance is immeasurable. To be certain our efforts genuinely include all possible genetic diversity we must strive to conserve entire ecosystems and not simply the relatively few organisms we think we can recognize and name.

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