I Have Landed (53 page)

But not all “weed” species can be called “exotic” in the sense of being artificially imported from other geographic areas. Weeds must often be classified as indigenous, even though their geographic ranges tend to be large, and their means of natural transport efficient and well developed.

The evolutionary fallacy in equating native with optimally adapted can be explicated most clearly by specifying the central theme of natural selection as a causal principle. As Darwin recognized, and stated so forcefully, natural selection generates adaptation to changing local environments—and nothing else. The Darwinian mechanism includes no concept of general progress or universal betterment. The “struggle for existence” can only yield local appropriateness. Moreover, and even more important for debates about superiority of native plants, natural selection is only a “better than” principle, not an optimizing device. That is, natural selection can only transcend the local standard and cannot work toward universal “improvement”—for once a species prevails over others at a location, no pressure of natural selection need arise to promote further adaptation. (Competition within species will continue to eliminate truly defective individuals and may promote some refinement by selection of fortuitous variants with still more advantageous traits, but the great majority of successful species are highly stable in form and behavior over long periods of geological time.)

For this reason, many native plants, evolved by natural selection as adaptive to their regions, fare poorly against introduced species that never experienced the local habitat. If natural selection produced optimality, this very common situation could never arise, for native forms would prevail in any competition against intruders. But most Australian marsupials succumb to placentals imported from other continents, despite tens of millions of years of isolation—surely more than enough time for Australian natives to attain irreplaceable incumbency, if natural selection generated optimality. And
Homo sapiens
, after arising in Africa, seems able to prevail in any exotic bit of real estate, almost anywhere in the world!

Thus the primary rationale so often stated for preferring native plants—that, as locally evolved, such species must be best adapted—cannot be sustained. I strongly suspect that a large majority of well-adapted natives could be supplanted by some exotic form that has never experienced the immediate habitat. In Darwinian terms, this exotic would be better adapted than the native—though we may well, on defensible aesthetic or even ethical grounds, prefer the natives (for nature's factuality can never enjoin our moral decisions).

We should, I think, grant the legitimacy of only one limited point from evolutionary biology on the subject of adaptation in native plants. At least we
do
know
that well-established natives must be adequately adapted, and we can observe their empirical balances with other local species. We
cannot know
what an exotic species will do—and we can all cite numerous, and tragic, stories of exotics imported for a restricted and benevolent reason that then grew like kudzu to everyone's disgust and detriment. We also know that natives grow appropriately—though not necessarily optimally—in their environment, while exotics may not fit without massive human “reconstruction” of habitat, an intervention that many ecologically minded people deplore. I confess that nothing strikes me as more vulgar or inappropriate than a bright green lawn in front of a mansion in the Arizona desert, an artificial construction sucking up precious water that already must be imported from elsewhere. A preference for natives does foster humility and does counteract human arrogance—for such preference does provide the only sure protection against our profound ignorance of potential consequences when we import exotics. But the standard argument—that natives should be preferred as best adapted—must be firmly rejected as simply false within Darwinian theory.

This second argument, harder to formulate and less clearly linked to a Darwinian postulate, somehow seems even more deeply embedded (as a fallacy) into conventional arguments for preferring native plants. This argument holds that plants occupy their natural geographic ranges for reasons of maximal appropriateness. Why, after all, would a plant live only in a particular region of five hundred square kilometers unless this domain constituted its “natural” home—the place where this species, and no other, fits best? Smyser, for example, writes: “In any area there is always a type of vegetation that would exist without being planted or protected. This native vegetation consists of specific groups of plants that adapted to specific environmental conditions.” But the deepest principle of evolutionary biology—the construction of all current biological phenomena as outcomes of contingent history, rather than optimally manufactured situations—exposes this belief as nonsense.

Organisms do not necessarily, or even generally, inhabit the geographic area best suited to their attributes. Since organisms (and their areas of habitation) originate as products of a history laced with chaos, contingency, and genuine randomness, current patterns (although obviously workable) will rarely express anything close to an optimum, or even a “best possible on this earth now”—
whereas the pre-Darwinian theory of natural theology, with direct creation of best solutions, and no appreciable history thereafter (or ever), could have validated an idea of native as best. Consequently, although native plants must be adequate for their environments, evolutionary theory grants us no license for viewing natives as the best-adapted inhabitants conceivable, or even as the best available among all species on the planet.

An enormous literature in evolutionary biology documents the various, and often peculiar, mechanisms whereby organisms achieve fortuitous transport as species spread to regions beyond their initial point of origin. Darwin himself took particular interest in this subject. During the 1850s, in the years just before publication of the
Origin of Species
in 1859, he wrote several papers on the survival of seeds in salt water. (How long could seeds float without sinking? Would they still germinate after such a long bath?) He determined that many seeds could survive long enough to reach distant continents by floating across oceans—and that patterns of colonization therefore reflected historical accidents of available pathways, and not a set of optimal environments.

Darwin then studied a large range of “rarely efficient” means of transport beyond simple carriage by waves—natural rafts of intertwined logs (often found floating in the ocean hundreds of miles from river mouths), mud caked on birds' feet, residence in the gut of birds with later passage in feces. In his usually thorough and obsessive way, Darwin assiduously collected information and found more than enough means of fortuitous transport. He wrote to a sailor who had been shipwrecked on Kerguelen Island to find out if he remembered any seeds or plants growing from driftwood on the beach. He asked an inhabitant of Hudson Bay if seeds might be carried on ice floes. He studied the contents of ducks' stomachs. He received, in the mail and with delight, a pair of partridges' feet caked with mud; he rooted through bird droppings. He even followed a suggestion of his eight-year-old son that they float a dead and well-fed bird. Darwin wrote, in a letter, that “a pigeon has floated for thirty days in salt water with seeds in crop and they have grown splendidly.” In the end, Darwin found more than enough mechanisms to move viable seeds.

“Natives,” in short, are the species that happened to find their way (or evolve
in situ
), not the best conceivable species for a spot. As in my first argument about adaptation, the proof that current incumbency as “native” does not imply superiority against potential competitors exists in abundance among hundreds of imported interlopers that have displaced natives throughout the world—eucalypts in California, kudzu in the American Southeast, rabbits and other placental mammals in Australia, and humans just about everywhere.

“Native” species can only be defined as those forms that first happened to
gain and keep a footing. We rightly decry the elitist and parochial claims of American northeastern WASPs to the title of native. But, however “politically incorrect” the point, the fashionable status of “Indians” (so called by Columbus's error) as “Native Americans” makes just as little sense in biological terms. “Native Americans” arrived in a geological yesterday, some twenty thousand years ago (perhaps a bit earlier), probably on the geographic fortuity of a pathway across the Bering Strait, perhaps by some equivalent of
Kon-Tiki
. The first Americans were no more intrinsically suited than any other people to New World real estate. They just happened to arrive first.

In this context, the only conceivable rationale for the moral or practical superiority of “natives” (read first-comers) must lie in a romanticized notion that old inhabitants learn to live in ecological harmony with surroundings, while later interlopers tend to become exploiters. But this notion, however popular among “new agers,” must be dismissed as romantic drivel. People are people, whatever their technological status; some learn to live harmoniously for their own good—and others don't, to their own detriment or destruction. Preindustrial people have been just as rapacious (though not so quickly, perhaps, for lack of tools) as the worst modern clearcutters. The Maori people of New Zealand wiped out a rich fauna of some twenty moa (giant bird) species within a few hundred years. The “native” Polynesians of Easter Island wiped out everything edible or usable (and, in the end, could find no more logs to build boats or to raise their famous statues), and finally turned to self-destruction.

In summary of my entire argument from evolutionary theory, “native” plants cannot be deemed biologically best in any justifiable way. “Natives” are only the plants that happened to arrive first and be able to flourish (the evolutionary argument based on geography and history)—while their capacity for flourishing only indicates a status as “better than” others available, not as optimal or globally “best suited” (the evolutionary argument based on adaptation and natural selection).

Speaking biologically, the only general defense that I can concoct for native plants lies in protection thus afforded against our overweening arrogance. At least we know what natives will do in an unchanged environment—for they have generally inhabited an area for a long time, and have therefore stabilized and adapted. We never know for sure what an imported interloper will do—and our consciously planted exotics have “escaped” to disastrous spread and extirpation of natives (the kudzu model) as often as they have supplied the intended horticultural or agricultural benefits.

As a final ethical point (and I raise this issue as a concerned human being,
not as a scientist, for my profession can offer no direct moral insight), I do understand the appeal of the ethical argument that we should leave nature alone and preserve as much as we can of the life that existed and developed before our very recent geological appearance. Like all evolutionary biologists, I treasure nature's bounteous diversity of species (the thought of half a million described species of beetles—and so many more, yet undescribed—fills me with an awe I can only call reverent). And I do understand that much of this variety lies in geographic diversity (different organisms evolved in similar habitats in many places on our planet, as a result of limits and accidents of access). I would certainly be horrified to watch the botanical equivalent of McDonald's uniform architecture and cuisine wiping out every local diner in America. Cherishing native plants does allow us to defend and preserve a maximal amount of local variety.

But we must also acknowledge that the argument for strict “nativism” has an ethical downside inherent in the notion that “natural” must be right and best—for such an attitude easily slides from the philistinism of denying any role to human intelligence and good taste, thence to the foolish romanticism of viewing all that humans might accomplish in nature as “bad” (and how then must we judge Olmsted's Central Park), and even, in an ugly perversion—but realized in our time by Nazi invocation of nativist doctrine—to the claim that my “native” is best, and yours fit only for extirpation.

The best defense against all these misuses, from mild to virulent, lies in a profoundly humanistic notion as old as Plato—one that we often advance in sheepish apology, but should rather honor and cherish: the idea that “art” should be defined as the caring, tasteful, and intelligent
modification
of nature for respectful human utility. If we can practice this art in partnership with nature, rather than by exploitation (and if we also set aside large areas for rigidly minimal disturbance, so that we never forget, and may continue to enjoy, what nature accomplished during nearly all of her history without us), then we may achieve optimal balance.

People of goodwill may differ on the best botanical way to capture the “spirit of democracy”—from one end of maximal “respect” for nature by using only her unadorned and locally indigenous (“native”) products, to the other of maximal use of human intelligence and aesthetic feeling in sensitive and “respectful” mixing of natives and exotics, just as our human populations have so benefited from imported diversity. Jens Jensen extolled the first view: