(postedapril2001)biodiversityseriescontentsintroductionwhy(编辑修改稿)

(postedapril2001)biodiversityseriescontentsintroductionwhy(编辑修改稿)内容摘要：

d simple belonging most urbanites experience with a simple walk in a woodlot, through a meadow, or along a clean shoreline. Yet these three categories of the effects of the living world on human life are absolutely crucial to modern and future human life on pla Earth. UTILITARIAN VALUES OF BIODIVERSITY When asked how many species humans routinely utilize in their daily life, most people (including most professional biologists) say, at most, perhaps one or two hundred. The correct answer is at least 40,000: Globally, each day we depend on over 40,000 species of plants, animals, fungi, and microbes. I am counting here only those species that we are deliberately exploiting. Still others, such as the microbe Escherichia coli, which lives by the millions in our intestines and is absolutely vital for normal digestion, are, fortunately, simply there. Many of us think that food es from the grocery store, and have little idea of its ultimate provenance. If some of us realize that spaghetti es, not from trees but from wheat flour, we still tend to think that the Agricultural Revolution is long since plete, that we have already abstracted from nature all the plant and animal species that we are ever going to farm. We think that whatever improvements in crop yield and disease resistance two critically important factors in the ongoing race to feed the 250,000 extra mouths we are currently adding each day can e strictly from improved breeding techniques, and especially from the seeming magic wrought by the recently developed techniques of biotechnology. Nothing could be farther from the truth. Here, a direct analogy with the natural world is apt: Evolution works through natural selection, the process Darwin (and Alfred Russell Wallace) discovered. On average, the anisms that thrive best will survive and reproduce, passing to their offspring the very traits that allowed them to flourish. Breeders do the same thing, allowing only those sheep, say, that have the woolliest coats to reproduce in the hopes of producing future sheep with even thicker coats than their forerunners had. But selection alone whether natural or artificial will not do the trick. Another ingredient is required: the presence of geic variation. You can only select from an assortment of different traits. Once you have gone as far as you can in selecting from the available range of geic traits, the process, inevitably, es to a halt. The reason why evolution did not stop billions of years ago is that spontaneous geic changes mutations occur each generation, renewing and increasing geic variation. Biotechnology allows us to inject genes directly into domesticated plants and animals. At first glance, it seems that we have coopted nature, once again substituting a clever bit of technology over a chancier and slower natural process. But the genes we insert to produce, say, frostresistant strawberries, have to e from somewhere. You can39。 t just go to a molecular biology facility and ask them to invent a gene that will make strawberry plants hardier. No one has the faintest idea what that gene would be, what its precise instructional coding would be, or where it might be inserted into the chromosomes of the strawberry cells. Biotechnology works the oldfashioned way: One must first find a geic feature that performs the desired function, before it can be extracted, manipulated, and inserted with the marvels of modern biotechnological technique into the stock where you would like to see that desired effect expressed. That means we must find geic variation in the usual place: in nature, in wild versions of domesticated species, and in their nearest relatives. For many crop plants, there is an additional ace in the hole: The centuries, indeed the millennia, that farmers have been patiently tilling the land, sowing seeds, and harvesting crops that are bountiful one year, skimpy the next, have seen the emergence of countless landraces, local varieties of corn, wheat, tomatoes, etc. that seem to do best in a particular bination of local soil and climate. The history of agriculture has itself produced, through simple artificial selection, a vast storehouse of geic variation. All that variation is under serious threat. As science reporter Paul Raeburn recounts in his book The Last Harvest (1995), destruction of ecosystems in the wild threatens to obliterate countless species that are close kin to vital agricultural crops. He tells of the bination of skill, persistence, and luck that has enabled botanists from the United States and Mexico to locate a previously unknown species of wild corn, Zea diploperennis. This rare and rather unprepossessing plant promises to enable agricultural geicists to abstract its genes, which convey resistance to a wide assortment of corn diseases. The alarming coda to an otherwise encouraging story of the importance of natural geic variation in wild species to our collective agricultural effort is that Zea diploperennis almost certainly would have bee extinct within at most a few decades as its limited natural habitat in Mexico39。 s Sierra de Monantlan was suffering precisely the same sort of conversion (for agricultural use!) that we are witnessing around the entire globe. How many other wild relatives of domesticated species have we already lost, and what will the effects of that loss be as we struggle to feed increasing billions of people over the next several decades? Raeburn notes that a similar fate is meeting thousands of landraces. We lose species in the wild as we convert land for agricultural and other uses. We are losing landraces for a different reason: The switch from small singlefamily farming to largescale agribusiness, coupled with recent dramatic advances in biotechnology, means we have begun to plant only a few super varieties of crop pl。