填空题
Farm-raised pigs are dirty, smelly animals that get no
respect. They’re also an environmental hazard. Their manure contains phosphorus,
which, when it rains, runs off into lakes and estuaries, depleting oxygen,
killing fish, stimulating algae overgrowth and emitting greenhouse
gases.
41. ______. Pigs provide more dietary protein, more
cheaply, to more people than any other animal. Northern Europe still maintains
the highest pig-to-human ratio in the world (2-1 in Den- mark), but East Asia is
catching up. During the 1990s, pork production doubled in Vietnam and grew by 70
percent in China— along densely populated coastlines, pig density exceeds 100
animals per square kilometer. The resulting pollution is “threatening fragile
coastal marine habitats including mangroves, coral reefs and sea grasses,”
according to a report released in February by the Food and Agriculture
Organization of the United Nations.
As it turns out, there is a
solution to the pig problem, but it requires a change of mind-set among
environmentalists and the public. 42. ______.
The Enviropig is
one of many new technologies that are putting environmentalists and organic-food
proponents in a quandary: should they remain categorically opposed to
genetically modified (GM) foods even at the expense of the environment? 43.
______. The most significant GM applications will be ones that help alleviate
the problem of agriculture, which accounts for 38 percent of the world’s
landmass and is crowding out natural ecosystems and species habitats. GM crops
that can be produced more efficiently would allow us to return land to
nature.
44. ______. U.S. Department of Agriculture scientist
Eliot Herman has already created a less-allergenic soybean — an important crop
for baby foods. Through genetic surgery, Herman turned off the soy gene
responsible for 65 percent of allergic reactions. Not only was the modified soy
less allergenic in tests but, as Herman explained, “the yield looks perfectly
normal, plants develop and grow at a normal rate and they seem to have the same
kinds of protein, oil and other good stuff in them.” Other scientists have
reported promising results in shutting off allergy-causing genes in peanuts and
shrimp. Should these advances be turned into products, organic soy or peanut
products will be certifiably more dangerous to human health than comparable
nonorganic products.
45. ______. In this climate, much of the needed research
isn’t being pursued. Chances are, farmers will continue to grow their polluting
organic pork, their allergenic organic soy and their neurotoxin-sprayed organic
apples. Worse still, they will make sure that no one else gets a choice in the
matter of improving the conditions of life on earth — unless, that is, others
rise up and demand an alternative.
[A] Two Canadian scientists
have created a pig whose manure doesn’t contain very much phosphorus at all. If
this variety of pig were adopted widely, it could greatly reduce a major source
of pollution. But the Enviropig, as they call it, is the product of genetic
modification — which is anathema to many Westerners.
[B] In
fact, although all commonly used pesticides dissipate so quickly that they pose
a miniscule health risk to consumers, allergic food reactions to natural
products kill hundreds of children each year. Genetically modified foods could
greatly reduce this risk.
[C] Canadian biologists Cecil
Forsberg and John Phillips, for instance, have constructed a novel DNA molecule
that, when planted in a pig embryo, imbues the Enviropig with the ability to
secrete a phosphorus extracting enzyme in its saliva. The results so far are
dramatic — the new pigs can extract all the phosphorus they need from grain
alone, without the phosphorus supplements that farmers now use. This reduces the
phosphorus content of their manure by up to 75 percent.
[D]
Doing away with the pig is not an option.
[E] Pigs can also be
modified to digest grasses and hay (as cows and sheep do), reducing the
energy-intensive use of corn as pig feed. Elsewhere, trees grown for paper could
be made amenable to much more efficient processing, reducing both energy usage
and toxic chemical bleach in effluents from paper mills.
[F] Of
course, stringent testing is needed to show that a genetic modification works
and that the product is not harmful to humans. Scientists can do both of these
things with techniques that allow them to examine and compare the structure and
activity of every one of an animal’s genes.
[G] Unfortunately,
this won’t happen any time soon. Because no society has ever banned allergenic
foods, conventional farmers have no incentive to plant reduced-allergy seeds.
And many members of the public have been led to believe that all genetic
modifications create health risks.