托福TPO20阅读和听力文本
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Genetically modification, a process used to change an organism’s genes and hence its characteristics, is now being used to improve trees. Through genetic modification, it is possible to create trees that produce more fruits, grow faster, or withstand adverse conditions. Planting genetically modified trees on a large scale promises to bring a number of benefits.
Firstly, genetically modified trees are designed to be harder than nature trees; that it, they are more likely to survive than their unmodified counterparts. In Hawaii, for example, a new pest-resistant species of papaya tree has been developed in response to ringspot virus infections that have repeatedly damaged the native papaya-tree population. Planting the genetically modified papayas has largely put an end to the ringspot problem.
Moreover, genetically modified trees promise to bring a number of economic benefits to those who grow them. Genetically modified trees tend to grow faster, give greater yields-of food, fruit, or other products-and be hardier. This allows tree farmers to get faster and greater returns on their farming investment and save on pesticides as well.
Finally, the use of genetically modified trees can prevent overexploitation of wild trees. Because of the growing demand for firewood or building timber, many forests around the world are being cut down faster than they can be replaced. Introducing genetically modified trees-designed for fast growth and high yield in given geographic conditions-would satisfy the demand for wood in many of those areas and save the endangered native trees, which often include unique or rare species.
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Sure, there are some benefits of planting genetically modified trees, but are these trees really as great as they first sound? When you examine the subjects closely, here are some serious problems and costs associated with using genetically modified trees.
Firstly, genetically modified trees may be resistant to one particular condition, but that does not necessarily ensure their survival. You see, a typical non-modified tree population is genetically diverse. That means, that for most threatening conditions, for climates, insects and other pests, whatever, there will be at least some individual trees or any given species of trees that are resisted. So even if most of one kind of tree are killed, those few resisted ones will survive and ensure the survival of that species of tree. But genetically modified trees are genetically much more uniformed, so if they are exposed to an environmental challenge they have not been designed for, they will all die. So if the climate changes or a new pest invades the area, the genetically modified trees will likely be completely wiped out.
Now as the second point, there are hidden costs associated with growing genetically modified trees. You see, the companies that genetically modified the trees tend to charge farmers much more for each seed than unmodified tree seeds would cost. Also, as you’ve grown the tree, you cannot collect the seeds and plant a new tree for free. By law, you have to pay the company every time you plant.
And finally, genetically modified trees might actually cause even more damage to the local wild trees. You see, genetically modified trees are often grown more aggressively than natural trees do. And genetically modified trees are typically planted among natural trees. As a result, the genetically modified trees outcompete the native trees for resources: sunlight, soil, nutrients and water, eventually crowding out the natural trees.
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