考满分 toefl

1 .<-NARRATOR:->Listen to part of a lecture in a botany class.

旁白：请听一段植物学讲座的节选。

1 .<-FEMALE PROFESSOR:->So, continuing with crop domestication, and corn, or, um, maize, as it’s often called. Obviously it’s one of the world’s most important crops today.

教授：我们继续讲作物驯化，玉米—或者说，嗯，我们经常叫它玉米，显然它是现在世界上最重要的作物之一。

2 .It’s such a big part of the diet in so many countries, and it’s got so many different uses, that it’s hard to imagine a world without it.

很多国家的饮食构成中它都占有大比重，它的用途多样，我们很难想象没有玉米的世界。

3 .But because it doesn’t grow naturally, without human cultivation, and because there’s no obvious wild relative of maize…

但因为它不是自然生长的，没有人类的栽培，也因为玉米没有明显的野生近亲。。。

4 .uh, well, for the longest time, researchers weren’t able to find any clear link between maize and other living plants.

嗯，所以很长时间研究者都找不到任何玉米和其他植物的明确联系。

5 .And that’s made it hard for them to trace the history of maize.

这就使得他们很难追溯玉米的历史。

1 .Now, scientific theories about the origins of maize first started coming out in the 1930s.

关于玉米起源的科学理论最早出现在20世纪30年代。

2 .One involved a plant called teosinte.

这个理论涉及到一种叫做大刍草的植物。

1 .Teosinte is a tall grass that grows wild in certain parts of Mexico and Guatemala.

大刍草是一种高高的草，生长在墨西哥和危地马拉的某些地区。

2 .When researchers first started looking at wild teosinte plants, they thought there was a chance that the two plants, um, maize and teosinte, were related.

当研究人员第一次开始观察野生大刍草时，他们认为有可能这两种植物，嗯，玉米和大刍草是相关的。

3 .The young wild teosinte plant looks a lot like the corn plant, and the plants continue to resemble each other, at least superficially, even when they’re developed.

年幼的野生大刍草长得和玉米很像，甚至他们生长发展后，这些植物至少在表面上仍然彼此相似。

4 .But when the scientists examined the fruits of the two plants, it was a different story.

但是当科学家检查这两种植物的果实的时候，出现了很大的不同。

1 .When you look at ripe corn, you see row upon row of juicy kernels… um, all those tiny little yellow squares that people eat.

当你看玉米的时候，你可以看到一串串多汁的谷粒...嗯，就是所有这些人们可以吃的小小的黄色小粒粒。

2 .Fully-grown teosinte, on the other hand, has a skinny stalk that holds only a dozen or so kernels behind a hard, um, almost stonelike casing.

然而完全长成的大刍草，则用薄薄的枝干包裹着仅仅数十粒左右的谷物，谷物外面还套着一层石头一样硬的壳。

3 .In fact, based on the appearance of its fruit, teosinte was initially considered to be a closer relative to rice than to maize.

实际上，根据它谷粒的外观，大刍草一开始是被认为与稻谷的亲缘更近，而不是与玉米。

1 .But there was one geneticist, named George Beadle, who didn’t give up so easily on the idea that teosinte might be… well… the “parent” of corn.

但是有一个遗传学者，叫做George Beadle，他没有轻易放弃大刍草可能是...嗯...是玉米亲属的观点。

1 .While still a student in the 1930s, Beadle actually found that the two plants had very similar chromosomes, very similar genetic information.

在20世纪30年代，当他还是个学生的时候，Beadle实际上发现了这两种植物有非常相似的染色体，非常相似的基因信息。

2 .In fact, he was even able to make fertile hybrids between the two plants.

事实上，他甚至能够在这两种植物之间培育出有繁殖能力的杂交品种。

3 .In hybridization, you remember, the genes of two species of plants are mixed to produce a new, third plant—a hybrid.

在杂交过程中，你要记住，两种植物的基因混合产生了一种新的，第三种植物——杂交品种。

4 .And if this offspring, this hybrid, is fertile, then that suggests that the two species are closely related genetically.

如果这个杂交后代是有繁殖力的，那么这表明这两个物种在基因上是紧密相关的。

5 .This new, hybrid plant looked like an intermediate, right between maize and teosinte.

这种新的杂交植物看起来像一种介于玉米和大刍草之间的中间品种。

6 .So, Beadle concluded that maize must’ve been developed over many years, uh, that it is a domesticated form of teosinte.

所以Beadle得出结论说，玉米必须经过很多年才能培育出来，它是大刍草的驯化形态。

1 .Many experts in the scientific community, however, remained unconvinced by his conclusions.

然而，科学界的许多专家仍然不相信他的结论。

2 .They believed that, with so many apparent differences between the two plants, it would have been unlikely that ancient, that prehistoric peoples could’ve domesticated maize from teosinte.

他们相信，这两种植物之间有那么多的明显的区别，古代的—史前的人们不大可能把大刍草驯化成玉米。

3 .I mean, when you think about it, these people lived in small groups, and they had to be on the move constantly as the seasons changed.

我的意思是，当你仔细想这件事的时候，这些古代人居住在小小的群落里，随着季节变化他们要不停地迁徙。

4 .So for them to selectively breed, to have the patience to be able to pick out just the right plants and gradually over generations, separate out the durable, nutritious maize plant from the brittle teosinte that easily broke apart,

所以对于他们来说，进行选择性培育，耐心地挑出来所有可以继续培育下去的植株，并一代代培育下去，从脆弱的大刍草植株里分离出持久而有营养的玉米植株，

5 .it’s a pretty impressive feat, and you can easily see why so many experts would have been skeptical.

这是一个令人印象深刻的壮举，你可以很容易地看出为什么那么多专家会持怀疑态度。

1 .But, as it turns out, Beadle found even more evidence for his theory when he continued his experiments, producing new hybrids, to investigate the genetic relationship between teosinte and maize.

但是就像结果所说明的那样，Beadle在继续实验的时候发现了甚至更多的支持他的理论的证据，他继续去培育新的杂交植株，来探索大刍草和玉米之间的基因关系。

2 .Through these successive experiments, he calculated that only about five specific genes were responsible for the main differences between teosinte and maize. The plants were otherwise surprisingly similar genetically.

通过这些成功的实验，他计算出只有大约五个基因会导致大刍草和玉米之间的主要差异，而两者其余的基因则表现出了令人惊讶的相似性。

1 .And more recently, botanists have used modern DNA testing to scan plant samples collected from throughout the Western Hemisphere.

最近，植物学家利用现代DNA检测技术扫描了从整个西半球采集的植物样本。

2 .This has allowed them to pinpoint where the domestication of maize most likely took place. And their research took them to a particular river valley in southern Mexico.

这使得他们能够确定玉米驯化最有可能发生在哪里。他们的研究把他们带到墨西哥南部的一个特定河谷。

3 .They’ve also been able to estimate that the domestication of maize most likely occurred about 9,000 years ago.

他们还估计，玉米的驯化最有可能发生在大约9000年前。

4 .And subsequent archaeological digs have confirmed this estimate. In one site, archaeologists uncovered a set of tools that were nearly 9,000 years old.

随后的考古发掘证实了这一估计。在其中一个遗址，考古学家发现了一套距今近9000年的工具。

5 .And these tools were covered with a dusty residue, a residue of maize, as it turns out. Thus making them the oldest physical evidence of maize that we’ve found so far.

这一些工具是被满是灰尘的残渣所覆盖的，这些残渣被发现是玉米的残渣。这就使得它们成为了至今为止我们所发现的最古老的玉米的实物证据。