剑桥雅思4阅读Test1Passage2原文翻译

第1自然段

Some of the senses that we and other terrestrial mammals take for granted are either reduced or absent in cetaceans or fail to function well in water. For example, it appears from their brain structure that toothed species are unable to smell. Baleen species, on the other hand, appear to have some related brain structures but it is not known whether these are functional. It has been speculated that, as the blowholes evolved and migrated to the top of the head, the neural pathways serving sense of smell may have been nearly all sacrificed. Similarly, although at least some cetaceans have taste buds, the nerves serving these have degenerated or are rudimentary.

第1自然段

我们和其他陆地哺乳动物所依赖的一些感官，在鲸类身上要么减弱，要么缺失，要么在水中无法正常发挥作用。例如，从它们的脑结构来看，有齿的鲸类物种似乎无法嗅到气味。另一方面，须鲸物种似乎有一些相关的脑结构，但目前尚不清楚它们是否功能正常。有人推测，随着喷气孔的进化和迁移至头部顶部，用于嗅觉的神经通路可能几乎全部丧失。类似地，虽然至少某些鲸类拥有味蕾，但服务于味觉的神经已经退化或发育不全。

第2自然段

The sense of touch has sometimes been described as weak too, but this view is probably mistaken. Trainers of captive dolphins and small whales often remark on their animals’ responsiveness to being touched or rubbed, and both captive and free-ranging cetacean individuals of all species (particularly adults and calves, or members of the same subgroup) appear to make frequent contact. This contact may help to maintain order within a group, and stroking or touching are part of the courtship ritual in most species. The area around the blowhole is also particularly sensitive and captive animals often object strongly to being touched there.

第2自然段

触觉有时被描述为较弱，但这种观点可能是错误的。圈养海豚和小型鲸类的训练员经常提到它们对于被触摸或被搓揉的反应，而所有物种的圈养和自由游动的鲸类个体（尤其是成年个体、幼仔或同一子群成员）似乎经常接触彼此。这种接触可能有助于维持群体内的秩序，而抚摸或触摸也是大多数物种求偶仪式的一部分。喷气孔周围的区域特别敏感，圈养动物经常强烈反对在那里被触摸。

第3自然段

The sense of vision is developed to different degrees in different species. Baleen species studied at close quarters underwater – specifically a grey whale calf in captivity for a year, and free-ranging right whales and humpback whales studied and filmed off Argentina and Hawaii – have obviously tracked objects with vision underwater, and they can apparently see moderately well both in water and in air. However, the position of the eyes so restricts the field of vision in baleen whales that they probably do not have stereoscopic vision.

第3自然段

视觉的发展程度因不同物种而异。近距离在水下研究过的须鲸物种，比如一只在圈养环境中生活了一年的灰鲸幼仔，以及在阿根廷和夏威夷附近进行研究和拍摄的自由游动的北极鲸和座头鲸，它们明显能够在水下跟踪物体，并且似乎在水中和在空中都有较好的视力。然而，须鲸眼的位置限制了视野范围，它们可能没有立体视觉。

第4自然段

On the other hand, the position of the eyes in most dolphins and porpoises suggests that they have stereoscopic vision forward and downward. Eye position in freshwater dolphins, which often swim on their side or upside down while feeding, suggests that what vision they have is stereoscopic forward and upward. By comparison, the bottlenose dolphin has extremely keen vision in water. Judging from the way it watches and tracks airborne flying fish, it can apparently see fairly well through the air-water interface as well. And although preliminary experimental evidence suggests that their in-air vision is poor, the accuracy with which dolphins leap high to take small fish out of a trainer’s hand provides anecdotal evidence to the contrary.

第4自然段

另一方面，大多数海豚和鼠海豚的眼睛位置表明它们具有前向和向下的立体视觉。淡水海豚的眼睛位置提示它们的视觉主要是前向和向上的立体视觉，因为它们在觅食时经常侧身或倒挂。相比之下，虎鲸在水中具有非常敏锐的视力。从它们观察和追踪空中飞鱼的方式来看，它们似乎也能够相当好地通过水面观察。虽然初步实验证据表明它们在空气中的视力较差，但是海豚高高跃起从训练员手中夺取小鱼的准确性提供了反面证据。

第5自然段

Such variation can no doubt be explained with reference to the habitats in which individual species have developed. For example, vision is obviously more useful to species inhabiting clear open waters than to those living in turbid rivers and flooded plains. The South American boutu and Chinese beiji, for instance, appear to have very limited vision, and the Indian susus are blind, their eyes reduced to slits that probably allow them to sense only the direction and intensity of light.

第5自然段

这种变异无疑可以通过个体物种所生活的栖息地来解释。例如，对于栖息在清澈开阔水域中的物种来说，视觉显然更加有用，而对于生活在浑浊河流和洪水平原中的物种来说，视觉则不那么重要。例如南美洲的boutu和中国的beiji，它们的视觉似乎非常有限，而印度的susus是盲目的，它们的眼睛只有缝隙，可能只能感知光的方向和强度。

第6自然段

Although the senses of taste and smell appear to have deteriorated, and vision in water appears to be uncertain, such weaknesses are more than compensated for by cetaceans’ well-developed acoustic sense. Most species are highly vocal, although they vary in the range of sounds they produce, and many forage for food using echolocation1. Large baleen whales primarily use the lower frequencies and are often limited in their repertoire. Notable exceptions are the nearly song-like choruses of bowhead whales in summer and the complex, haunting utterances of the humpback whales. Toothed species in general employ more of the frequency spectrum, and produce a wider variety of sounds, than baleen species (though the sperm whale apparently produces a monotonous series of high-energy clicks and little else). Some of the more complicated sounds are clearly communicative, although what role they may play in the social life and ‘culture’ of cetaceans has been more the subject of wild speculation than of solid science.

第6自然段

尽管味觉和嗅觉似乎已经退化，水中视觉似乎不确定，但这些弱点都被鲸类发达的听觉所弥补。大多数物种都具有高度发声能力，虽然它们在产生声音的范围上存在差异，并且许多物种使用回声定位来觅食。大型须鲸主要使用较低的频率，并且在音色上通常受到限制。值得注意的例外是夏季北极座头鲸几乎像歌曲一样的合唱和座头鲸发出复杂而令人陶醉的声音。相比之下，总体而言，有齿的物种在频谱上应用更多，并且产生更多种类的声音，而须鲸物种则不同（虽然抹香鲸似乎只产生单调的一系列高能量的点击声）。一些更复杂的声音显然具有信息传递的功能，尽管它们在鲸类的社交生活和“文化”中起到什么作用，目前更多地是凭借狂野的猜测而不是扎实的科学依据。