Title：Sociality in Animals

　　Social insects represent the high point of invertebrate evolution. Some specieslive in communities of millions, coordinating their building and foraging, their reproduction, and their offspring care. Yet sociality is found in only a few species of insects, and is rare among vertebrates as well: wildebeest (large antelope)and lions are the exception rather than the rule. Nearly all fish, amphibians, reptiles, birds, and mammals are solitary, except when courting and mating. Birds and mammals usually rear their young, but year-round family groups are almost unknown, though they are intensely studied where they do exist. The same is true for insects.

　　We know, or think we know, that social groups are good. Wolves are better predators when they hunt in packs, and pigeons escape from falcons far more often when feeding in flocks. Group building projects—the dams beavers build to block a body of water that provides them with relative safety from predators and the lodges they build for shelter, for instance—can provide a high level of protection and comfort. Why, then, are social species so very rare? In fact, living socially presents inevitable problems that transcend habitat needs so that only when these costs are offset by corresponding benefits is group living a plus.

　　The most obvious cost is competition. All the members of a species share the same habitat; when they live together, they are trying to eat the same food and occupy the same nesting sites. In general, there is far less competition away from a group, and selection should favor any individual who (all things being equal) sets off on its own, leaving the members of its group behind to compete among themselves for limited resources. Another difficulty is that concentrations of individuals facilitate disease and parasite transmission. On the whole, social animals carry more parasites and species-specific diseases than do solitary animals. Parasites and diseases diminish the strength and limit the growth of animals, and among highly social creatures, epidemics can devastate whole populations. Distemper (a viral disease) has been known to wipe out entire colonies of seals, for instance. So the penalty of social life is potentially huge.

　　But in some instances, the payoffs can be even greater. Two have already been mentioned: cooperative hunting and defensive groups. Social hunting is likely to evolve where prey is too large to be taken by individuals operating alone. To capture wildebeest some members of a group of lions follow their prey and herd them toward others lying in ambush. In other species, individuals forage or hunt simultaneously and share the food. Vampire bats that have had a bad day, for instance, are fed by more successful members of the community, but they are expected to return the favor in the future. Cooperation can even involve sharing information about the location of food. Some colonial birds, such as bank swallows, use the departure direction of a successful forager (food hunter) to locate concentrations of prey. Information transfer can be unintentional though some species make use of special assembly calls or behavior.

　　Cooperation in group defense, such as we see in circles of musk oxen or elephants, is quite rare among vertebrates but is prevalent among the social insects. The strategy of employing many eyes to watch for danger, on the other hand, is widespread in birds and mammals. A herd of gazelles (small antelope) is far more likely to spot a lurking lion or a concealed cheetah than is a lone individual, and at a greater distance. In fact, a group enters into a kind of time-sharing arrangement in which individual antelope alternate biting off a mouthful of grass with a period of erect and watchful chewing. A larger group can afford more bites per individual per minute, there being more eyes to scan for danger. For a small antelope living in a forest where visibility is limited, however, remaining hidden is probably a better bet than assembling into noisyherds.

　　Among the millions of species of insects, only a few thousand are social. Those rarities are generally confined to termites and Hymenoptera. All termites are social: their diet (cellulose) requires that each generation feed a special kind of bacteria or fungi to the next generation to aid in its digestion. Of the numerous hymenopterans, some are social—including all ants and a few bees and wasps—but many are solitary

　　Paragraph 1

　　Social insects represent the high point of invertebrate evolution. Some specieslive in communities of millions, coordinating their building and foraging, their reproduction, and their offspring care. Yet sociality is found in only a few species of insects, and is rare among vertebrates as well: wildebeest (large antelope)and lions are the exception rather than the rule. Nearly all fish, amphibians, reptiles, birds, and mammals are solitary, except when courting and mating. Birds and mammals usually rear their young, but year-round family groups are almost unknown, though they are intensely studied where they do exist. The same is true for insects.

　　1. According to paragraph 1, which of the following is true of sociality among animal species?

　　 Sociality is much more common among invertebrates than among vertebrates.

　　 Very few animals are considered social because most spend the majority of their lives alone.

　　 An animal group must contain more than one family unit for the species tobe considered social.

　　 All animals that rear their young are considered to be social.

　　Paragraph 2

　　We know, or think we know, that social groups are good. Wolves are better predators when they hunt in packs, and pigeons escape from falcons far more often when feeding in flocks. Group building projects—the dams beavers build to block a body of water that provides them with relative safety from predators and the lodges they build for shelter, for instance—can provide a high level of protection and comfort. Why, then, are social species so very rare? In fact, living socially presents inevitable problems that transcend habitat needs so that only when these costs are offset by corresponding benefits is group living a plus.

　　2. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

　　 Group living allows some animals to transcend problems of habitat.

　　 Group living is only advantageous when benefits outweigh inevitable problems.

　　 Problems resulting from living socially extend beyond the habitat.

　　 It is difficult to determine whether the benefits of social living offset its costs

　　Paragraph 3

　　The most obvious cost is competition. All the members of a species share the same habitat; when they live together, they are trying to eat the same food and occupy the same nesting sites. In general, there is far less competition away from a group, and selection should favor any individual who (all things being equal) sets off on its own, leaving the members of its group behind to compete among themselves for limited resources. Another difficulty is that concentrations of individuals facilitate disease and parasite transmission. On the whole, social animals carry more parasites and speciesspecific diseases than do solitary animals. Parasites and diseases diminish the strength and limit the growth of animals, and among highly social creatures, epidemics can devastate whole populations. Distemper (a viral disease) has been known to wipe out entire colonies of seals, for instance. So the penalty of social life is potentiallyhuge.

　　3. What does paragraph 3 say about the relationship between natural selection and animals that live apart from other members of their species?

　　 Natural selection does not favor living apart because individuals are unable to obtain resources equal to those of group members.

　　 Natural selection does not favor living apart because of the intense competition for resources among individuals apart from a group.

　　 Natural selection favors living apart because individuals are unlikely to attract the attention of predators.

　　 Natural selection favors living apart because group living increases competition for limited resources of food and nesting sites.

　　4. The word "devastate " in the passage is closest in meaning to

　　 alter

　　 spread to

　　 destroy

　　 involve

　　5. In paragraph 3, why does the author mention distemper and its effect on seals?

　　 To explain why sociality is now relatively rare in seals 

　　To prove that parasites prevent animals from growing healthy and strong

　　 To show how easily social animals transmit potentially deadly diseases

　　 To provide an example of a species-specific disease that affects solitary animals

　　标题:社会性的动物

　　群居昆虫代表了无脊椎动物进化的高潮。一些物种生活在数以百万计的群体中，协调它们的建筑和觅食、繁殖和后代的照料。然而，只有少数种类的昆虫存在社会性，而且在脊椎动物中也很罕见:羚羊(大羚羊)和狮子是例外，而不是规则。几乎所有的鱼、两栖动物、爬行动物、鸟类和哺乳动物都是孤独的，除非是在求爱和交配的时候。鸟类和哺乳动物通常会养育它们的幼仔，但一年四季的家庭几乎是不为人知的，尽管它们的研究对象确实存在。昆虫也是如此。

　　我们知道，或者认为我们知道，社会群体是好的。狼是更好的捕食者，当它们成群猎食时，鸽子会从猎鹰中逃脱，更多时候是成群觅食。团体建筑工程——筑坝者建造水坝来阻挡水体，使它们相对安全，免受掠食者和他们为庇护所所建的小屋的保护，例如，可以提供高水平的保护和舒适。那么，为什么社会物种如此稀有呢?事实上，在社会生活中，生活中必然会出现超越生境需求的问题，因此只有当这些成本被相应的利益抵消时，才会有一群人活得更久。

　　最明显的代价就是竞争。一个物种的所有成员都有相同的栖息地;当它们生活在一起时，它们会尝试吃同样的食物，并占据相同的巢穴。总的来说，一个群体的竞争要少得多，而选择应该有利于任何一个人(所有的事物都是平等的)自己出发，让集团的成员在有限的资源中相互竞争。另一个困难是个体的浓度促进了疾病和寄生虫的传播。总的来说，社会动物比独居动物携带更多的寄生虫和物种特异性疾病。寄生虫和疾病削弱了动物的力量，限制了动物的生长，在高度社会化的生物中，流行病会毁灭整个种群。犬瘟热(一种病毒性疾病)已经被认为可以消灭所有的海豹群体，例如。因此，社会生活的惩罚可能是巨大的。

　　但在某些情况下，回报可能更大。其中有两个已经被提及:合作狩猎和防御团体。社会狩猎很可能会进化，因为猎物太大而不能单独行动。为了捕获角马，一些狮子跟随它们的猎物，把它们赶到埋伏的地方。在其他物种中，个体觅食或同时捕食并分享食物。例如，那些日子过得很糟糕的吸血蝙蝠，会被更成功的社区成员喂养，但他们在未来会得到回报。合作甚至可以分享有关食物位置的信息。一些殖民地的鸟类，如河岸燕子，利用一个成功的觅食者(食物猎人)的离开方向来定位猎物的浓度。信息传递可以是无意的，尽管有些物种利用特殊的集合调用或行为。

　　集体防御的合作，如我们在麝牛或大象的圈子里看到的，在脊椎动物中很少见，但在群居昆虫中很普遍。另一方面，用许多眼睛来观察危险的策略在鸟类和哺乳动物中很普遍。一群瞪羚(小羚羊)更有可能发现潜伏的狮子或隐藏的猎豹，而不是一个单独的个体，而且距离更远。事实上，一个群体进入了一种分时的安排，在这种安排中，每只羚羊都在不停地咬着一口草，一段时间的直立和警惕的咀嚼。一个更大的群体每分钟可以承受更多的叮咬，有更多的眼睛去扫描危险。然而，对于生活在森林中能见度有限的小羚羊来说，隐藏起来可能比聚集在喧闹的羊群中要好得多。

　　在几百万种昆虫中，只有几千种是社会性昆虫。这些稀有性一般局限于白蚁和膜翅目昆虫。所有白蚁都是社会性的:它们的饮食(纤维素)要求每一代都为下一代提供一种特殊的细菌或真菌以帮助消化。在众多的膜翅类动物中，有些是社会性的，包括所有的蚂蚁和一些蜜蜂和黄蜂，但许多都是独居的。

　　本条第一款

　　群居昆虫代表了无脊椎动物进化的高潮。一些物种生活在数以百万计的群体中，协调它们的建筑和觅食、繁殖和后代的照料。然而，只有少数种类的昆虫存在社会性，而且在脊椎动物中也很罕见:羚羊(大羚羊)和狮子是例外，而不是规则。几乎所有的鱼、两栖动物、爬行动物、鸟类和哺乳动物都是孤独的，除非是在求爱和交配的时候。鸟类和哺乳动物我们