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  3. SOCIALITY IN ANIMALS (1) Social insects represent the high point of invertebrate evolution. Some species live in communities

SOCIALITY IN ANIMALS (1) Social insects represent the high point of invertebrate evolution. Some species live in communities

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问题                                             SOCIALITY IN ANIMALS
    (1) Social insects represent the high point of invertebrate evolution. Some species live 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.
    (2) We know, or think we know, that social groups are good. [A] Wolves are better predators when they hunt in packs, and pigeons escape from falcons far more often when feeding in flocks. [B] Group building projects—the dams beavers build to block a body of water provide them with relative safety from predators and the lodges they build for shelter, for instance—can provide a high level of protection and comfort. [C] Why, then, are social species so very rare? [D] 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.
    (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 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.
    (4) 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.
    (5) 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 antelopes 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 noisy herds.
    (6) 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 feeds 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.
Look at the four squares [ ■ ] that indicate where the following sentence can be added to the passage. The engineering of structures of such size and complexity is unknown among solitary animals.
Where would the sentence best fit?
选项
答案C
解析 本题属于插入句子题，被插入句子有structures of such size and complexity (如此规模和复杂程度的结构)这种需要往前回溯的提示性表达(such)。第2段的四个方框所在处只有C处前提到了dams (水坝)、lodges(小屋)这些建筑结构，而原文中的Group building projects对应被插入句子的of such size and complexity。由此可判断，该句子放在C处才能使前后逻辑一致，故选。A、B、D 三处的前一句均无与“如此规模和复杂程度的结构”相关的信息，所以若把插入句放入这三处，则前后逻辑均不符。
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