2. 外语
  3. Conventional wisdom has it that male birds are loyal and faithful because the business of feeding nestling is so demanding that

Conventional wisdom has it that male birds are loyal and faithful because the business of feeding nestling is so demanding that

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问题     Conventional wisdom has it that male birds are loyal and faithful because the business of feeding nestling is so demanding that it takes two to rear the clutch successfully. Cooperation is therefore the best way of ensuring reproductive success.
    By contrast, most mammals have a lengthy gestation (怀孕) follower by lactation (哺乳期), which leaves males on the sidelines. With little to contribute to the rearing process, they tend to opt for polygamy (一夫多妻) in one form or another.
    Male mammals are only monogamous (一夫一妻的) under a limited number of condition. One is when females are so widely dispersed that a male would find it difficult to defend more than one at a. time. In this case, he may do well to stick with one female to make sure that no other males mate with her when she does come into estrus (发情期). The dik-dik, a diminutive African antelope, is one species that seems to live by this role.
    However, many species are monogamous even when males could in principle defend several females. In these cases, it turns out that the male provides a service for the female. By investing in her and his young, the male gains more offspring in a lifetime than he does by pursuing the alternative strategy of polygamy.
    In South American marmoset and tamarin monkeys, this service amounts to full responsibility for everything to do with childcare, except lactation. As a result, females manage to produce twins twice a year—if they had to do all the work alone, it is unlikely that they could do better than a single infant once a year. So, males who become monogamous and share the workload can expect to obtain around four times as many offspring as males who abandon their mates in favor of serial polygamy. A polygamous male would have to locate and mate with at least four times as many females as a monogamous one, so it pays to be monogamous.
    As for humans, monogamy may have developed hand in hand with the evolution of large brains. Pair bonding could have ensured that women got enough food to raise-their big-brained, slow-growing and highly vulnerable offspring to adulthood. Our ancestors probably opted for some form of monogamy when they began eating meat and hunting.
The passage mainly discusses _______.
选项 A、division of labor between male and female mammals
B、how male are involved in the rearing process
C、how females choose their partners
D、factors affecting monogamy and polygamy
答案D
解析 主旨大意题。考查整篇文章的主题。A“雄性和雌性哺乳动物的劳动分工”和B“雄性如何参与到养育后代的过程中”只是文章在论述雌雄两性养育后代过程时提到的细节问题；C“雌性如何选择自己的伴侣”在文章中根本没有提到；D“影响一夫一妻和一天多妻的因素”是基于全篇的概括，文中第一段讲鸟类选择一夫一妻制的原因；第二段讲有些哺乳动物选择一夫多妻的原因；第三、四段讲了哺乳动物选择一夫一妻的原因；最后一段讲了人类在这方面的历史与发展，可见，全文都是围绕一夫一妻和一大多妻进行论述的，故选D。
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