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  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.
We can infer that the chance for female marmoset and tamarin monkeys to have twin births depends on ______.
选项 A、the number of male they have access to
B、the workload they have in bringing up the young
C、the time when they come into estrus
D、the size of the males’ bodies
答案B
解析 推理判断题。根据文中第五段可以判断出选项B“她们在养育后代中的工作量”是与文章中第五段所作的论述完全符合的。A“她们所能接触到的雄性数量”与文章的论述在逻辑上不符：C“她们进入发情期的时间”和D“雄性动物的体型大小”在第五段中根本没有提到。
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