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  3. "Why are humans so smart?" is a question that fascinates scientists. Tadeusz Kawecki, an evolutionary biologist at the Universit

"Why are humans so smart?" is a question that fascinates scientists. Tadeusz Kawecki, an evolutionary biologist at the Universit

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问题     "Why are humans so smart?" is a question that fascinates scientists. Tadeusz Kawecki, an evolutionary biologist at the University of Fribourg, likes to turn around the question. "If it’s so great to be smart," Dr. Kawecki asks, "why have most animals remained dumb?"
    Dr. Kawecki and like-minded scientists are trying to figure out why animals learn and why some have evolved to be better at learning than others. One reason for the difference, their research finds, is that being smart can be bad for an animal’s health. Learning is remarkably widespread in the animal kingdom. The worms are not born with an innate aversion to the dangerous bacteria. They need time to learn to tell the difference and avoid becoming sick.
    Dr. Dukas hypothesizes that any animal with a nervous system can learn. Even in cases where scientists have failed to document learning in a species, he thinks they should not be too quick to rule it out. "Is it because I’m not a good teacher or because the animal doesn’t learn?" Dr. Dukas asked.
    Although learning may be widespread among animals, Dr. Dukas wonders why they bothered to evolve it in the first place. "You cannot just say that learning is an adaptation to a changing environment," he said. It is possible to adapt to a changing environment without using a nervous system to learn. Bacteria can alter behavior to help their survival. If a microbe senses a toxin, it can swim away. If it senses a new food, it can switch genes on and off to alter its metabolism.
    Learning also turns out to have dangerous side effects that make its evolution even more puzzling. Dr. Kawecki and his colleagues have produced striking evidence for these side effects by studying flies as they evolve into better learners in the lab.
    Dr. Kawecki suspects that each species evolves until it reaches an equilibrium between the costs and benefits of learning. His experiments demonstrate that flies have the genetic potential to become significantly smarter in the wild. But only under his lab conditions does evolution actually move in that direction. In nature, any improvement in learning would cost too much.
    Dr. Kawecki also says it is worth investigating whether humans also pay hidden costs for extreme learning. "We could speculate that some diseases are a byproduct of intelligence," he said. The benefits of learning must have been enormous for evolution to have overcome those costs, Dr. Kawecki argues.
The underlined word in Paragraph 6 refers to______.
选项 A、agreement
B、conclusion
C、balance
D、equality
答案C
解析 属词义推断题。文章第五段中讲到动物的学习行为具有危险的副作用，第六段果蝇的例子也指出在自然界中学习的代价太大了。所以单词所在句可以这样理解：动物不断进化，学习各种技能，但是也要付出一定的代价，等到学习的好处与代价达到均衡的态势时进化就停止了，因为如果继续进化很可能带来代价大于好处的后果。因此可知，所考查单词的意思是“均衡，平衡”，故选项C正确。选项A、B、D均不符合文意，故错误。
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