It is obvious that humans are unlike all other animals. It is also obvious that we are a species of big mammal. That contradicti

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问题
    It is obvious that humans are unlike all other animals. It is also obvious that we are a species of big mammal. That contradiction is the most fascinating feature of the human species. It is familiar, but we still have difficulty grasping how it came to be and what it means. On the one hand, between ourselves and all other species lies a seemingly unbridgeable gulf that we acknowledge by defining a category called "animals". It implies that we consider centipedes, chimpanzees and clams to share decisive features with each other but not with us, and to lack features restricted to us. Among these characteristics unique to us are the abilities to talk, write, and build complex machines.
    Thus, for practical and legal purposes, humans are not animals. When Darwin intimated in 1859 that we had evolved from apes, it is no wonder that most people initially regarded his theory as absurd.
    On the other hand, we obviously are animals, with the usual animal body parts, molecules and genes. It is even clear what particular type of animal we an:. Externally, we are so similar to chimpanzees that eighteen-century anatomists who believed in divine creation could already recognize our affinities.
    Molecular genetic studies over the last half-a-dozen years have shown that we continue to share over ninety-eight percent of our genes with the other two chimps. The overall genetic distance between us and chimps is even smaller than the distance between such closely related bird species as red-eyed and white-eyed vireos, or willow warblers and chiffchaffs. So we still carry most of our old biological baggage with us. Since Darwin’s time, fossilized bones of hundreds of creatures variously intermediate between apes and modern humans have been discovered, making it impossible for a reasonable person to deny the overwhelming evidence.
    Yet the discoveries of many missing links have only made the problem more fascinating, without fully solving it. The two percent of our genes that differ from those of chimps must have been responsible for all of our seemingly unique properties. We underwent some small changes with big consequences rather quickly and recently in our evolutionary history.
    What were those few key ingredients that made us human? Since our unique properties appeared so recently and involved so few changes, those properties or at least their precursors must already be present in animals. What are those animal precursors of art and language, of genocide and drug abuse?
    Our unique qualities have been responsible for our present biological success as a species. No other large animal is native to all the continents, or breeds in all habitats from deserts and the Arctic to tropical rainforests. No large wild animal rivals us in numbers. But among our unique qualities are two that now jeopardize our existence: our propensities to kill each other and to destroy our environment. Of course, both propensities occur in other species: lions and many other animals kill their own kind, while elephants and others damage their environment. However, these propensities are much more threatening in us than in other animals because of our technological power and exploding numbers.
Questions 71 to 75
Complete the summary below with information from the passage, using three words or fewer for each blank.
We are still not clear about our【R1】______ history and what it means to us. Humans with unique attributes are obviously not animals, but judging from the appearance as well as【R2】______, we are a species of【R3】______. Humans possess some unique qualities which make us a species and surpass other animals. Two of our qualities threaten【R4】______, namely, our propensities to kill each other and to destroy our environment with【R5】______and great numbers.
【R4】

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答案our existence

解析 文章最后一段中间部分提到“But among our unique qualities are two that now jeopardize ourexistence.”,可见这里应该填our existence
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