Natural Selection First coined by Darwin, the term natural selection refers to the process at the core of evolutionary theory. Simply put, Darwin believed that every living organism had to struggle to survive and reproduce. By random chance, some individuals in a species would have characteristics that made them better adapted to this struggle than their contemporaries. Such individuals would be more likely to reproduce and pass their characteristics on to their offspring. Over many generations, a series of small differences in characteristics would accumulate, until eventually the creatures that were produced would be so different from their original ancestors that they would constitute a new species. ■(A) Although Darwin did not know how variations between individual members of the same species were able to arise in the first place or how such traits could then be passed on from species to species, we now know that this process occurs through genes. ■(B) Genes determine what characteristics an organism will possess, from its size to its skin color to its gender. ■(C) Sometimes these genes become damaged or altered--a process known as mutation. ■(D) Most mutations are either too small to have any effect, or have detrimental effects on the organism. A few, however, can be beneficial to helping an organism survive. The organisms with these beneficial mutations are the ones that .survive and reproduce, passing their particular genetic mutation on to future generations. Originally, Darwin thought that two particular types of traits were naturally selected for evolution. The first type included any and all traits that helped an organism survive, either by giving it easier access to food, better protection from predators, or superior adaptability to shifting environmental conditions. Several examples of the natural selection of such traits have been observed since Darwin first proposed his theory. The most often cited example is the coloration of moths near industrial centers. Some of them have white wings and the others have black wings. Under normal conditions, the lighter-colored moths predominate since white moths are less visible against the light-colored bark of the trees in the forests where they live, which means they can more easily avoid predators. Near industrial centers, however, darker-colored moths predominate, as the pollution from the factory has darkened the bark of the nearby trees. Moths landing on these trees are much more difficult to see if they have black wings. This trait has now become most common in moth populations living in areas where pollutants have changed the color of the tree bark. The second type of naturally selected traits envisioned by Darwin involved those characteristics of an organism that made it easier for that organism to find a mate. This form of natural selection, often called sexual selection, was thought to explain the existence of highly developed traits in certain animals that seemed to play no particular role in their survival, and that in some cases seemed to make it even harder for them to survive. A prime example of such a trait is the peacock’s elaborate, colorful tail feathers. A long, unwieldy tail that can expand into a display of bright colors that draws the attention of any predator in the vicinity seems less likely than that of other kinds of birds to help the bird survive. However, researchers discovered that peahens invariably chose to mate with those peacocks whose tail feathers produced the most artistic displays. Thus, although the peacock’s tail feathers have no adaptive function in terms of coping with survival pressure, the gene that controls feather color is the one that is most likely to be passed on because of its role in the mating process. Many scientists now believe that a third type of naturally selected characteristics exists, namely those that may be harmful to an individual organism but beneficial to that organism’s species. This helps to explain the persistence of certain traits that were viewed under traditional evolutionary theory as not assisting in adaptation. For instance, in many animal species, including humans, a small subset of the population is homosexual. Under the old view of evolution, this could not be accounted for since homosexual individuals do not normally reproduce, meaning the gene that codes for it should have long been phased out of the gene pool. However, recent studies among wild sheep populations have found that the prevalence of homosexuality in the sheep population increases in times of severe food shortages, causing the sheep to form stronger bonds with sheep of the same sex than they otherwise would. As a result, instead of fighting over a particular food source, these sheep share the food they find with each other, increasing the species’ chance of surviving hard times. Though still controversial, the idea that traits may be naturally selected because of their benefits to the species instead of their benefits to the individual is rapidly gaining acceptance in the scientific community because of the wide array of characteristics that it can explain, including the human tendency towards altruism, What do peahens look for in peacocks
A. Large wing feathers.
B. Loud mating calls.
C. Artistic tail displays.
D. Colorful breast plumag
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Passage Four The comprehension passages on this course are designed to help you increase your speed. A higher reading rate, with no loss of comprehension, will help you in other subjects as well as English, and the general principles apply to any language. Naturally, you will read every book at the same speed. You would expect to read a newspaper, fox example, much more rapidly than a physics or economics textbook but you can raise your average reading speed over the whole range of materials you wish to cover so that the percentage gain will be the same whatever kind of reading you are concerned with. The reading passages which follow are all of an average level of difficulty for your stage of instruction. If you get to the point where you can read books of average difficulty at between 40 and 50 w.p.m. with 70% or more comprehension, you will be doing quite well, though of course any further improvement of speed with comprehension will be a good thing. When you practise reading with passages shorter than book length, do not try to take in each word separately, one after the other. It is much more difficult to grasp the broad theme of the passage this way, and you will also get stuck on individual words which may not be absolutely essential to a general understanding of the passage. It is a good idea to skim through the passage very quickly first (say 500 words in a minute or so) to get the general idea of each paragraph. Titles, paragraph headings and emphasized words (underlined or in italics) can be a great help in getting this skeleton outline of the passage. Which of the following statements is TRUE according to the passage
A. You are expected to read various kinds of materials at the same rate.
B. A great deal of specialized knowledge is required to read books of general interest.
C. Titles, introduction and paragraph heading are of great help for grasping the overview of the text.
D. It is less likely that you can raise your average reading rate over the whole range of materials you wish to cover within a short time.
Passage Four The comprehension passages on this course are designed to help you increase your speed. A higher reading rate, with no loss of comprehension, will help you in other subjects as well as English, and the general principles apply to any language. Naturally, you will read every book at the same speed. You would expect to read a newspaper, fox example, much more rapidly than a physics or economics textbook but you can raise your average reading speed over the whole range of materials you wish to cover so that the percentage gain will be the same whatever kind of reading you are concerned with. The reading passages which follow are all of an average level of difficulty for your stage of instruction. If you get to the point where you can read books of average difficulty at between 40 and 50 w.p.m. with 70% or more comprehension, you will be doing quite well, though of course any further improvement of speed with comprehension will be a good thing. When you practise reading with passages shorter than book length, do not try to take in each word separately, one after the other. It is much more difficult to grasp the broad theme of the passage this way, and you will also get stuck on individual words which may not be absolutely essential to a general understanding of the passage. It is a good idea to skim through the passage very quickly first (say 500 words in a minute or so) to get the general idea of each paragraph. Titles, paragraph headings and emphasized words (underlined or in italics) can be a great help in getting this skeleton outline of the passage. Provided there is no loss understanding, a higher reading speed will help in ______.
A. English
B. physics
C. other subjects as well as English
D. economics
Passage Two Do you find getting up in the morning so difficult that it’s painful This might be called laziness, but Dr. Kleitman has a new explanation. He has proved that everyone has a daily energy cycle. During the hours when you labor through your work may say that you’re "hot". That’s true. The time of day when you feel most energetic is when your cycle of body temperature is at its peak. For some people the peak comes during the forenoon. For others it comes in the afternoon or evening. No one has discovered why this is so, but it leads to such familiar monologues (独白) as: "Get up, John! You’ll be late for work again!" The possible explanation to the trouble is that John is at his temperature-and-energy peak in the evening. Much family quarreling ends when husbands and wives realize what these energy cycles mean, and which cycle each member of the family has. You can’t change your energy cycle, but you can learn to make your life fit it better. Habit can help, Dr. Kleitman believes. Maybe you’re sleepy in the evening but feel you must stay up late anyway. Counteract (阻碍) your cycle to some extent by habitually staying up later than you want to. If your energy is low in the morning but you have an important job to do early in the day, rise before your usual hour. This won’t change your cycle, but you’ll get up steam and work better at your low point. Get off to a slow start which saves your energy. Get up with a leisurely yawn (哈欠) and stretch. Sit on the edge of the bed a minute before putting your feet on the floor. Avoid the troublesome search for clean clothes by laying them out the night before. Whenever possible, do routine work in the afternoon and save tasks requiring more energy or concentration for your sharper hours. You are advised to rise with a yawn and stretch because it will ______.
A. help to keep your energy for the day’s work
B. keep your energy cycle under control all day
C. help you to control your temper early in the day
D. enable you to concentrate on your routine work
患者,男,35岁,因在高热环境下持续工作12小时而出现头痛、头晕、乏力、多汗等症状,不久体温迅速升高到41℃,并出现颜面潮红、昏迷、休克此时最佳的降温措施应为
A. 冰盐水灌肠
B. 冰帽
C. 静脉滴注葡萄糖盐水
D. 冬眠合剂
E. 物理降温十药物降温