可可英语在线听力
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The American Revolution was not a sudden and violent overturning of the political and socialframework, such as later occurred in France and Russia, when both were already independentnations. Significant changes were ushered in, but they were not breathtaking. What happenedwas accelerated evolution rather than outright revolution. During the conflict itself peoplewent on working and praying, marrying and playing. Most of them were not seriously disturbedby the actual fighting, and many of the more isolated communities scarcely knew that a warwas on.
America's War of Independence heralded the birth of three modern nations. One was Canada,which received its first large influx of English-speaking population from the thousands ofloyalists who fled there from the United States. Another was Australia, which became a penalcolony now that America was no longer available for prisoners and debtors. The thirdnewcomer-the United States-based itself squarely on republican principles.
Yet even the political overturn was not so revolutionary as one might suppose. In somestates, notably Connecticut and Rhode Island, the war largely ratified a colonial self-rule alreadyexisting. British officials, everywhere ousted, were replaced by a home-grown governing class,which promptly sought a local substitute for king and Parliament.
可可英语在线听力：Andrew CarnegieAndrew Carnegie, known as the King of Steel, built the steel industry in the United States, and, in the process, became one of the wealthiest men in America. His success resulted in part fromhis ability to sell the product and in part from his policy of expanding during periods ofeconomic decline, when most of his competitors were reducing their investments.
Carnegie believed that individuals should progress through hard work, but he also felt stronglythat the wealthy should use their fortunes for the benefit of society. He opposed charity,preferring instead to provide educational opportunities that would allow others to helpthemselves. "He who dies rich, dies disgraced," he often said.
Among his more noteworthy contributions to society are those that bear his name, includingthe Carnegie Institute of Pittsburgh, which has a library, a museum of fine arts, and a museumof national history. He also founded a school of technology that is now part of Carnegie-MellonUniversity. Other philanthropic gifts are the Carnegie Endowment for International Peace topromote understanding between nations, the Carnegie Institute of Washington to fundscientific research, and Carnegie Hall to provide a center for the arts.
Few Americans have been left untouched by Andrew Carnegie's generosity. His contributions ofmore than five million dollars established 2,500 libraries in small communities throughout thecountry and formed the nucleus of the public library system that we all enjoy today.
可可英语在线听力：烹饪进化论Science & Technology
The American Association for the Advancement of Science (AAAS)
What's Cooking?
Feb 19th 2009 | CHICAGO
From The Economist print edition
The evolutionary role of cookery
YOU are what you eat, or so the saying goes. But Richard Wrangham, of Harvard University,believes that this is true in a more profound sense than the one implied by the old proverb. Itis not just you who are what you eat, but the entire human species. And with Homo sapiens,what makes the species unique in Dr Wrangham’s opinion is that its food is so often cooked.
Cooking is a human universal. No society is without it. No one other than a few faddists triesto survive on raw food alone. And the consumption of a cooked meal in the evening, usually inthe company of family and friends, is normal in every known society. Moreover, without cooking,the human brain (which consumes 20-25% of the body’s energy) could not keep running. DrWrangham thus believes that cooking and humanity are coeval.
In fact, as he outlined to the American Association for the Advancement of Science (AAAS), inChicago, he thinks that cooking and other forms of preparing food are humanity’s “killer app”:the evolutionary change that underpins all of the other—and subsequent—changes that havemade people such unusual animals.
Humans became human, as it were, with the emergence 1.8m years ago of a species calledHomo erectus. This had a skeleton much like modern man’s—a big, brain-filled skull and anarrow pelvis and rib cage, which imply a small abdomen and thus a small gut. Hitherto, theexplanation for this shift from the smaller skulls and wider pelvises of man’s apelike ancestorshas been a shift from a vegetable-based diet to a meat-based one. Meat has more calories thanplant matter, the theory went. A smaller gut could therefore support a larger brain.
Dr Wrangham disagrees. When you do the sums, he argues, raw meat is still insufficient tobridge the gap. He points out that even modern “raw foodists”, members of a town-dwelling,back-to-nature social movement, struggle to maintain their weight—and they have access toanimals and plants that have been bred for the table. Pre-agricultural man confined to raw foodwould have starved.
Firelight
Start cooking, however, and things change radically. Cooking alters food in three importantways. It breaks starch molecules into more digestible fragments.
It “denatures” protein molecules, so that their amino-acid chains unfold and digestiveenzymes can attack them more easily. And heat physically softens food. That makes it easier todigest, so even though the stuff is no more calorific, the body uses fewer calories dealing withit.
In support of his thesis, Dr Wrangham, who is an anthropologist, has ransacked other fieldsand come up with an impressive array of material. Cooking increases the share of fooddigested in the stomach and small intestine, where it can be absorbed, from 50% to 95%according to work done on people fitted for medical reasons with collection bags at the ends oftheir small intestines. Previous studies had suggested raw food was digested equally well ascooked food because they looked at faeces as being the end product. These, however, havebeen exposed to the digestive mercies of bacteria in the large intestine, and any residualgoodies have been removed from them that way.
Another telling experiment, conducted on rats, did not rely on cooking. Rather theexperimenters ground up food pellets and then recompacted them to make them softer. Ratsfed on the softer pellets weighed 30% more after 26 weeks than those fed the same weight ofstandard pellets. The difference was because of the lower cost of digestion. Indeed, DrWrangham suspects the main cause of the modern epidemic of obesity is not overeating(which the evidence suggests—in America, at least—is a myth) but the rise of processedfoods. These are softer, because that is what people prefer. Indeed, the nerves from the tastebuds meet in a part of the brain called the amygdala with nerves that convey information onthe softness of food. It is only after these two qualities have been compared that the brainassesses how pleasant a mouthful actually is.
The archaeological evidence for ancient cookery is equivocal. Digs show that both modernhumans and Neanderthals controlled fire in a way that almost certainly means they could cook,and did so at least 200,000 years ago. Since the last common ancestor of the two specieslived more than 400,000 years ago (see following story) fire-control is probably at least as oldas that, for they lived in different parts of the world, and so could not have copied each other.
Older alleged sites of human fires are more susceptible to other interpretations, but they doexist, including ones that go back to the beginning of Homo erectus. And traces of fire areeasily wiped out, so the lack of direct evidence for them is no surprise. Instead, Dr Wranghamis relying on a compelling chain of logic. And in doing so he may have cast light not only onwhat made humanity, but on one of the threats it faces today.
