雅思阅读分析：Chili peppers

Origins

Chili peppers, the fruit of the capsicum plant, are believed to have originated in what is now Bolivia in South America, home to dozens of wild species that are probably the ancestors of each and every chili variety today, from mild green peppers to fiery hot naga jolokia peppers. Every chili pepper contains a heat-generating ingredient known as capsaicin, which has long been known to affect human taste buds, nerve cells and nasal membranes. People have been spicing their foods with chilies for at least 8,000 years. Archaeobotanist Linda Perry, at the Smithsonian Institution, Washington DC in the US, has found traces of chilies on ancient stones used to grind grains, and in vessels used in food preparation from the Bahamas to southern Peru.

Based on her examination of ancient pieces of pottery, Ms Perry concludes that people in the Americas began cultivating chilies more than 6,000 years ago. "Chilies were domesticated early and spread very quickly, just because people liked them," she says. The chilies, it would seem, made otherwise quite bland food more enjoyable to eat. Other researchers, such as Jennifer Billing and Paul Sherman of Cornell University in the US, argue that people learned early on that chilies could reduce food spoilage. And some scholars point to medical uses: ancient Mayan Indians in Central America incorporated chilies into medicinal preparations for treating wounds, stomach problems and earaches.

Spreading chili peppers around the world

Whatever the benefits, chilies spread around the world at astonishing speed, thanks in part to Christopher Columbus, who is credited with being the first European to reach America in 1492, and claiming the new land for Spain. When Columbus took chilies back to Spain, they were initially not popular, but soon became widely accepted throughout Europe. The Portuguese first encountered chilies in Brazil and carried them, along with tobacco and cotton, to Africa. By 1550, chilies were being cultivated all over the world, including in India, Japan and China.

The heat of chili peppers

When people call chilies hot, they are not just speaking metaphorically. Capsaicin stimulates the neural sensors in the tongue and skin that also detect rising temperatures. As far as these neurons and the brain are concerned, when someone eats a hot chili, the effect is the same as exposure to fire. With enough heat, adrenaline flows and the heart pumps faster. This reaction, according to some physiologists, is part of what makes peppers so stimulating and enjoyable to eat.

The scale that scientists use to describe a chili's heat was developed in 1912 by Wilbur Scoville, a chemist from Detroit in the US. He diluted a chili extract in sugar water until the heat was no longer detectable to a panel of trained tasters; that threshold is the basis of the Scoville rating. A sweet bell pepper, for instance, measures zero on the Scoville Heat Unit (SHU) scale, while a typical hot jalapeno chili pepper from Mexico falls between 2,500 and 8,000 SHUs. Last year, the naga jolokia chili, grown in India, was rated at one million SHUs.

The role of capsaicin

But why would chilies have evolved to produce the varying degrees of heat of capsaicin? Chili seeds, like other fruit, lure birds and other animals to eat them and disperse their seeds. But chilies also attract rodents, large animals like rats and mice, that crush seeds and make germination impossible. In order to deter animals from eating their seeds, many plants produce toxic or foul-tasting chemicals, but these are usually found just in the plant's leaves and roots as well as its fruit. In chilies, however, capsaicin is found just in the fruit, and becomes much stronger with ripening. Joshua Tewksbury, an ecologist at the University of Washington in the US, suspected that at least one role that capsaicin performs is to protect the chili seeds from rodents.

To test this theory, Tewksbury grew plants that produced hot, spicy chilies as well as plants that yielded mild chilies (though both were from the same species). When he offered the fruits of the mild plants to laboratory rats and mice, they ate them without hesitation. The rodents avoided the hot chilies, however, even though the taste of the capsaicin has been likened to that of a gold rush). However, the kauri that was used here was from the forest floor, and King's misconceptions sum up the prejudice that surrounded the project.

In another experiment, Tewksbury offered birds the same selection of mild and hot chilies. Unlike the rodents, the birds ate the hot chilies as readily as the mild ones. The reason, Tewksbury believes, is that birds do not have the same neural receptors as mammals. For a bird, eating a chili pepper is no more painful than eating a sweet pepper.

Tewksbury also found that when birds eat chili seeds, the seeds pass through their digestive systems unharmed and can germinate later. In fact, the seeds that have passed through a bird's gut may even be more likely to germinate than those that have not. Tewksbury thinks that capsaicin may actually serve another purpose: by slowing down digestion in birds, it may help the seeds to stay in the bird's gut longer, thus increasing the distance the seeds are dispersed. This would be especially beneficial for a plant that is trying to colonize new areas.

But wait, there's more. Capsaicin may also protect the chili plant from disease. In a study published in the journal *Proceedings of the National Academy of Sciences*, Tewksbury and his colleagues found that capsaicin inhibits the growth of a certain fungus that can infect chili seeds. The heat of the chili, it seems, is not just a defense against hungry rodents but also a way to keep the seeds healthy.

So, the next time you bite into a spicy chili pepper and feel the burn, remember that you're experiencing the result of millions of years of evolution. As Tewksbury puts it, "Capsaicin demonstrates the incredible elegance of evolution."

Questions 1-6

Do the following statements agree with the information given in Reading Passage 1?

In boxes 1-6 on your answer sheet, write

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

Questions 7-13

Complete the notes below.

Choose ONE WORD ONLY from the passage for each answer.

Write your answers in boxes 7-13 on your answer sheet.

判断题（1-6）

填空题（7-13）