Text b Sex, predators and the theory of evolution (Observing Darwin’s ideas in action)

What shapes a creature's life course and behavior? More than 130 years ago, Charles Darwin laid out his elegant and then shocking theory that it was natural selection, the survival of individuals most suited to the environment, that molded species over evolutionary time. But until very recently, Darwin's ideas remained unproved. Now, for the first time, studies in the wild are rigorously demonstrating the particulars of how evolution works.

Last month, David Reznick, an evolutionary ecologist at the University of California at Riverside, published the results of an 11-year experiment involving guppies living in the Aripo River of Trinidad. The experiment proved that predators are among the principal forces driving the evolution of species, just as predicted by a mathematical model that modern biologists had formulated to refine Darwin’s theme.

According to the model, animals that are preyed on as adults will evolve to produce as many babies as they can, as early in life as possible, "If your chances of dying young are good, then having babies yearly is important", says Reznick. However, the earlier a species reproduces, the sooner it bums out, so to speak, and the shorter its life span. Conversely, whose juveniles bear the brunt of predatory attacks, tend to have their young later in life, in effect choosing to bear hardier offspring over a longer adult life.

The experiment that Reznick devised, along with his colleagues, was delightfully uncomplicated. The researchers tested the mathematical model simply moving 200 guppies from the base of a 20-foot waterfall in the Aripo River, where predatory fish eat only adult guppies, to the top of the waterfall. There, the single predator is a killifish, a species that devours only young guppies.

After 60 generations, the experimental guppies had evolved in their new environment just as the model predicted. The fish now reach sexual maturity nine days later when they first give birth. What's more, they have fewer offspring in their first brood, apparently saving themselves for future breeding opportunities.

Reznick’s is only one of several recent studies verifying Darwin's grand theory in nature. In others, for instance, parasites are proving to be an even more potent agent of evolutionary change than predators. Marlene Zuk, a colleague of Reznick at Riverside, recently completed a study demonstrating that parasites affect how female jungle fowl, the wild ancestors of barnyard chickens, choose their mates. She found that nematode parasite, which lives in the gut, renders the eye and comb of the male fowl dull and consequently unattractive to females. The females prefer instead cocks bright of eye and comb, who will bestow their offspring with genes that will make them resistant to parasites.

Taken together, studies such as Reznick's and Zuk's, strike a resounding blow to all who would doubt veracity of evolution. It has taken more than a century, but Darwin's theory is finally being put to the test, as it is coming through with flying colors.

COMPREHENTION CHECK

Exercise 1.Read the text quickly and note its chief points by making a list of key words, topic sentences, names, places and numbers. Then re-read it for the specific information that will help you to answer the following questions.

1. Do we know in detail how evolution works?

2. Is "adaptation" the only factor contributing to evolution? Are there any other principal factors contributing to evolutionary changes in species?

3. Studies in the wild conducted by evolutionary ecologists are very helpful in understanding the particulars of evolutionary changes. How many experiments are described in the article and who conducted them?

4. What model is tested in the first experiment? Does it prove that there is a certain relationship between predatory attacks on a species and the period when it begins to reproduce?

5. What kind of fish was chosen for the first experiment?

6. How many generations of the experimental fish did it take to prove evolutionary changes?

7. Who conducted the second experiment which proved that sex relations among animals (the way they choose their mates) may affect the genetic composition of the offspring and may lead to evolutionary changes?

8. Which is the correct relationship established in the second experiment:

Rematode parasite → the specific genes → color of the eye and comb

Rematode parasite → color of the eye and comb → the specific genes

9. Do you think that Darwin's theory was successfully tested?

Exercise 2 .Highlight TEXT В taking the following steps:

Step 1: Read and translate TEXT В into Russian.

Step 2: Read carefully TEXT В making a list of key words and topic sentences.

Note 1: Key words and key terms are usually repeated; similarity of meaning or parts of meaning turns them into key words.

Note 2: Topic sentence summarizes the content of the whole paragraph.

Step 3: Look through the text quickly giving special attention to transitional words that help to connect ideas (but, though, despite, etc.).

Step 4: Look for such signals as the heading (Why is the text entitled the "Sex, predators and the theory of evolution"?), introductory and concluding paragraphs, names and numbers.

Step 5: Prepare for making an oral report in class on different aspects of the Darwin’s theory of evolution.

UNIT 5

PRE-TEXT TASK

Study carefully the meaning of the following phrases and word-combinations to avoid any difficulty in working through TEXT A.

1	environmental protection	защита окружающей среды
2	as well as	так же ... как
3	agricultural pollution control	контроль за загрязнением в сельском хозяйстве
4	genetic consequences of pollution	генетические последствия загрязнения окружающей среды
5	indiscriminate dumping of materials on land	беспорядочное вываливание отработанных веществ и материалов на землю
6	careless disposal of pesticides	небрежное использование пестицидов
7	fall-out	выпадение в виде осадков
8	...most of it being brought by winds	причем большая ее часть приносится ветрами
9	eventually	в конечном итоге, в конце концов
10	becomes upset	становится нарушенным
11	an ever-thinning ozone layer	постоянно истончающийся озоновый слой
12	ever-frozen	вечномерзлый
13	evergreen	вечнозеленый
14	ever-growing	постоянно растущий
15	to allow	делать возможным, приводить к ...
16	...speed and scale of change that human beings are inflicting on the world	скорость и масштабы тех отрицательных последствий /изменений/, которые люди наносят окружающей природе
17	rain forests	тропические леса
18	yet they only evolve to match -specific varieties of wheat	однако они развиваются только в том случае, если сочетаются с определенными сортами пшеницы
19	conservative forecasts	заниженные прогнозы