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Analyzing Topic Sentences

An important skill for reading is finding the main idea. Sometimes the main idea of a paragraph is stated directly. The sentence that states it is called the topic sentence.

Find the topic sentence in each paragraph.

Talking it over

1 What do you understand under "relationships and interdependencies" that developed between the living organisms?

2 Is technology the main problem for environment contamination? Explain your choice.

3 Why are people eager to fulfill their short-term needs and don’t think about long-term welfare?

4 What do people do to fill their inner gap? How can it affect the environment?

Read and translate the text orally:

Evolution

People have always been curious about the creator of all ani­mals and plants. There have been many divine theories about how people came into being. However, research findings have proved that all animals including human beings have evolved from primitive ancestors. In 1859 Charles Darwin put forward his theory of evolution, which claimed that all animals changed and developed during a con­tinuous process. This process is brought about by the species gradu­ally adapting to the demands of its environment, through a gradual genetic change.

To understand this complicated process some theoretical back­ground is necessary.

Inside each of our body's cells, there is a complex substance known as DNA. It looks like a very twisted ladder and its full name is deoxyribonucleic acid. Sections of DNA are known genes. They give instructions about when different types of cells should develop, and whereabouts in the body they should be. DNA bears the genetic code which is a tremendously complicated set of instructions to the cells in the body, so that they will know how to develop. As a result of these complex instructions, we develop specialized liver cells, heart cells, hair cells, skin cells, and all other different types of cells, which make up a body.

Larger strands of DNA are known as chromosomes. They are arranged in pairs. However, an ovum, a female cell capable of developing into a baby as well as a male cell that should fertil­ize it have only half of the chromosomes. In this way, when organ­isms reproduce themselves sexually, — by combining sperm from one parent with ova from another, — the new individual possesses charac­teristics of both parents.

The new combination of characteristics may be particularly beneficial.

The child may inherit the very best features of its parents and be healthier, stronger and fitter. Sometimes, there are slight mistakes made in the copying. When the special reproductive cells are made, and these can result in the new individual being different in someway. These mistakes are known as genetic mutations and sometimes are very beneficial. When these beneficial changes, evolution happens.

Every organism is in competition with other members of its spe­cies. So anything, which helps this plant or animal to get an edge over the competition, will be useful. The individuals with beneficial charac­teristics are more likely to survive if some natural change happens. This is known as natural selection, which is all about the survival of the fittest — and the fittest is the one, which is best adapted to its envi­ronment. It should be clear now that it is a mistake to think of evolu­tion as a straight-line development leading up to the human being. This is only one of many different branches of evolution.

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