The mechanism of evolution.

Evolution is not a modern concept. Since ancient times, a number of philosophers and naturalists (including Confucius and Aristotle in Greece) have suggested that complex species evolve from simpler pre-existing ones by a process of continuous and gradual change. However, it was not until the 19^th century that scientists came up with plausible mechanisms for evolution. The mechanism that is widely accepted among biologists today is called neo-Darwinism. It is modern theory based on the work of the nineteenth- century naturalist Charles Darwin.

Between 1831 and 1836, Darwin was the naturalist on board HMS Beagle, a research vessel engaged in mapping different parts of the world. After spending over three years surveying the coast of South America, the Beagle landed on the Galapagos Islands in the Pacific Ocean. Darwin compared the organisms on these islands with those on the South American mainland, and this led him to develop his theory of evolution. He came to the conclusion that, over successive generation, a new species comes into being by slow and gradual changes from a pre-existing one. He believed that these changes are brought about by a process which he called natural selection.

Darwin’s theory was based on three main observations:

1. Within a population are organisms with varying characteristics, and these variations are inherited (at least in part) by their offspring.

2. Organisms produce more offspring than are required to replace their parents.

3. On average, population numbers remain relatively constant and no population gets bigger indefinitely.

From these observations, Darwin came to the conclusion that within a population many individuals do not survive, or fail to reproduce. There is a “struggle for existence”. For example, members of the same population compete to obtain limited resources, and there is a struggle to avoid predation and disease, or to tolerate changes in environmental conditions such as temperature. In this struggle for existence those individuals that are best adapted to their environment will have a selective advantage: they will be more likely to survive and produce offspring than less well-adapted organisms.

The origin of species

For more than 20 years, Darwin collected evidence to support his theory and refined his ideas. He delayed publishing his ideas until 1858, when Alfred Russel Wallace sent him a letter describing a theory of evolution identical to Darwin’s own. Wallace was a British naturalist who had worked in the Malay Archipelago for eight years. He concluded from his research that some organisms live while others die because of differences in their characteristics, such as their ability to resist disease or escape predation. Darwin and Wallace published a paper jointly describing their theory of evolution by natural selection. However, Darwin’s name has become more strongly linked with the theory because of a book he published on 24 November 1859. The book, entitled “The Origin of Species by Means of Natural Selection or the Preservations of Favoured Races in the Struggle for Life”, has been called the most important biology book ever written. It not only gives a full description of the theory of evolution by natural selection, but also contains a huge mass of evidence to support the theory.

The reaction to Darwin.

Many people found it difficult to accept Darwin’s ideas, especially the idea that modern humans and apes are probably descended from a common ancestor. However, his theory is supported by so much evidence that the majority of biologists accept it. Evolution by natural selection has become a central theme which underpins much of modern biology. The modern theory of evolution is called neo-Darwinism because it incorporates new scientific evidence, particularly from genetics and molecular biology. For example, we know that the variations that are so important in natural selection come about by random and spontaneous changes in genes, particularly from mutations in reproductive cells. Despite modifications to Darwin’s theory in neo-Darwinism, natural selection is still the driving force behind evolution, or the theory of evolution by the natural selection of inherited characteristics.

■ Glossary of essential terms for you to know

■ Your Essential Assignments

I. Quick check:

1. Give the biological meaning of evolution.

2. How does neo-Darwinism differ from Darwin’s original theory of evolution?

II. Fill in the missing words:

III. Use monolingual English dictionary and write down what could the words given below mean:

change, naturalist, complex, to escape, to collect, humans.

IV. Match these words with their definitions:

V. Find English equivalents to the following word combinations:

VI. Give Russian equivalents to the following English terms:

VII. Find synonyms among the pool of words:

VIII. Answer the following questions. Use all information given before:

1. How does the evolution usually take place?

2. What led Charles Darwin to develop his theory of evolution?

3. What did Darwin mean by “natural selection”?

4. What are three main observations of Darwin’s theory?

5. What does “struggle for existence” mean?

6. What book has been called the most important biology book ever written?

7. Do the majority of biologists accept Darwin’s theory?

8. What is called neo-Darwinism?

IX. Match the sentence halves. Make complete sentences:

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