Арсланова_Г_А_и_др_Essential_English_for_Biology_Students (1). Kazan federal university
 Скачать 7.01 Mb.
|
UNIT VI. EVOLUTIONText 6.1. Theories Of Evolution■  Essential targets:By the end of this text you should be able to: ● explain the biological meaning of evolution; ● distinguish between neo-Darvinism and Darvinism. Pre-reading ■ Working in pairs, try to answer the following questions before you read the text. When you have finished, check your answers by reading the text. What is evolution? How does it happen? What is a species? What is natural selection? What theory did Darwin develop? ■ Read the given text and make your essential assignments: One of the most fundamental questions in biology is: where do all living things come from? According to most biologists, the millions of species living on Earth today (including humans) are descended from other species that inhabited the world in the past. This change has come about by a process called evolution. Evolution happens when the genetic composition (allele frequency) of a population changes over successive generations. When the changes are sufficiently great, a new species may be formed. (A species is a group of closely related organisms potentially capable of interbreeding to produce fertile offspring.) 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 19th 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. B  etween 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: How does the evolution usually take place? What led Charles Darwin to develop his theory of evolution? What did Darwin mean by “natural selection”? What are three main observations of Darwin’s theory? What does “struggle for existence” mean? What book has been called the most important biology book ever written? Do the majority of biologists accept Darwin’s theory? What is called neo-Darwinism? IX. Match the sentence halves. Make complete sentences:
X. Read and translate the short text without any dictionary: Fact of life: Highly sensitive dating techniques tell us that the Earth is between 4.5 and 5.0 thousand million years old. It is generally agreed by scientists that the Earth was originally devoid of life, and that the first living organisms arose by biochemical evolution from complex organic chemicals formed in the atmosphere and seas of early Earth. These first forms of life gave rise to countless millions of species. Most have become extinct, but some have evolved into organisms found today. According to the latest estimates, 20-30 million species share our planet. XI. Food for thought: In 1809 Jean-Baptiste de Lamark suggested that the driving force behind evolution was the need for organisms to adapt to changing environmental conditions. His theory became known as the theory of evolution by the inheritance of acquired characteristics. He believed that adaptations developed by an organism during its lifetime could be passed on to its offspring. According to Lamark, modern giraffes might have evolved from a short-necked ancestors in the following way. Giraffes feed on leaves ripped off the branches of trees. When leaves on the lower branches were removed, or when the trees became taller, the ancestral giraffe needed to stretch to reach leaves on higher branches. By continually stretching, their necks lengthened and the ability to grow a slightly longer neck was inherited by the next generation which carried on stretching, and so on. We know that this explanation of the evolution of the giraffe’s neck is untrue because activities such as stretching to feed do not affect the gametes. Therefore, this type of characteristic acquired during the life of an organism is not inherited by its offspring. Expressed in modern terms, Lamarckism would mean that changes in phenotype could determine the genotype of future generations. This does not agree with modern genetics, and there are no generally accepted examples of acquired characteristics being inherited. Suggest a neo-Darwinian explanation for the evolution of the modern long-necked giraffe from a short-necked ancestor. |