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Theory of Evolution

Evolution as defined in biology, the continual process by which one form of life changes, or evolves, into another form. Some religious groups deny that evolution exists, but most scientists accept it as fact. The theory of evolution suggests that all plants and animals descended from one or several kinds of simple organisms. It also explains why there are so many different kinds of plants and animals. The inherited characteristics of nearly all living things change from generation to generation. In most cases, this change is so gradual that it is noticeable only after many years.

Eventually the accumulated changes may become so great that the descendant bears little likeness to its remote ancestor and may belong to different species. II. Discussion A. How evolution takes place? Natural selection. There are more plants and animals produced than can possibly survive, because there is not enough space and food to support them. The result is competition between living organisms in the struggle for survival. The individuals in each group are not all exactly alike. They have varying characteristics, and these variations may either help or hinder them in their struggle to live.

Organisms become extinct and die out, if they do not have enough of the kind of characteristic that enable them to get sufficient food and other necessities to withstand the climate, or to compete successfully with other forms of life. Mutation. To explain how plants and animals develop variations, biologists turn to genetics, the science of heredity. Genetics shows that characteristics are passed from parents to offspring by means of genes. When a gene is altered in anyway, the offspring acquires a new characteristic not possessed by either parent. This change in the genes is called mutation.

Sexual Recombination. The combining of genes from two parents is called sexual recombination and controls the rate at which variations occur. It permits enough variation to allow progressive evolution but not so much variation that the changes would be chaotic. The survival value of recombination is indicated by the fact that the large majority of plants and animals produce sexually. Isolation. New species of plants and animals can appear only when a genetically distinctive population is prevented from exchanging genes with closely related populations.

Geographic isolation, or the separation of related groups by some kind of physical barrier such as mountain or desert, is the most usual type. Genetic isolation is the inability of the members of two related groups to bear fertile offspring when mated. B. History of the Theory of Evolution Many ancient myths were attempts to explain how the various plants and animals were created. Thales suggested that all life came from water. Aristotle believed that living things could arise out of non-living matter, and that more complex forms of life probably arose from simpler forms.

With spread of Christianity, men throughout the Western World accepted the story of Creation as told in Genesis, the first book of the Bible. For hundreds of years no further scientific though was devoted to the origin of life. By the 18th century scientists had again begun to investigate the development of living things. George Louis Buffon thought that environment acted directly to change the structure of plants and animals. Erasmus Darwin and Jean Baptiste Lamarck each advanced the now discredited theory that organisms inherit adaptations acquired during the lifetime of their parents.

The basis for the modern theory of evolution was formulated independently by Charles Darwin, grandson of Erasmus Darwin, and by Alfred Russel Wallace. They introduced their ideas about natural selection in joint papers read to a London learned society in 1858. Darwin’s Origin of Species in 18599, made the theory very famous. The Darwin- Wallace theory was incomplete, however, because neither man knew much about genetics. Gregor Mendel discovered the laws of heredity in the 1860’s, but his findings were neglected until 1900.

In 1937 the theories of natural selection and genetic variability were fused by Theodozius Dobhanzsky, a Russian born American biologist, in Genetics and Origin of Species. Dobhanzsky’s theory, called the Synthetic Theory, states that evolution is a two- step process. In the first step, genetic variations occur through mutations or by a chance combination of inherited genes. In the second step, desirable variations—those that produce traits that help the organism survive—are passed on to the next generation and become permanently established in the species.

When the theory of evolution first came to public attention in 1859 it was met with a storm protest and ridicule. Some people, misinterpreting the theory, thought it claimed that man was descended from apes. One religious objection to evolution was that it conflicted with the story of Creation as told in Genesis. In the United States some states passed laws making it illegal to teach evolution in public schools. Most religious denominations now accept the theory, but in varying degrees. Some see no conflict between evolution and theology.

Others accept the theory only as an unproved hypothesis still others accept only those parts that do not apply to man. A theory called Scientific Creationism states that scientific evidence points not to man’s evolution from lower species but to his creation by some external power or intelligence.

References: 1. Benton, Michael. The Story of Life on Earth. Watts, 1986. 2. Stein, Sara. The Evolution Book: the Story of 4000 Million Years of Life on Earth. Workman, 1986. 3. Whitcomb, J. C. , and H. M. Morris. The Genesis Flood: the Biblical Record and its Scientific Implications. Presbyterian & Reformed, 1982.

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