ORGANIZATION PRACTICE:

Mapping Instructions:Read the following passage on principles of classification, and then do a concept map -- from memory -- of everything you can remember of the passage. Classification consists of placing together in categories those things that resemble each other. While this sounds simple, in actual practice it may be quite difficult. First of all, we have to decide what kind of similarities are the most important for our purpose. One of the earliest classification schemes placed in one category all those organisms which lived in the same habitat. Thus fish, whales, and penguins were classified as swimming creatures. This type of classification was often based on the principle that creatures possessing analogous organs should be classified together. Analogous organs are organs that have the same function. The fins of fishes and the flippers of whales and penguins are analogous organs because they are all used for swimming. The wings of birds, bats, and insects are analogous organs that make flying possible. As more knowledge was gained about the anatomy of living things, it became apparent that similarities of habitat and of analogous organs were often rather superficial. The fact that bats have fur and nurse their young, birds have feathers and lay eggs, while insects are cold-blooded and have no internal skeleton suggested that these organisms differ from one another in more important ways than they resemble one another. An appreciation of the truly significant ways in which organisms resemble or differ from one another enabled the Swedish naturalist Carolus Linnaeus to found the modern system of classification. In 1753 he published a classification of the plants which was followed, in 1758, by a classification of the animals. For this work he is often called the father of taxonomy, the name given to the study of classification. His system of classification is fundamentally the system we use today. It is based on the principle of homology. Homologous organs are organs which show the same basic structure, the same general relationship to other organs, and the same pattern of very early growth. They need not, however, share the same function. An examination of the bones of the whale's flipper, the bat's wing, and man's arm reveals the same basic pattern (Fig.2-2). Furthermore, all these appendages are found in the same part of the body and develop in similar ways. They are homologous organs, although they are used to carry out quite different functions. Linnaeus felt that the difference in function was trivial, while the homology of the organs provided a sound basis for grouping these animals together. Why is classification based upon homology so significant? The answer to this question was not given until 1859 when Charles Darwin published his theory of evolution, According to Darwin, a classification based upon the presence of homologous organs is a classification based upon kinship. He felt that all creatures sharing homologous organs is a classification based upon kinship. He felt that all creatures sharing homologous organs are related to one another, having inherited their homologous organs from a common ancestor. Thus man, the bat, and the whale all had a single ancestor who possessed the basic forelimb structure that these creatures possess - although obviously in a quite modified form - today. Now, do a concept map of this material without referring to the passage. This will give you practice in remembering, and will show you exactly how much you know and don't know. It will also provide you with a solid basis for thinking critically about the topic.