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I. Taxonomy

I. Taxonomy. 1. Presently, there are considered by most taxonomists to be 6 kingdoms. These kingdoms are: Archaebacteria, Eubacteria, Protista, Fungi, Plantae, and Animalia.

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I. Taxonomy

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  1. I. Taxonomy

  2. 1. Presently, there are considered by most taxonomists to be 6 kingdoms. These kingdoms are: Archaebacteria, Eubacteria, Protista, Fungi, Plantae, and Animalia. • 2. These kingdoms have been determined after much study of physiological, structural, biochemical, and genetic characteristics.

  3. 3. The 6 kingdoms are then broken down into subdivisions called taxa. A seven level hierarchy of taxa is commonly used: • Kingdom • Phylum • Class • Order • Family • Genus • Species

  4. 4. Organisms are commonly named by a system referred to as binomial nomenclature. It utilizes the genus and species name for the organism. • 5. Examples include: • Homo sapiens (human) • Pisum satium (garden pea) • Felis domesticus (house cat)

  5. 6. A dichotomous key is a tool using specific observable traits in order to identify organisms. For each trait, the key lists 2 contrasting options. • 7. Phylogenetic trees are used to show the descent of a species from its ancestors. Structural and chemical homologies indicate close evolutionary relationships.

  6. 8. The present taxonomic system is subject to change as more genetic and biochemical information is gained. • 9. Recently, 1990, Carl Woese used the structural differences in rRNA to create three domains from the 6 kingdoms of life. They are: • Archae or “ancient bacteria, extremophiles” • Eubacteria or “true bacteria” • Eukarya – single cell or multicellular organisms with nuclei

  7. II. Theories of evolution

  8. 1. Jean Lamarck (1744-1829) proposed the idea that systems and body structures develop in response to use. He also felt that those structures in “disuse” eventually disappeared. Lamarck also believed that acquired characteristics could be passed on from parent to offspring.

  9. 2. August Weismann (1834-1914) disproved Lamarck’s theory of acquired characteristics inheritance. He cut off the tails of mice for 25 generations. All offspring continued to have long tails!

  10. 3. Charles Darwin (1809-1882) developed the theory of natural selection. He said that large numbers of new plants and animals are produced by nature. Many of these do not survive because nature “weeds out” weak and feeble organisms by killing off those that cannot adapt to changing environmental conditions. Only the strongest and most efficient survive and produce progeny.

  11. 4. A weakness of Darwin’s theory was that he did not explain the source, or genetic basis, for variations. He did not distinguish between hereditary and nonhereditary variations.

  12. 5. Hugo DeVries (1848-1935) explained variations in terms of mutations. This was later shown to be inaccurate because spontaneous mutation rates are very low and most are harmful. However, the idea got biologists looking for the causes of variation at the DNA level.

  13. 6. Modern ideas to explain variations and evolution: • a. Genetic recombination due to sexual reproduction • b. Gene flow or movement of new genes into a population (groups of organisms of the same species). • c. Genetic drift is a change in a gene pool that takes place in a population as a result of chance.

  14. d. Random mutations • e. Speciation is the forming of one or more new species from a species already in existence. This happens when a population becomes divided and part of the original species continues life in a new habitat, geographical isolation.

  15. III Principles of the modern theory of evolution

  16. 1. Evolution concerns the orderly changes that have shaped the Earth and that have modified the living species that inhabit the Earth. • 2. Inorganic evolution refers to changes of the Earth’s surface and interior. • 3. Organic evolution refers to changes that have taken place in living organisms.

  17. 4. Evidence that evolution has occurred in living things is provided by many sciences and includes facts from the geological record, the study of fossils (windows of the living past), evidence from cell studies and biochemistry, comparative anatomy and comparative embryology.

  18. 5. The age of the Earth has been estimated to be between 4.5 and 5 billion years old by the process of radioactive dating. This process involves using the half-life of an element and assumes that this half-life is not different than in the past.

  19. 6. Evolution is thought to have occurred by either gradualism or by punctuated equilibrium. • 7. In gradualism the change over time is slow and steady • 8. In punctuated equilibrium a species shows long periods of stability followed by sudden change. • 9. Most evolutionists believe punctuated equilibrium is most frequent.

  20. 10. Homologous structures have similar structure and embryological development, but different forms and functions as in a bat’s wing and a human arm. These structures indicate common ancestry. • 11. Analogous structures have similar form and function but different internal structure. These structures do not indicate common ancestry.

  21. 12. Vestigial structures are structures that are thought to have had a function in the past. However, they are not presently recognized to serve any purpose. Examples include the human appendix, the wings of an ostrich, and the human tailbone (coccyx).

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