Evolution (PCB 4674). Chapter 2. The evidence for evolution

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EVOLUTION/LECTURE1 "Species have changed through time and are related by descent from a common ancestor" This statement is the backbone of the theory of evolution as exposed by Charles Darwin. 1.8. In this chapter we will explore first data that challenges the three main statements of the Theory of Special Creation indicated in 1.5 (i.e. species are independent, immutable and recent). In the second half of the chapter we will introduce several data drawn from different fields of scientific inquiry that supports predictions of the Theory of Evolution 2.- Relatedness of life forms and homology 2.1.- The Theory of Special Creation contends that each species was created independently. In contrast the Theory of Evolution contends that organisms are related by common ancestry. 2.2.- Results from the fields of comparative anatomy and embryology demonstrate that fundamental similarities underlie the obvious physical differences among species. Early researchers called this phenomenon homology. Two good examples can be found in the vertebrate skeletons and in flower organs. If species share common ancestors they also should share many characters of their ancestors. Homologous characters reflect the common ancestry of species 2.3.- Vertebrates forelimbs are used for different functions, but they ALL HAVE the same sequence and arrangement of bones. Figure 2.1.a.: Vertebrate homologous bones. Homologous bones are colored or shaded in the same way, and are labeled on the human arm file:///E|/CH2-EVIDENCE-SPRING-2008/CHAPTER2_SPR_2008.HTML[12/8/2011 11:22:00 AM]
EVOLUTION/LECTURE1 2.4.- Likewise orchid flowers are diverse in size and shape, but are comprised of elements that are similar in structure and orientation (Fig 2.1.b) Figure 2.1.b.: Homology among flower elements of two orchid species 2.5.- Homologies can also be found at developmental, structural and embryonic levels. For instance the amino acid sequences encoded by a gene involved in the development of the eye exhibits 90% similarities among vertebrate and invertebrate organisms (Fig. 2.2.a) Figure 2.2.a.: Genetic homologies: The amino acid sequences of a section called the homeodomain in a protein involved in the development of the eye. Dots indicate the same amino acid as the one above 2.6.- Advances in molecular genetics have revealed other fundamental similarities among organisms. One of the most spectacular is the genetic code. With a few minor exceptions, all organisms studied to date use the same nucleotide triplets, or codons, to specify the same amino-acid-bearing RNAs (Figure 2.2.b). Figure 2.2.b.: Genetic homologies: The genetic code; in almost every organism studied, the same nucleotide triplets, or codons, specify the same amino acid bearing transfer RNAs file:///E|/CH2-EVIDENCE-SPRING-2008/CHAPTER2_SPR_2008.HTML[12/8/2011 11:22:00 AM]
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Evolution (PCB 4674). Chapter 2. The evidence for evolution

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