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Evolution- Beliefs about the origin of life http://mysite.verizon.net/vzepz6a9/biorefwe b/evolutionhomework.html Beliefs about the origin of life Abiogenesis: life might arise spontaneously from nonliving material . Panspermia: life might arise from the molecules from outer space Autotroph hypothesis: The first living organism is an autotroph. Heterotroph hypothesis:life might arise from a chemical evolution. Heterotroph hypothesis: The classic experiment demonstrating the mechanisms by which inorganic elements could combine to form the precursors of organic chemicals was the 1953 experiment by Stanley Miller. He undertook experiments designed to find out how lightning--reproduced by repeated electric discharges--might have affected the primitive earth atmosphere. He discharged an electric spark into a mixture thought to resemble the primordial composition of the atmosphere. In a water receptacle, designed to model an ancient ocean, amino acids appeared. Amino acids are widely regarded as the building blocks of life. Evidences for Evolution 1. 2. 3. 4. 5. 6. 7. 8. Comparative Anatomy Vestigial Structures Comparative Embryology Molecular Biology Fossil record Taxonomy Artificial selection Biogeography 1. Comparative Anatomy Scientists often try to determine the relatedness of two organisms by comparing external and internal structures. Anatomical features in different species that point to a common ancestor are called homologous structures. For example, the flipper of a whale and a human arm seem to be quite different when looked at on the outside. But the bone structure of each is surprisingly similar, suggesting that whales and humans have a common ancestor way back in prehistory These sorts of structures, which have superficial similarities because of similarity of function but do not result from a common ancestor, are called analogous structures. bats and insects share a common ancestor, since both have wings. But a closer look at the structure of the wings shows that there is very little in common between them besides their function . 2. Vestigial Structures In addition to homologous and analogous structures, vestigial structures, which serve no apparent modern function, can help determine how an organism may have evolved over time. In humans the appendix is useless, but in cows and other mammalian herbivores a similar structure is used to digest cellulose 3. Comparative Embryology In general, the more closely related two species are, the more their embryological processes of development resemble each other 4. Molecular Evolution Two species that are closely related will have fewer genetic or protein differences between them . Certain genes or proteins in organisms change at a constant rate over time. 5. Fossil record Fossils are the traces of past life. They include footprints, burrows, worm casts. Most of the fossils are found embedded in or on rocks. Paleontology is the science of studying fossils. Relative age of the fossils can be determined by the geologists by examining the layers of the earth crust. And by the carbon dating methods in which radioactive isotope of C is examined. The time scale derived from fossil records is usually calculated from radioactive dating. For example in carbon-14 dating, the fact that the ratio of C14 to C12 is fairly constant (~ 10-12) in living organisms and that C14 is radioactive with a halflife of about 5730 years, would yield the age of the organism since its death (no more accumulation of C14) if we measure the leftover amount of C14 in the sample 6. Taxonomy The science of classification is taxonomy. Classification is the process of grouping the organisms according to their properties. Organisms are classified into larger groups. Species is the smallest one , kingdom is the largest one. Kingdom Phylum Class Order Family Genus Species 7. Artificial selection Artificial selection is to select the animal to reproduce. It is not randomly reproduction(natural selection). As a result of artificial reproduction some of the species are selected to reproduce and their numbers are increased. Horse, cereal grains important for agriculture, chicken 8. Biogeography Biogeography is the study of geographic distribution of life forms on earth. Biogeography has an influence on the adaptation of species to a certain area. In that way same species adapt to different areas in different ways and this causes variation. (adaptation) Accepted Rules for Evolution Allen rule The organisms living in cold areas have smaller extensions.( small ear, short tail) But organisms living in warmer areas have larger extensions for heat control.(large ear, long tail) Bergmann rule The organisms living in cold areas have smaller surface area/volume ratio.( big animals have small surface area but large volume) But organisms living in warmer areas have larger surface area/volume ratio.( small animals have large surface area but small volume) Dollo rule Evolution always preceeds onwards not backwords. Life begins in water and proceeds in land. Not goes back. Cope rule Vertebrates tend to increase their body size during evolution. (to store important molecules) Gloger rule The mammals and birds tend to be darker near the equatorial region. (protection against sun rays) Theories of Evolution 1. Lamarck: Use and Disuse 1809 The classic example used to explain Lamarckism is the elongated neck of the giraffe. According to Lamarck’s theory, a given giraffe could, over a lifetime of straining to reach high branches, develop an elongated neck. This vividly illustrates Lamarck’s belief that use could amplify or enhance a trait. Similarly, he believed that disuse would cause a trait to become reduced The second part of Lamarck’s mechanism for evolution involved the inheritance of acquired traits. He believed that if an organism’s traits changed over the course of its lifetime, the organism would pass these traits along to its offspring. 2. Darwin: Natural Selection Each species produces more offspring than can survive. The individual organisms that make up a larger population are born with certain variations. The overabundance of offspring creates a competition for survival among individual organisms. The individuals that have the most favorable variations will survive and reproduce, while those with less favorable variations are less likely to survive and reproduce. Variations are passed down from parent to offspring. Beagle’s trip 1831-1836 The competition that Darwin’s theory describes is sometimes called the survival of the fittest. Most particularly, he took interest in the islands’ various finches, whose beaks were all highly adapted to their particular lifestyles . The Genetic Basis for Evolution Variations exist in the individuals within a population. Those variations are passed down from one generation to the next. (inherited) If variations favour the survival of the organism then the organism who carries these variations will repoduce and fit to the environment. This is called adaptation. Development of New Species Speciation The scientific definition of a species is a group of organisms that reproduce within the group and produces fertile new organisms. As populations change, new species evolve. This process is known as speciation. Speciation is also called divergent evolution, since when a new species develops, it diverges from a previous form. All homologous traits are produced by divergent evolution. Speciation occurs when two populations become reproductively isolated . Allopatric speciation occurs when populations of a species become geographically isolated so that they cannot interbreed . Sympatric speciation is the result of a genetic isolation without a geographical barrier Over time, the populations may become genetically different in response to the unique selection pressures operating in their different environments. Eventually the genetic differences between the two populations will become so extreme that the two populations would be unable to interbreed even if the geographic barrier disappeared.