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Evolution Theories and Evidence 1 Evolution An orderly succession of changes. Biological evolution is the change of populations of organisms over generations. Came from a common ancestor 2 Lamarck’s Theory One of the first to propose a hypothesis of species modification. 3 Lamarck’s Theory Proposed that species evolve over time. Similar species descended from a common ancestor. 4 Lamarck’s Theory (cont’d) Incorrectly hypothesized that species modification is the result of acquired traits and that these traits can be passed on to offspring. Acquired traits: one not determined by genes, but arises during an organism’s lifetime as a result of the organism’s experience or behavior. 5 Lamarck’s Theory (cont’d) Example: •Lamarck’s theory said that webbed feet of water birds resulted from repeated stretching of the membrane between the toes. 6 Lamarck’s Theory (cont’d) •Over time, this produced a broad webbed foot, at trait that would be preserved by reproduction (offspring of parents with webbed feet would have webbed feet as well). 7 Lamarck’s Theory (cont’d) •Another example: giraffes 8 Lamarck’s Theory (cont’d) Lamarck’s hypothesis was widely attacked and was easily disproved. 9 Darwin’s Theories 50 years later (1809-1882) Began his work on evolution when employed as a naturalist for a voyage of the H.M.S. Beagle. 10 Darwin’s Theories 11 Darwin’s Theories Found evidence of species modification in both modern and extinct species. 12 Darwin’s Theories (cont’d) His ideas about evolution and natural selection are summed up in two theories: Descent with Modification Modification by Natural Selection 13 Darwin’s Theories (cont’d) Descent with Modification Newer forms appearing in the fossil record are actually the modified descendents of older species. •Example: Galapagos finches (13 Species) •Each had a distinct bill for eating. 14 Darwin’s Theories (cont’d) All species had descended from one or a few original types of life. This explained the observation that organisms give rise to others similar to themselves. •“Origin of Species” 16 Darwin’s Theories (cont’d) Modification by Natural Selection Natural selection is the principal driving force behind evolution. Environment may affect individual organisms in a population in different ways, because individuals of a species are not identical. 17 Darwin’s Theories (cont’d) Some organisms have traits that make them better able to cope with their environment. Organisms with a great number of favorable traits tend to leave more offspring than organisms with fewer beneficial traits. Different degrees of successful reproduction: natural selection. 18 Darwin’s Theories (cont’d) If a trait both increases the reproductive success of an organism and is inherited, then the trait will tend to be passed on to many offspring. A population of organisms adapt to their environment as their proportion of genes for a favorable trait increases. 19 Darwin’s Theories (cont’d) Resulting change in the genetic makeup of a population is evolution. A single organism’s contribution to the next generation is termed fitness. A favorable trait gives an organism that has it an adaptive advantage. 20 Darwin’s Theories (cont’d) The environment “selects” the traits that will increase in a population. •Example: Peppered Moths 21 Peppered Moths Darwin’s Theories (cont’d) Selection conditions change as the demands of the environment change. •If change is too fast, populations may not adapt fast enough and will become extinct. 23 Evidence of Evolution Evidence supporting evolution is found in the body structures of living organisms. 24 Evidence of Evolution (cont’d) Homologous features: similar features that originated in a shared common ancestor. 25 Evidence of Evolution (cont’d) Example: forelimbs in human, bat, penguin, and alligator •Look different •Vary in function •Very similar in skeletal structure •Derived from the same embryological structures 26 Forelimbs of Vertebrates Evidence of Evolution (cont’d) Analogous features: serve identical functions and look somewhat alike. Very different embryological development May be different in internal anatomy. 28 Evidence of Evolution (cont’d) Example: wings in birds and insects. •Share a very remote ancestor •Wings evolved independently and differently in more recent ancestors. 29 Evidence of Evolution (cont’d) Vestigial features: serve no useful function. Examples: human appendix and tailbone Were useful to an ancestor, but no longer useful to modern organisms. 31 Evidence of Evolution (cont’d) Evidence that the feature was functional in some ancestors of the modern organism. Modern organism with such feature, probably shares common ancestry with an organism that has a functional version of that feature. 32 Evidence of Evolution (cont’d) Similarities in Embryology Similar embryological development among species indicates a common evolutionary history. 33 Evidence of Evolution (cont’d) • Early stages of different vertebrate embryos are very similar. 34 Evidence of Evolution (cont’d) Similarities in Macromolecules: Similarity in DNA, RNA, and proteins indicates a common evolutionary history. •The more similar the macromolecules, the more closely related the species are thought to be. 35 Patterns of Evolution Coevolution: two or more closely associated species change in response to each other. Example: plants and their pollinators 36 Patterns of Evolution (cont’d) Convergent Evolution: organisms that are not closely related resemble each other because they have responded to similar environments. 37 Patterns of Evolution (cont’d) Example: sharks and porpoises appear very similar, but are not closely related. Environment selects similar phenotypes. Analogous features associated with convergent evolution. 38 Patterns of Evolution (cont’d) Divergent Evolution: related populations become less similar as they respond to different environments. Can ultimately result in a new species. 39 Patterns of Evolution (cont’d) Adaptive radiation:many related species evolve from a single ancestral species. • Example: Galapagos finches 40 Patterns of Evolution (cont’d) Process can be sped up artificially through artificial selection. •Example: dog breeding. 41