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Louisiana State University
Biological Sciences
BIOL 1202

Chapter 22 Descent with Modification A Darwinian View of LifeWhat is Evolution and AdaptationEvolution two main ideasoChange over time of the genetic composition of a populationoDescent of modern organisms with modification from preexisting organismsEvolutionary adaptationoAccumulation of inherited characteristics that enhance organisms ability to survive in specific environmentsPreDarwinian Theory of EvolutionLamarckoUse and disuseBodies of living organisms are modified through the use or disuse of partsoInheritance of acquired characteristicsThese modifications are inherited by offspringCatastrophism Gradualism and UniformitarianismCuviercatastrophismoCatastrophes caused extinct species and strataHutton gradualism and Lyell uniformitarianismoGradualism slow natural forces wing water earthquakes volcanoes caused geological formations not catastrophesoUniformitarianism the mechanisms of change that are constant over timeoObservations of geological formationsrates processes occurs earth much older than a few thousand yearsEvolution in a Historical Context Figure 222Evolution by Natural SelectionDarwin and Wallace developed the theory independentlyDarwinvoyage of the beagleWallaceBritish naturalist in IndonesiaDarwins Focus on AdaptationFigure 226Natural SelectionThe unequal survival and reproduction of organisms due to environmental forces resulting in the preservation of favorable adaptationsProcess selects from what is available in the gene poolNew characteristics are not created on demandArtificial SelectionSelective breeding of organisms to encourage the occurrence of desirable traitsProvides evidence for natural selectionFigure 229Trees versus scale naturaearistotles scala naturaeoladder of nature pg 453Evolution not about climbing ladder of nature from lower to higherEvolution is a bush with lineages branching from one anotherConcept 223 evolution is supported by an overwhelming amount of scientific evidenceWithin a few weeks of treatment with the drug 3tc a patients HIV populations consists almost entirely of 3tc resistant virus How can this best be explainedoD A few drug resistant viruses were present at the start of treatment and natural selection increased their frequencyNatural selection and HIV resistanceStart with different variants of HIV particlesHomologous and analogous structuresHomologousoStructures or other attributes in different species that resemble each other structurally but not necessarily functionally because of common ancestryAnalogousoStructures that are similar in function but not in structure and developmental and evolutionary originHomologous structures mammalian forelimbs 2214Homologous Structures Vertebrate embryos figure 2215All vertebrates share similar developmental genesDifferences arise by some genes being switched on or off at varying times during developmentHomologous structures biochemistry and molecular biologyDNA is universal genetic materialall life forms use approximately the same 20 amino acids to make proteinsall use ATP as the primary form of cellular energyall use RNA and ribosomes to make proteinConvergent evolutionsimilarity between 2 organisms structures or molecules due to independent evolution along similar lines rather than descent from a common ancestoranalogous structures are the result of convergent evolutionoExamples bat wing and butterfly wingoSimilar in function but not in structure
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