ii.theories of evolution a. development of theories

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  • Theories of EvolutionA. Development of Theories

  • Observations Lead to a Question13 species of finches unique to Galpagos islandsALL most closely resemble 1 finch species living on the South American mainland. The hypothesis: the islands were colonized by a single finch species that strayed from the mainland -- This bird adapted differently to the different habitats on each islandkey characteristic of the finches -- beaksadapted to the foods available on the each islandHow did these different beaks arise? -- through natural selection

  • 1. Jean-Baptiste Lamarck (1744-1829) First person to suggest that life evolvedThe law of Use and DisuseInheritance of acquired characteristics

  • Lamarck believed that giraffes stretched their necks to reach food. Their offspring and later generations inherited the resulting long necks

  • Charles Darwin

  • 2. Darwins Theory: Natural Selection (Based on his observations)Variation exists within all speciesPopulations always tend to increaseThe amount of resources is limitedThere will be a struggle for the available resourcesOrganisms who are most fit will live longer and have more offspring. (The offspring will inherit advantageous traits)

  • Most giraffes used to have short necks, but some had slightly longer necks. When the food on the lower branches was eaten, many of the giraffes with shorter necks died of starvation, leaving the ones with slightly longer necks to survive and reproduced. Through many generations, the giraffes with longer necks became the most common.

  • Pesticides = Natural Selection in ActionPesticides: poisons used to kill insects 100s of insects have developed pesticide resistanceSurvivor bugs after the first pesticide treatment had genes that somehow enabled them to resist the chemical attack.Survivors offspring inherited the genes for pesticide resistance. A pesticide does not create resistant individuals, but selects for resistant insects that are already present in the population.

  • Artificial Selectionselective breeding of plants / animals produce offspring w/genetic traits that humans valueplant breeders improve traits -- grain production, disease resistance, protein contentanimal breeders select for growth rate or temperamentBreeders play the role of the environment, allowing only those plants or animals with desired traits to reproduce.

  • Artificial SelectionDarwin observed that artificial selection could produce a great deal of change in a species in a short time. He reasoned that over thousands of generations, natural selection could also cause major change. Artificial Selection = humans choosenatural selection favors traits that benefit the organisms in their particular environmentenvironmental conditions do the "selective breeding."

  • 3. Origin of VariationGenetic Recombination (Sexual reproduction. Meiosis, Crossing over and random fertilization)Mutation (Produces New Genes)

  • B. Mechanisms of Evolution1. Species and PopulationsEvolution cannot be seen in an individual because their genes do not change.a) Evolution is a change in the genetic make up of a population b) Gene Pool- all the different alleles (gene forms) in a population2. Hardy-Weinburg principleGene Pool

  • 2.

  • Population Genetics Or Fun with Hardy-Weinburg! The Math!Let P = the frequency of Dominant Genes in a populationLet q = the frequency of Recessive genes in a population Therefore:P + q = 1All the dominant genes + all the recessive genes = all the genes

  • Individuals can be:GenotypesHardy-Weinburg NotationHomozygous DominantPP or P2HeterozygousPq + qP or 2PqHomozygous Recessiveqq or q2pqpqP2PqqPq2Therefore:P2 + 2Pq + q2 =1All the Homozygous Dominant + All the Heterozygotes + All the Homozygous Recessives = All the PopulationWith these formulas, you can solve all Hardy-Weinburg problems

  • C. Factors which Change Genetic Equilibrium (ie. Cause Evolution)1. Natural Selection: Favoring one genotype over another. Ex. H. B. Kettlewell

  • In England, before the industrial revolution, tree bark was a lighter color and lighter moths out numbered darker moths 9:1

  • Coal caused the tree bark to darken during the industrial revolution. The darker moths then numbered the lighter moths 9:1

  • Types of Selectiona) Directional Selection- constant genetic change of one type. Ie. Giraffes necks getting longer. Dinosaur size increasing

  • b) Stabilizing Selection- Selection that favors the average and eliminates the extremes. The population becomes more alikeTypes of Selection

  • Siberian Huskies sled dogs (35-60 lbs.)Too heavy too slow and potentially sink in snowToo light not strong enough to pull sledsThe population all becomes similar to each other

  • c) Disruptive selection- Selection that favors the extremes and eliminates the average. Population becomes more different. This can lead to new speciesTypes of Selection

  • Meteor hit Earth 65 myaFood was depleted, dust blocked the sun, tsunamis and wildfires were plentiful.Larger (average) animals who need lots of oxygen and food, died out quickly.

  • Types of Selection

  • C. Factors which Change Genetic Equilibrium (ie. Cause Evolution)Gene flow- Movement of organisms in or out of a populationMutation- change in a gene form that is unequal. Ie. Change form gene A to a more than a to A.Genetic Drift- change in gene frequency due to random chance (some genotypes may mate more than another just due to chance)Isolation- separation of a population so it cant interbreed. Either genetic or geographic

  • Patterns of EvolutionDivergent evolution-Two separate species becoming more different due to different selective pressures in different environments (human foot vs. ape foot)Adaptive Radiation- process by which species adapt to a variety of habitatsSpeciation- formation of two separate species from one


  • 2. Convergent Evolution- the process by which distantly related organisms become more similar due to similar selective pressures in similar habitats


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