Modern Theory of Evolution

• Once thought that creation was immutable (divinely designed)
• Earth was thought to be relatively young (Archbishop James Ussher of Armagh, 1650) and declared the Earth was created on Sunday October 23, 4004 B.C.
• Radiometric dating


  Indicates that the Earth is about 4.5 billion years old, and the universe is about 13 billion years old
• Radioisotopes


  Atoms that undergo radioactive decay (nucleus of an atom changes and releases a subatomic particle)
• Decay rates can be measured accurately
• Half-life


  When 50% of sample of parent isotope converted to daughter isotope
• Darwin's theory could not account for how species evolve or the source of variation
• Modern Evolutionary Synthesis


  Modern genetics and biology have been combined with Darwin's theory
• Evolution


  Changes in the gene pool of a species over time
• Natural selection


  Acts to favour some genetic combinations over other
• Under a set of specific conditions, a given gene pool (total of all alleles within a population) remains unchanged from generation to generation
• Key factors that can cause evolution

  • Chance fluctuations in small populations
  • Nonrandom mating
  • Genetic mutations
  • Migration
  • Natural selection
• Genetic drift


  A change in the genetic makeup of a population resulting from chance
• Bottleneck effect


  A dramatic, often temporary, reduction in a population size usually resulting in significant genetic drift
• Founder effect


  Genetic drift that results when a small number of individuals separate from their original population and find a new population
• Gene flow


  The movement of alleles from one population to another through the movement of individuals or gametes
• Mutations are the only source of additional genetic material and new alleles, arising as a result of unrepaired changes in DNA sequences or chromosome breakage and rejoining
• Types of mutations


  • Neutral
  • Harmful
  • Beneficial
• Mutations can also result in duplicate copies of genes
• Gametes that receive a chromosome that is missing a section will have a low chance of survival
• Gametes that receive a chromosome with duplicated genes are often viable. Extra copies can be beneficial.
• Gene duplication is a source of new genes. The extra copy is free to mutate and may gain a new function
• Studies suggest that humans, with genomes consisting of billions of bases, average 20+ mutations/individual (most are neutral mutations)
• Human population (now over 7 billion), is carrying around 100 billion genetic mutations
• Influence of mutations on evolution

  • Beneficial mutations are relatively rare but are favoured by natural selection and tend to accumulate in populations over time
  • Harmful mutations are more common than beneficial mutations but are selected against therefore have no influence on populations
  • Duplication mutations are often neutral and so do not immediately benefit the individual, but provide a source of new genetic material with the potential to evolve into new genes
  • Mutation rates are relatively low for individuals but can be numerous in populations overall
• Pseudogenes


  Vestigial genes that no longer code for a functioning gene
• Species distributions of 4 species match the arrangement of the Earth's land masses at the time the species were alive
• Plate Tectonics


  Theory that describes the large-scale movements and features of the earth's crust