ch 13

• Evolution


  A population's allele composition (frequencies) change over time
• Agents/factors that evolution relies on


  • Mutations (new alleles)
  • Migration (gene flow)
  • Genetic drift
  • Bottleneck and founder effect
  • Natural and sexual selection
• Microevolution


  Agents of evolution change allele frequencies/phenotypes in populations over shorter time scales (i.e. a few generations)
• Microevolution


  • Beneficial alleles maintained; unfavorable/harmful alleles eliminated
  • Causes small-scale changes to species (ex. Peppered moths, antibiotic resistance in bacteria, mouse fur phenotype, etc.)
• Macroevolution


  Genetic and phenotypic changes over long evolutionary time scales (i.e. millions of years) that result in new species and higher taxa
• Macroevolution


  • If isolated populations evolve (change) enough to where they are no longer able to reproduce, they are considered two separate species
  • Over billions of years, organisms have changed so much from ancestral forms to warrant classification in higher taxa (i.e. Domain, Kingdom, Phylum, etc.)
• Evidence of evolution


  1. Population separation

  2. Different evolutionary pressures

  3. Phenotypic variation
• Evidence of evolution


  • Fossil evidence
  • Biogeography
  • Anatomical/morphological comparisons
  • Embryonic development
  • Molecular (DNA/RNA/Protein) comparisons
• Paleontology


  Study of ancient life from fossil remains
• Paleontology


  • Provides most of our understanding of the different types of ancient lifeforms on Earth
  • Fossils: physical remains of ancient organisms preserved in layers of rock
  • Transitional fossils: very rare fossils that clearly show anatomical transitions from ancient life forms into more modern forms
• Transitional fossil


  • Tiktaalik- fossil evidence of transition from fully-aquatic animals to terrestrial tetrapods

  
• Sedimentary rocks


  Layered rocks formed from sand/mud sediments
• Sedimentary rocks


  • Associated with wind and water erosion of rock
  • Sometimes, organisms would be rapidly buried and preserved in the sediments→ fossils
• Stratification


  Rock layering with surface layers more recently deposited and older and older layers deeper from surface
• Geologic timescale


  • Life begins (~3.8 bya)
  • Cambrian explosion (~540 mya)
  • Invasion of land (~470 mya)
  • Dinosaurs, ancient mammals, large trees in forests (~250-65mya)
  • Meteor kills dinosaurs leading to rise of mammals (~65mya)
  • Age of humans (~1.8mya-present)
• Body fossil


  Rapid preservation in ice, dry air, or tree sap

  
• Cast fossil


  Minerals in ground water replace the body parts and crystalize into rock in the shape of the organism
• Mold fossil


  Hard body parts make impression in sediments then degrade leaving behind their shape in the rock
• The fossil record is incredibly incomplete
• Reasons the fossil record is incomplete


  • Some never leave a fossil- soft bodied organisms
  • Erosion/movement of continental plates destroys rock layers
  • Fossils may be in hard-to-reach or poorly-studied places
  • Not all organisms lived in appropriate environments
• Relative dating


  Based on depth fossil found at. (Deeper= older)
• Absolute dating


  Age of rock layer determined with radiometric analysis (radioisotope half-life analysis)
• Radioisotopes


  Some unstable isotopes are deemed "radioactive" when the nucleus spontaneously decays into more stable daughter isotopes and ejects high-energy radiation
• Half-life


  The average time for half of the radioactive atoms to spontaneously decay into the stable product

  
• 14C


  Constantly produced in the atmosphere in reaction between cosmic rays and nitrogen, used to date "recently" deceased organisms
• 14C dating


  • 14C half-life= 5730 years; ~30,000 year dating ability
• Plate tectonics


  Tectonic plates- solid top layers moving on hot mantle

  
• Biogeography


  The study of species distribution
• We must consider ancient land formations/environmental conditions to better understand modern or ancient species distributions
• Biogeography


  • Closely-related flightless birds with wide global distribution
  • Wallace's line- clear difference between animals on the Malay archipelago along a particular line

  
• Homologous structures


  Anatomical structures that evolved in the common ancestor and passed to all resulting lineages
• Analogous structures


  Similar structures/traits due to shared selective pressures- NOT from a direct common ancestor
• Convergent evolution


  When two or more unrelated lineages of organisms evolve analogous structures and attain similar traits
• Vestigial character


  No apparent function in modern organism, but homologous to functional structures in other organisms
• Embryonic development


  • Early embryonic stages are very similar among diverse lineages of animals
  • Genetic programs developed in ancient common ancestors dictate early development
  • Species-specific gene expression patterns take over at later stages and determine each species' unique development
• Molecular clock


  Comparing gene/protein sequences to understand evolutionary change
• Before speciation occurs, all members of a population make up a single gene pool
• If we can estimate # of mutations per unit time, comparing # of DNA/protein sequence differences can reveal approximate time since divergence
• Molecular clock


  • Cytochrome c amino acid sequence differences between human and different eukaryotes reveal less differences between more closely related species (less time to change independently since species diverged)