Natural Selection

Natural Selection

1. Darwin's Theory

   • Different organisms in a species have genetic variation
   • Individuals best adapted to the environment are more likely to survive
   • Surviving individuals are more likely to breed
     • Creating offspring with best adaptations
   • The best characteristics are passed on to the next generation
   • Controversy
     • Inconclusive evidence
     • Challenged religious belief of God's creation
     • Idea of genes had not been discovered
   • Alfred Russel Wallace
     • Had similar ideas to Darwin
     • Both spent time on islands
     • Both produced joint writings

2. Modern Biology

   • Discovery of genes
     • How traits are inherited
   • Evolutionary biology
     • How organisms have adapted over time
     • Evidence
       • Fosslis
         • Show gradual change in organisms over time
         • Can show how species are related
           • Pentadactyl Limbs
             • Five digits/fingers
             • Found in many species
         • Formation:
           • Casts around soft materials
           • Preservation
             • In conditions where decay is not possible
               • Glaciers
                 • Extreme, low temperatures
               • Peat bogs
                 • Extreme acidity
           • Mineral Replacement
             • Hard parts of organisms replaced by minerals
               • Leave behind rock-like substance after decay
         • Examples
           • Ardi
             • Oldest human fossilised remains
             • 4.4 million years old
             • Ardipithecus ramidus
           • Lucy
             • 3.2 million years old
             • Australopithecus afarensis
           • Leakey
             • Most recent discoveries
             • 1.6 million years old
         • Stone Tools
           • More complex tools = bigger human brains
             • Basic tools - 2.6 million years ago
             • Complex tools - 1.6 million years ago
           • Carbon Dating
             • Shows when the stone was formed
               • Not when the tool was built
             • Determine how deep it was buried
               • Deeper = older
             • Use known dates of other items/fossils from that level
             • Compare design to other already dated stone tools
         • Incomplete record
           • Earlier species were soft-bodied
           • Geological activity destroyed some evidence
       • Antibiotics
         • Antibiotic Resistance
           • Bacteria reproduce rapidly
           • Mutations arise during reproduction
           • Some mutations may be antibiotic resistance
           • This will represent a new resistant strain
             • If treated with antibiotics, the bacteria will survive and reproduce
             • No treatment, and no human immunity
         • Development is slow and costly
         • Must only be prescribed for serious infections
         • Patients must complete the full course

3. Classification

   • 3 domain system
     • Proposed by Carl Woese
     • Based on chemical analysis
     • Archaea - primitive bacteria
       • Mostly extremophiles
     • Bacteria - true bacteria
     • Eukaryota - organisms with complex sub-cellular structures
   • Linnaean classification system
     • Devised by Carl Linnaeus
     • Based on structure and characteristics
     • Kingdom
     • Phylum
     • Class
     • Order
     • Family
     • Genus
     • Species

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