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Lamarck and Darwin

  • Lamarck's Theory
    • Altered environment changes of phenotype
    • This happens DURING LIFE (after organism is born)
    • Change is passed on to its offspring
  • Darwin's Theory (this is the accepted theory)
    • Phenotype randomly changes during sexual reproduction
      • Mutation and recombination of alleles changes genes/phenotype
      • This allows variation (in appearance, behaviour, ...) which is essential for natural selection
      • Variation may be beneficial or harmful
    • Resources (food, light) in the environment are limited
    • Beneficial variation allow adaptation to the environment
      • Organisms are more likely to make full use of resources (food, light)
      • Increased survival and reproduction
      • Successful alleles are passed on to their offspring
    • Harmful variation
      • Organisms have limited access to resources/too much competition
      • Shorter survival and reproduce less often
      • Phenotype is not passed on
      • Organisms with the harmful characteristic eventually die out
    • Organisms over-reproduce allowing more random changes/variation
      • Higher chance that a better phenotype will develop

Natural selection

  • Responsible for development of new species from existing ones
  • New environment + mutationadaptation
    • Affects survival rate of phenotype before reproduction
      • Otherwise population would become extinct
    • Organisms better adapted survive, reproduce, and pass on their alleles/genes
    • Allele frequency of the advantageous gene increases
    • Changes frequencies of alleles in gene pool / phenotype in population
  • Stabilising selection
    • Natural selection favours "average" organisms best adapted to that environment
    • Organisms with extreme forms of characteristics/mutations are selected against
    • Heaviest and lightest babies have highest mortality
    • Less likely to survive, reproduce, pass on their alleles
    • [Graph] Normal distribution curve with thinner bell-shaped curve
  • Directional selection
    • Natural selection favours organisms with one extreme form of a characteristic
    • Pesticide resistance (warfarin - poison used to kill rats)
      • Resistant rats → require a lot of vitamin K → disadvantage / selected against → small population
      • New environmental effect: warfarin → kills normal rats
      • Resistant rats survive, reproduce, pass on resistance gene
      • New population forms by directional selection
    • Antibiotic resistance (penicillin resistance)
      • Resistant bacteria / unnecessary enzymes / selected against
      • New environmental factor: penicillin → kills normal bacteria
      • Resistant bacteria survive, reproduce, pass on resistance gene
    • [Graph] Bell-shaped curve shifts to the right


  • Splitting of one into more species / transformation of one into a new species over time
  • Emigration/immigration moves alleles between populations
  • Changes allele frequency by genetic variation in meiosis

Reproductive Isolation

  • Premating
    • Habitat isolation: populations inhibit different local habitants within one environment
    • Temporal isolation: same environment but are reproductively active at different times
    • Behavioural isolation: two populations have different courtship patterns
    • Geographical separation: populations inhabit different islands, continents, ...
  • Postmating
    • Gametes mortality: sperm cannot reach or fertilize egg
    • Zygote mortality: fertilisation occurs, but zygote fails to develop
    • Hybrid sterility: hybrid survives (viable) but is sterile and cannot reproduce (no meiosis)
    • Hybrid inviability: incomplete development

Allopatric Speciation (geographical isolation)

  • Physical barrier (H2O, mountains, dessert) divides a population
  • Two different environments (abiotic, biotic)
  • Natural selection
  • Genetic drift changes genotype and phenotype
  • Two populations evolve separately
  • Reproductively isolated / 2 distinct species

Sympatric Speciation (reproductive isolation)

  • Genetic isolation by mutation / reproductively isolated / but inhibit same habitat
  • Drift can cause further divergence between isolated gene pools
  • Hybridisation in plants
    • Offspring produced from parents of two different species
    • Chromosomal number doubles / polyploidy
    • New species is reproductively isolated by a postmating mechanisms
  • Can only reproduce with other polyploids, backcrosses with (2n) parents are sterile

Fossil dating

  • Radioactive isotopes
    • Slowly decay over time
    • Measured by using its half-life
    • Not affected by temp, pressure, ...
  • Stratigraphy
    • Fossil contained within a rock can be dated by assessing its number of layers
    • The older the rock, the more layers present, the older and deeper the fossil
    • Limitations
      • Earthquakes or volcanic eruptions may displace fossils within rocks
      • Fossil may be washed out and found at a different place
  • Potassium-argon dating
    • Decays into 40Ar and 40Ca
    • Limitation: found in volcanic rocks only
  • Carbon dating
    • Radioactive carbon (14C) is found in CO2
    • CO2 is used and stored by plants
    • Animals eat plants and store 14C in their body
    • Limitation: 14C is decayed after 50 000yrs - cannot be used in samples older than that