Evolution

Evidence
1. Fossil Records
  1. Sequence of changing fossils from layers of rock strata
  2. Carbon dating (radioisotopes)
  3. Phylogenic tree can be made
    1. e.g. Equus
  4. (-) Gaps in records
    1. fossils only form in environments that prevent decay
2. Selective Breeding
  1. Breed differentiation has occurred in domesticated animals
    1. (-) Human rather than natural selection
    2. Evolution in short time-period
    3. e.g. Dogs
3. Structures
  1. Homologous Structures (Divergent Evolution)
    1. Similar structure, different function
    2. Often formed similarly in embryo
    3. e.g. Pentadactyl limb
      1. same bones in similar positions "unity of type" - Darwin
        i.e. radius and ulna attached to humerus
      2. “Adaptive radiation”
      3. different purposes
        swimming, running, digging, jumping
    4. Rudimentary/vestigial organs
      1. e.g. human appendix, snake hip bones
  2. Analogous Structures (Convergent Evolution)
    1. Similar function, different origin
    2. e.g. fish and whale tails
4. Patterns of Variation
  1. Continuous variation
    1. across geographical range
      1. e.g. human skin colour
  2. Discrete variation
    1. e.g. industrial melanism
  3. therefore, causes divergence
Speciation
1. Divergence in the gene pool of a population
  1. can be confirmed if two diverged populations are merged and do not interbreed
2. Models
  1. Phyletic Gradualism
    1. many intermediate forms between species
  2. Punctuated Equilibrium
    1. long periods of relative stability (stasis) and then periods of rapid evolution
      1. Mass speciation event - natural disaster causes extinction and new species can erupt to take advantage of resources
    2. explains gaps in fossil records
    3. incited by sudden environmental changes
  3. e.g. Galapagos finches
    1. Gradualism: Darwin observes Adaptive radiation
    2. Punctuated Eq.: Peter and Rosemary Grant observed drought
      1. in drought, bigger beaks survived
        Directional natural selection
3. Causes
  1. Change in allele frequencies in populations
    1. Gene pools contain all the genes and the different alleles of a population
    2. Theoretical: Hardy-Weinberg Equilibrium formula
    3. Actual: ALFreD database
    4. Genetic equilibrium - when all members of a population have an equal chance of contributing to the future gene pool i.e. same chance of reproduction
      1. Heritability is the proportion of variation that is due to genes
  2. Reproductive Isolation
    1. Sympatric
      1. Temporal
        e.g. flowering at different time
      2. Behavioral
        e.g. mating displays change
    2. Allopatric
      1. Geographical
        i.e. no interaction with other populations
        esp. Endemic species
4. Polyploidy
  1. Causes
    1. Autopolyploidy
      1. single species, problem in meiosis
    2. Allopolyploidy
      1. hybrid
  2. Organism that has more than two sets of homologous chromosomes
    1. diploid and haploid gamete fuse
      1. organism not sterile since there will always be a chromosome to pair with if it mates with another polyploid or self-pollinates
  3. Effects
    1. Instant speciation when only polyploids can reproduce together
    2. evolution for angiosperms that clone themselves
      1. e.g. Allium
    3. desirable crops can self-pollinate
  4. e.g. Red viscacha has 102 chromosomes, 4n=112 then shed some
Mechanisms
1. Natural Selection
  1. Patterns of Natural Selection
    1. Stabilizing selection
      1. mean of the normal curve is preferred
        e.g.. birth size of humans, # of eggs hatched
    2. Directional selection
      1. shift to one extreme due to a selective pressure or environmental resistance
        e.g.peppered moths, beak sizes, antibiotic resistance
        mutations occur that make the bacteria resistant to antibiotics
        exchanging of plasmids
    3. Disruptive selection
      1. the mean is undesirable
        tends to drive speciation most because offspring occupy divergent niches
        e.g. Red crossbill, small or large fish
  2. i.e. competition
  3. Causes
    1. variation within a species
      1. Mutations
      2. meiosis (independent assortment, crossing over)
      3. sexual reproduction and random fertilization
      4. plasmid transfer
    2. populations produce more offspring than an environment can support
      1. environmental resistance
      2. survival of the fittest
  4. Effects
    1. adaptation to make an individual more suited to its environment
      1. occupies a niche
    2. Only animals that reproduce pass on their genes to offspring
    3. Natural selection increases the frequencies of beneficial alleles
      1. "progressive change"
    4. Organisms that reproduce more often evolve faster
2. Genetic Drift
  1. i.e. geographical separation
3. Genetic Flow
  1. i.e. migration of populations
4. Selective Pressures
  1. i.e. extenuating factors
The cumulation of changes in the heritable characteristics of a population

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Evolution

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