Mind map

Evolution

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Evolution

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