Evolution

Evolution

1. Origins of Life

   • Single Celled Life
     • 5am to 1pm (after heavy bombardment stops, life forms began to form).
     • Grew underground and moved to the surface. ex. Snotites, phelgmballs (acidophiles)
     • Dominated Earth: nothing else could survive due the hostile environment (Co2, H2S).
     • 9pm-11:59- higher levels of O2, ozone layer formed which allowed for life to form. Evolutionary Theory:

2. Evolutionary Theory

   • Charles Lyell
     • Forces acting on the Earth today are the same slow gradual process that have occurred in the past.
     • “Uniformitarianism”
     • ex. Floods are the same power as now.
   • Thomas Malthus
     • Population grew geometrically (exponentially) and food grows linearly (arthimathically)
     • At some point there will not be enough food to sustain the population.
     • Populations reached a carrying capacity (max. number of species)
     • Limited by: death, diseases, death, war etc.
   • Charles Darwin
     • Natural selection (Mechanism of Evolution)
       • Gradual process by traits becoming either more or less common in a population due to reproductive success.
       • “Survival of the Fittest”
         • Species with the best traits will be selected by the environment. These species will survive and reproduce. ex. more blubber on emperor penguins allow them to survive in cold environments.
       • "Decent with modification
         • Idea that life has once common origin and diversified to the forms we see on Earth today.
   • Jean-Baptise Lamarck
     • Inheritance of acquired characteristics
       • Characteristics that a organism acquired over their life would be passed on to the next generation.
         • Better adapted traits to an environment.
       • “line of decent” - fossils led to modern species.
       • ex. Giraffes long necks to eat food at the top. Body parts not used would eventually disappear- use and disuse.
   • Georges Cuvier
     • Species were shaped my sudden catastrophic events that happened in limited geographical areas.
       • Owls can turn their heads 360- A catastrophic event whipped out the population of owls and was repopulated by owls from a different area with the mutation.
   • Gould & Eldredge
     • Punctuated Equilibrium
       • Periods of stasis: little to no change in population
     • Periods of rapid change
       • Punctuated events
         • Selection of traits that best allows a population to survive this change.
           • Ex. Big shells for snails.

3. Introduction to Genetics:

   • Terms
     • DNA
       • genetic code stored in a molecule. responsible for everything.
     • Genes
       • segments of DNA that code for a specific trait ex. hair colour, eye colour, height.
     • Alleles
       • variations of a gene/trait ex. red, brown, blonde, black hair colour
       • Allele Frequency
         • the proportion of each allele present in a population for a trait. ex. number of S allele= 25, total alleles (S+s)= 50, AF is 25/50= 50%
     • Genotype
       • the alleles that code for a trait ex. PP, Pp, pp
       • Homoxygous
         • a genotype made up of two of the same alleles.
         • Heterozygous
           • a genotype made up of different alleles.
     • Gene Pool
       • all the alleles that exist in the population for a trait.
     • Phenotype
       • the appearance of the genotype ex. purple, white.

4. Mechanisms for Evolution

   • Microevolution: changes in a allele frequency in a population
     • Mutations
       • randomly introduces new alleles into a population. passed on from a sex cell.
     • Gene Flow
       • mating between two populations that changes the allele frequency of the populations.
         • Beneficial because it allows for greater genetic diversity/raw material.
     • Non- Random Mating
       • mating among individuals on the basics of mate selection for a particular phenotype (appearance) or due to inbreeding.
         • herds of caribou, males compete for mates using their antlers. Prevents individuals with weak phenotypes from breading.
         • Drawback: higher chance for deformities and health problems, low fertility rates, die young. preferred phenotypes=sexual selection
           • Sexual selection: organisms goes to extreme lengths for a mate.

5. Genetic Drift

   • Change in frequencies of alleles due to random events in breeding populations.
     • Smaller populations are less likely for the parent gene to be reflected in future generations.
   • Founder Effect
     • a change in a gene pool that occurs when few individuals start a new population
       • ex. various plants/ animals colonized Hawaii/ Galapagos Islands.
   • Bottleneck Effect
     • changes in gene distribution that result from a rapid decrease in population size.
       • ex. typhoon in Micronesia, resulting in 30 survivors and 1 had vision deficiency causing 10% increase in that disease for future generations.

6. Natural Selection

   • Stabilizing Selection
     • favours intermediate phenotypes (appearance) and acts against extreme variants.
       • This process selects against the extreme phenotypes and instead favours the majority of the population that is well adapted to the environment. (ex. average bird bill length)
       • Shown on a graph as a modified bell curve that is narrower and taller than the norm.
   • Directional Selection
     • favours the phenotypes at one extreme over another.
       • Resulting in distribution curve of phenotypes shifting in the direction of that extreme
       • ex. Bird Bills become longer since only deep flowers remain/ at an advantage. ex. increase in antibiotic resistance in infection causing bacteria.
   • Disruptive selection
     • favours the extremes of range of phenotypes rather than intermediate phenotypes.
       • Can result in elimination of intermediate phenotypes.
       • Can be caused by an event.
       • ex. average flower size whipped out, resulting in only long bills.

7. Artificial Selection

   • Carried out by humans on animals and plants to select traits of use to us.
     • Meat: cows- breed for meat/milk, pigs- size, chicken- grow faster for more consumption Plants: Bananas- collection of sweet/thiner peel seeds, vegetables from a plant- apples from a tree.
     • Benefits: greater amounts, larger animals (more meat),
     • Drawbacks: harvest to much causing a shortage, run out of the trait.

8. Speciation- Creation of New Species

   • Sympatric Speciation
     • creation of a new species within a population due to mutation.
       • Common in plants.
       • ex. apple maggot flies that all of a sudden fed on hawthorn apples (development of a new allele that caused the eventual creation of a new species.
   • Allopatric Speciation
     • creation of a new species due to geographic isolation.
       • Both populations adapt to their unique environments
         • Gene pools of both become distinct.
       • ex. salmanders in California.
   • Similarities
     • creation of new species
     • gene pools become separated over-time.

9. Evolutionary Pathways

   • Convergent Evolution
     • species with different ancestors become more similar in appearance due to similar environment.
       • “coming together”
       • ex. Mako shark and Tuna have similar body shapes.
   • Divergent Evolution
     • species with a common ancestor become more different over-time due to different environment pressures.
       • ex. North & South platypus in Australia (small and large).
     • “moving away”
   • Similarities
     • both pathways are shaped by the environment.
   • Coevolution
     • 2 species influence each other during evolution.
       • Benefit eachother
       • ex. Insect involves parts to feed on a specific flower, where the flower involves to get the pollen from that insect.

10. Reproductive Isolating Mechanisms

    • Post Zygotic Isolating Mechanisms
      • Mating has occurred.
        • Fertilized egg is formed
      • Prevention of Hybrids
        • Hybrid Breakdown
          • Losing the ability to have offspring overtime
        • Hybrid Sterility
          • Can't have babies
        • Hybrid Inviablility
          • Miscarrage
    • Pre- Zygotic Isolating Mechanisms
      • Preventing the sperm and egg from meeting
      • Prevention of mating
        • Behavioural Isolation
          • Different species have different behaviours to attract mates.
            • Ex. songs, dances
        • Temporal Isloation
          • Species mate at different times of the year
        • Habitat Isolation
          • Species live in different areas.
      • Prevention of fertilization
        • Prevent zygote from forming
        • Mechanical Isolation
          • genitalia are incompatilbe
        • Gametic Isolation
          • Sperm of another species cannot fertilize the eggs of another species.
    • Zygote: fertilized egg