Evolution Unit Summary

Concepts/Terms

• Natural Selection - process by which organisms that are best adapted for survival/reproduction pass on their genes to future generations while others don’t

  • In a pop, overproduction of offspring will create more competition. Those who can survive/reproduce are better suited for the environment and will eventually outcompete other organisms who aren’t as well adapted

  • Results in accumulation of adaptations that increase fitness

  • Fitness - ability of an organism to reproduce

  • Works on individuals selecting for phenotype

• Artificial Selection - human intervention in selecting desirable traits to be passed on

  • Eg. selecting for cows that produce more milk (choosing cows that produce more and breeding them together for more)

• Biogeography - patterns of where stuff lived → useful in showing where ancestors lived/when

• Structures

  • Homologous Structures - Two organisms/species that share traits b/c of a common ancestors

    • Eg. Dinosaurs and humans with arm bones

    • Common Ancestor -

  • Analogous Structures - Two organisms that share similar traits without a common ancestor

    • * No evolutionary relationship but similar function/form

    • Result of convergent evolution

      • CE - different organisms/structures being classified as similar despite being different

  • Vestigial Structures - Structures that once served a purpose but have progressively grown less prominent/important as the species evolves

    • Eg. Wisdom teeth - used to be useful in chewing but no longer serve a purpose

    • Typically become smaller or reduced (use it or lose it)

• Genetics

  • Sexual Selection - Organisms choosing mates based on phenotype or courtship displays

    • Eg. Blue footed boobie dances

  • Gene Pool - All available genes in a population

  • Allele Frequency - # of times a gene appears in the population

    • Codominant = 2 dominant alleles

  • Population Genetics - How a population changes genetically over time

  • Modern Synthesis - Current ideas on evolution/genetics that integrates ideas of multiple fields

• Evolution

  • Accumulation of adaptations that results in a more fit species. Occurs through reproduction on a population level → populations evolve, not individuals → individuals only select for individual traits (NS)

  • Micro vs Macro evolution

    • Micro: changes in allele frequency

    • Macro: creation of new species

• Mutation

  • Neutral Mutation - No impact

  • Point Mutation - Change in a base of the gene, can cause frame shift/insertion/deletion

  • Gene Duplication - Repeat of section of chromosome

• Types of Selection

  • Directional Selection

    • Shifts toward an extreme

  • Stabilizing Selection

    • Selection against extremes, favour intermediate area

  • Disruptive Selection

    • Shifts toward both extremes → can lead to speciation

• Genetic Drift

  • GD - Allele frequencies changing in a small population b/c of random chance

  • Bottleneck Effect - Mass extinction of large portion of population

    • Placing a cup over a few ants and killing the rest → only small amount of population survive

  • Found Effect - A few individuals start a new population in a new environment. May have diff AF than original population

    • Building a wall that separates part of a population and that group creating a new population

  • Gene Flow - Movement of genes in/out of a population (movement of fertile organisms)

    • Decrease diversity b/c with enough gene flow, everyone becomes more similar

  • Genetic Equilibrium - allele frequency does not change over time → Hardy Weinberg Principle

• Hardy Weinberg Principle

  • Allele frequencies of a population will be constant unless something causes a change

    • Inertia but in biology (stable unless acted on by something)

  • Calculated w/ p² + 2pq + q² = 1

    • P = dominant allele

    • Q = recessive allele

  • Conditions for HW

    • Random mating

    • Large population

    • No gene flow (immigration/emigration)

    • No mutations

    • No natural selection

• Speciation

  • Speciation - creation of a new species. Occurs when a group of a population becomes reproductively isolated. Usually happens after mass extinction events b/c of unoccupied niches

  • Biological species concept: Organisms that can reproduce w/ each other to produce fertile/viable offspring are a species

    • Excludes asexual reproductive organisms and fossils/extinct species

  • Two types

    • Allopatric Speciation - Formed when parent population becomes geographically isolated

      • Literal blockages (eg. geographic barriers)

    • Sympatric Speciation - Formed despite populations in same area

      • Vibe-based blockages (majority of pre-zyg barriers)

      • Reproductive isolation

      • Can also occur through polyploidy

        • Polyploidy - mutation resulting in extra set of chromosomes → typically seen in plants

          • Plants w/ 2+ sets of chromosomes from own species known as autopolyploid

  • Reproductive Isolation

    • Pre-zygotic Barriers - Before zygote → impede fertilization

      • Behavioral - Differences in how organisms attract mates (eg. bird song)

      • Geographic - Physical barriers (eg. mountains) (allopatric speciation)

      • Temporal - Differences in mating seasons (eg. at night vs morning)

      • Habitat - Live in different places, rarely encounter

      • Mechanical - “Parts don’t fit”

      • Gametic - Fertilization unable to occur, can be interior or exterior

        • Biochemical barriers - sperm can’t join to egg

        • Chem incompatibility - sperm just dies

    • Post-zygotic Barriers - Post formation of zygote → stuff gets weird

      • Embryo may spontaneously die

      • ↓ Hybrid viability - hybrid just dies

      • ↓ Hybrid fertility - hybrid is sterile

      • Hybrid Breakdown - progressively weaker offspring

  • If groups isolated for too long, may become too different → new species

• Other definitions of species

  • Morphological Species

    • Characterize based on structures

    • Very arbitrary

  • Ecological

    • Defines by niche/role in community

    • Also useless

  • Phylogenetic Species

    • Defines by shared genetic history

    • Difficult to distinguish b/c hard to determine how different something has to be to be considered a species

    • Sort of arbitrary but not as bad

• Punctuated Equilibrium - dry stretch then a ton of evolution then another dry stretch (heart beat monitor thing)

  • Idea to oppose gradualism (as proposed by Darwin)

People

• Charles Darwin - Proposed Theory of Evolution

  • Evolution happens b/c of natural selection

    • NS - process by which organisms that are best adapted for survival/reproduction pass on their genes to future generations while others don’t

• Jean-Baptiste Lamark - Proposed original idea for evolution (was very wrong)

  • “Idiot on evolution”

  • Thought organisms can dev/lose features through use and were acquired through parents (hereditary). Idea of perfecting through use

  • Scientists could change the traits of organisms through artificial selection and those traits could be passed down (this part was wrong)

• Thomas Malthus - Infinite growth but limited resources

  • Idea of scarcity limiting population growth

  • Offspring would need to compete for resources

• James Hutton + Charles Lyell - Proposed ideas of gradualism and Theory of Uniformitarianism/Law of Superposition

  • Lots of small changes over a long period of time make big changes. Same changes have been occurring throughout history

  • Old stuff on the bottom and new stuff goes on top of it

  • Challenged Georges Cuvier’s idea of catastrophism

• Miller-Urey

  • Recreated atmosphere of ancient earth to test how organic molecules might have formed

    • Created organic molecules (amino acids)

      • Amino acids synthesize proteins → carbs, lipids, etc