BIO II

Evolution and Its Mechanisms

  • Definition of Evolution:

    • Mechanism for species changing over time.

    • Descent with modification.

  • Population Evolution:

    • Populations evolve as frequencies change; individuals do not evolve.

    • Variation within populations is determined by genes in the population's gene pool, altered by mutation.

  • Role of Natural Selection:

    • Explains organism adaptations and the unity/diversity of life.

    • Causes species to change and diverge over time, heavily influenced by reproductive success of individuals with favorable traits.

  • Mechanism of Natural Selection:

    • Beneficial genetic mutations are passed on through reproduction.

Principles of Natural Selection

  1. Heritable Characteristics: Must be passed from parents to offspring.

  2. Overproduction and Competition: More offspring are produced than can survive; this creates competition for resources.

  3. Genetic Variation: Offspring exhibit genetic differences which affect survival and reproduction. Changes occur in populations over generations.

Adaptation and Maladaptation

  • Adaptation:

    • A heritable trait increasing individual fitness, enabling better competition for limited resources.

    • Environmental conditions determine whether a trait is an adaptation.

  • Maladaptation:

    • A negative trait reducing fitness; traits can become maladaptive as environmental conditions change.

Theories of Evolution

  • Lamarckian Evolution:

    • Change occurs in organisms over time through:

      1. Use and Disuse: Parts used extensively grow; unused parts diminish (incorrect interpretation).

      2. Inheritance of Acquired Characteristics: Traits acquired during an organism's life are passed to offspring (incorrect interpretation).

  • Darwin and Wallace:

    • Adaptation of organisms to their environment and new species origins are linked processes.

    • Observations about adaptation in different environments leading to species variations.

Observations and Implications

  • Darwin's Observations:

    • Organisms are adapted to specific environments.

    • Different islands hold similar but distinct species related to mainland forms.

  • Wallace's Insights:

    • Identified similar adaptation patterns across species.

    • Proposed natural selection as an independent theory.

Mutation and Its Effects

  • Effects of Mutation on Phenotype:

    1. Neutral effect (no impact).

    2. Reduced fitness (less competitive).

    3. Increased fitness (more competitive).

Evolutionary Processes

  • Convergent Evolution:

    • Organisms without a recent common ancestor evolve similar traits due to similar environmental pressures.

    • Example: sharks and dolphins.

  • Divergent Evolution:

    • Organisms with a recent common ancestor evolve differently to adapt to diverse environments.

    • Example: evolution of horses from a common ancestry.

Evidence for Evolution

  • Fossil Records:

    • Solid evidence showing that past organisms differ from today's, demonstrating evolutionary progression.

  • Anatomy:

    • Study of body structures provides insights into evolutionary relationships.

  • Embryology:

    • Comparisons of developmental stages help illustrate relatedness.

  • Biogeography:

    • Examines the distribution of organisms across geographic areas.

  • Molecular Biology:

    • Focuses on macromolecules essential to life, revealing insights into evolutionary history.

Speciation

  • Species Definition:

    • A group of organisms capable of interbreeding and producing fertile offspring. Separation indicates distinct species.

  • Types of Speciation:

    1. Allopatric Speciation:

      • Geographic separation leads to new species evolution.

      • Types include dispersal and vicariance.

        • Dispersal Speciation: Members move to new areas.

        • Vicariance Speciation: Physical barriers arise.

    2. Sympatric Speciation:

      • Speciation occurs within a single location due to genetic differences, often due to resource competition.

Mechanisms of Speciation

  • Reproductive Isolation:

    • Prevents interbreeding between species, resulting in reduced viability or infertility in hybrids.

  • Prezygotic Barriers:

    • Mechanisms preventing mating or fertilization. Types include:

      • Temporal: Different breeding seasons.

      • Habitat: Same area, different habitats.

      • Behavioral: Different mating rituals.

      • Mechanical: Incompatible reproductive structures.

  • Postzygotic Barriers:

    • Zygote does not develop or hybrid offspring are sterile.

      • Types include zygotic inviability and hybrid infertility.

Hybrid Zones and Speciation Dynamics

  • Hybrid Zones:

    • Areas where interbreeding between diverging species occurs.

    • Outcomes include reinforcement, fusion, and stability of species.

  • Punctuated Equilibrium vs. Gradual Speciation:

    • Punctuated Equilibrium: Quick divergence followed by long stability.

    • Gradual Speciation: Slow, gradual evolutionary changes.

Genetic Concepts

  • Gene and Allele Definitions:

    • Gene: Unit of DNA coding for proteins.

    • Allele: Alternative forms of a gene.

  • Genotype and Phenotype:

    • Genotype: Genetic constitution; Phenotype: Observable traits influenced by genotype.

  • Microevolution and Macroevolution:

    • Microevolution: Small changes in a population's allele frequencies.

    • Macroevolution: Large changes extending over time leading to species formation.

Genetic Equilibrium

  • Hardy-Weinberg Equilibrium:

    • Conditions under which allele frequencies remain constant; non-evolving populations make predictions via formulas.

  • Assumptions for equilibrium:

    1. No gene flow.

    2. No natural selection.

    3. No mutation.

    4. Random mating.

    5. No genetic drift.

Natural Selection Types

  • Adaptive Evolution:

    • Increases frequency of beneficial traits while decreasing deleterious traits.

  • Relative Fitness:

    • Measure of an individual’s fitness compared to others.

  • Selection Types:

    1. Stabilizing Selection:

      • Selective pressure favors the average.

    2. Directional Selection:

      • Favors one extreme phenotype.

    3. Disruptive Selection:

      • Favors both extreme phenotypes.

    4. Frequency-Dependent Selection:

      • Fitness varies with phenotype prevalence.

Sexual Selection

  • Sexual Dimorphism:

    • Phenotypic differences between sexes due to selection.

  • Handicap Principle:

    • Extravagant traits serve as honest signals of fitness.

Taxonomy and Phylogeny

  • Taxonomic Groups:

    • Move from inclusivity to exclusivity to show relatedness.

  • Binomial Naming System:

    • Uses genus and species names for classification (e.g., Panthera pardus).

  • Phylogenetic Trees:

    • Show evolutionary relationships among species.

      • Clades: Groups from a common ancestor.

      • Monophyletic: Contains common ancestor and all descendants.

      • Polyphyletic: Includes unrelated species without a common ancestor.

      • Paraphyletic: Includes some, but not all, descendants.

Evolutionary Relationships

  • Homologous vs. Analogous Structures:

    • Homologous: Similar due to common ancestry.

    • Analogous: Similar traits not due to recent common ancestors; arise due to similar environmental pressures.

  • Synapomorphy, Plesiomorphy, Autapomorphy:

    • Shared derived traits among descendants, ancestral characters, and unique traits to a taxon, respectively.

  • Maximum Parsimony:

    • Phylogenetic tree with fewest evolutionary steps is the likely correct one.