Lecture 14: Evolution I – The Theory

Introduction

  • Course: Biol 103: Introductory Biology I Lecture 14 Evolution I – The Theory
  • Instructor: Dr. Michael D. Preston, Assistant Professor, Ecosystem Science and Management
  • Contact: michael.preston@unbc.ca
  • Office Hours: 12:20 pm - 1:00 pm Mon/Wed/Fri or by appointment

Learning Objectives

  • Outline the developments that led to the theory of evolution.
  • Explain how natural selection causes evolution of organisms.
  • Describe examples of evolution.
  • Readings: Chapter 16 – Evolution: The Development of a Theory.
  • Note: There is no associated quiz.

Seeds of the Theory

  • Famous quotation by Theodosius Dobzhansky: "Nothing in biology makes sense except in the light of evolution."

What is Evolution?

  • Definition: Evolution refers to the slow change of species over time.
  • Example Species Timeline:
    • Present Day: Chimpanzee.
    • Millions of Years Ago:
    • 3 species of Hominins:
      • Paranthropus boisei.
      • Paranthropus robustus.
      • Paranthropus aethiopicus.
    • Modern species include:
      • Homo sapiens.
      • Homo neanderthalensis.
      • Homo erectus.
      • Australopithecus garhi.
      • Multiple species of Homo, possibly up to 21.

Evolutionary Pathways

  • Broad range of species includes mammals, birds, reptiles, and various invertebrates.
  • Illustration of the evolutionary tree showcasing various taxa and their origins.
    • Examples: Spiders, Crabs & Lobsters, Insects, Jellyfish & Sea Anemones, Protozoa, Sponges.

Evolution by Natural Selection

  • Natural selection is a key mechanism of evolution.

Antibiotic Resistance

  • Definition: Antibiotic resistance in bacteria is a consequence of evolution by natural selection.
  • Visual representation demonstrating shifts in microbial resistance before and during drug treatment.
    • Initial low resistance observed in microbial populations before treatment.
    • Following treatment, immune responses can lead to no detectable microbes, showcasing immunity synergy and microbial rebounds.

Natural Selection and Drug Resistance Dynamics

  • Example Data Diagram:
    • Resistance levels shift from low to high post-drug treatment.
    • Possible outcomes include:
    • Immune clearance leading to temporary resolution.
    • No immune clearance resulting in rebounds of microbial populations.
    • Further genetic changes prompt higher resistance.
    • Premature drug termination contributing to resistance development.

Selection for Desired Traits: Artificial Selection

  • Definition: Artificial selection occurs when humans act as the selective agents.
  • Example: Teosinte was selectively bred into corn (maize).
  • Variants of Brassica oleracea were developed through selective breeding leading to:
    • Broccoli (flower bud selection).
    • Cauliflower (floral selection).
    • Kale (leaf selection).
    • Cabbage (root selection).
  • Visual reference of evolution from wild mustard to various vegetables.

Fitness in Natural Selection

  • Definition: Fitness refers to the reproductive success of organisms.
    • Organisms with heritable traits that allow survival against limited resources or predation will produce more offspring.
    • Formula: Fitness = Reproductive Success

Natural Selection Among Variants

  • Clarification:
    • Individuals do not evolve; populations do.
  • Example of the Woolly Mammoth:
    • Environmental adaptation does not occur at the individual level.

Populations Change Over Time

  • Illustration:
    • Generation 1 goes through selection, leads to Generation 2, and continues to Generation 3 through repeated selection stages.

Defining Evolution

  • Evolution is measured by changes in allele frequency within populations over time.
  • Key concept: Favorable traits enhance survival and reproduction in certain environments.

Natural Selection Impacts

  • Definition: Selection pressure is the external factor influencing survival within natural populations.
  • Examples of selection pressures include:
    • Resource limitations: food and habitat.
    • Predators and competition.

Evidence for Evolution by Natural Selection

  • Early evidence stems from isolated island populations, exhibiting unique adaptations reflecting selective pressures.
    • The Galápagos Islands serve as a prime study site.
    • Mockingbird species (genus Nesomimus) derived from a common ancestor adapting to different environmental conditions (e.g., beak size, color).

Descent with Modification

  • The concept suggesting all organisms are related through descent from a common ancestor.
  • Adaptations arise due to differing pressures leading organisms to evolve favorable traits.

Fitness Revisited

  • Definition: An individual’s reproductive success is greater if they leave more surviving offspring.
  • Key Aspects of Fitness:
    1. Fitness is relative.
    2. Traits must improve fitness to be deemed adaptive.
    3. Adaptive traits can change over time.

Source of Variation: Random Mutation

  • Variability arises from mutations, which are random, heritable changes in DNA, contributing to diverse traits in populations.
  • Influences include errors during DNA replication and environmental factors.

Natural Selection is NOT Random

  • Explanation: Mutations do not intentionally produce advantageous traits.
  • Natural selection acts upon these random changes effectively and strategically, impacting survival.

Examples of Natural Selection

  • Peppered Moth (Biston betularia): Environmental changes alter natural selection outcomes.
  • Monarch Butterfly: Adaptation to milkweed via genetic mutation grants immunity.
  • Bark Scorpion: Grasshopper Mouse illustrates evolved analgesic capacity as a pain response adaptation.

Experimental Evolution and Generation Time

  • Overview: Varied species have different generation times influencing the rate of evolution, detailed through examples from plants to bacteria.
  • Relative fitness defined as Growth rate of evolved population divided by Growth rate of ancestral population.

Transitional Forms

  • Reference: Archaeopteryx and its significance in illustrating transitional forms in the fossil record demonstrating evolutionary changes.

Historical Development of Evolutionary Theory

  • Key Figures and Contributions:
    • Carolus Linnaeus: Classification system.
    • Jean Baptiste de Lamarck: Early theories suggesting species change.
    • Charles Darwin: Formalized the theory of evolution by natural selection following his voyage on HMS Beagle (1831-1836) and publication of The Origin of Species in 1859.

Influential Ideas in Evolutionary Theory

  • Geology: Work of Cuvier, Hutton, and Lyell laid foundational understanding of gradual changes in life's history relating to evolutionary principles.
    • Examples: Fossils atop mountains and similarities among deposited species.

Biogeography

  • The study of geographic distribution of species and factors affecting distributions, including environmental adaptations.
    • Observations regarding similarity among species across islands and varying conditions promoting adaptation.

Morphology and Structural Similarities

  • Homologous Structures: Similar underlying anatomy indicating a shared ancestry.
  • Vestigial Structures: Structures diminishing in function as seen in some species.

Limitations on Population Growth

  • Concept by Thomas Malthus on exponential growth of populations and potential resource constraints leading to survival challenges.

Observations, Hypotheses, and Predictions

  • Ernst Mayr’s summarized approach to Darwin’s key elements laid out in the On the Origin of Species, highlighting observations and their implications for evolutionary theory.

Four Characteristics of Darwin’s Theory

  1. Biological diversity origins explained by physical processes.
  2. Evolution occurs within groups (populations), not individuals.
  3. Multistage evolution happens over many generations.
  4. Some organisms are more efficient in survival depending on their environmental fit.

Principles of Natural Selection in Agricultural Contexts

  • Example: Pesticide resistance illustrating the pressures and resultant evolutionary adaptations in pest populations.

Common Misconceptions

  1. Evolution and natural selection are indistinguishable.
  2. Evolution is gradual; factors influencing rates (like generation time) create variability.
  3. Selection acts on individuals; population evolution is the actual outcome.
  4. Natural selection is directional, but it operates blindly based on existing variations.
  5. Traits arise in response to environmental changes; however, variability preexists, enabling adaptation.
  6. Selection influences phenotypes, while human evolution remains ongoing despite modern conditions.

Conclusion

  • Understanding the principles of evolution via natural selection is integral for grasping biological diversity and behavioral attributes among species.