OA

bsci 160 9/12/25 Evolution: History, Evidence, and Mechanisms

1. Overview of Evolution

  • Evolution is the change in heritable characteristics of biological populations over successive generations.

  • It provides a unifying framework for understanding the diversity of life on Earth.

2. Emergence of the Major Theory

  • Pre-Darwinian Ideas: Earlier concepts of change over time, but lacked a robust mechanism.

  • Lamarckism: Proposed inheritance of acquired characteristics, an incorrect mechanism.

  • Charles Darwin and Alfred Russel Wallace: Independently conceived the theory of natural selection as the primary mechanism for evolutionary change.

  • "On the Origin of Species" (1859): Darwin's seminal work detailing the theory of evolution by natural selection.

3. Key Players in Evolutionary Thought

  • Charles Darwin: Developed the theory of natural selection based on observations during his voyage on the HMS Beagle.

  • Alfred Russel Wallace: Independently arrived at similar conclusions about natural selection, prompting joint presentation of their ideas.

4. Evidence for Evolution

  • Fossil Record: Demonstrates transitional forms and changes in species over geological time.

  • Comparative Anatomy: Similarities in bone structures (homologous structures), like the pentadactyl limb across vertebrates, suggest common ancestry.

  • Embryology: Similar developmental patterns in embryos of different species indicate shared ancestry.

  • Molecular Biology & Genetics: Comparisons of DNA and protein sequences reveal evolutionary relationships and divergence times.

  • Biogeography: The geographical distribution of species reflects evolutionary history and adaptation to different environments.

  • Direct Observation: Examples include antibiotic resistance in bacteria (E. coli) and pesticide resistance in insects, showing evolution in action over short timescales.

5. Basic Mechanisms of Evolution (Beyond Natural Selection)

  • Natural Selection: Differential survival and reproduction of individuals due to differences in phenotype, leading to adaptation.

  • Genetic Drift: Random fluctuations in allele frequencies, particularly impactful in small populations.

    • Bottleneck Effect: A drastic reduction in population size leading to a non-representative sample of alleles.

    • Founder Effect: A new population established by a small number of individuals, leading to a different allele frequency from the parent population.

  • Gene Flow (Migration): The movement of alleles between populations, which can introduce new genetic variation or homogenize populations.

  • Mutation: Random changes in the DNA sequence; the ultimate source of new genetic variation.

  • Non-Random Mating: Occurs when individuals choose mates based on specific traits, altering genotype frequencies but not allele frequencies directly (e.g., assortative mating).

6. Classroom Logistics

  • Discussions on deadlines and grading policies for the course.

7. Philosophical and Practical Implications

  • Evolution as a Non-Goal Process: Evolution does not strive towards a "perfect" or predetermined outcome; it's a response to current environmental pressures.

  • Resistance to Evolutionary Ideas: Discusses societal and historical challenges in the acceptance of evolutionary theory.

  • Humans Not Occupying a Privileged Peak: Em