Introduction to Evolution

Introduction

  • Course Title: BIOL 1134: Evolution, Ecology, and Diversity

  • Instructor: Paul Klawinski

Learning Goals

  • Understand the 5 forces of evolutionary change

  • Summarize how Darwin and Wallace developed the Theory of Evolution via Natural Selection (TENS)

  • Identify the 4 preconditions necessary for natural selection

  • Provide examples illustrating that evolution has occurred or is currently occurring

What is Evolution?

  • Definition:

    • Biological evolution refers to the change in allele frequencies within a population across generations.

    • It also encompasses the change in allele or genotype frequencies over time.

  • Key Notes:

    • Evolution does not occur within individuals.

    • It does not occur in larger ecological units like communities or ecosystems.

    • Evolution is not necessarily a directional process.

The 5 Forces of Evolutionary Change

  • Selection:

    • Natural selection

    • Sexual selection

  • Mutation: Random changes in DNA

  • Random Genetic Drift: Changes due to chance

  • Migration: Gene flow from one population to another

  • Non-random (assortative) mating: Preference in mating

  • Considerations:

    • Identify which forces increase vs. decrease genetic diversity.

Selection Factors

  • Changes in allele frequency due to survival and reproduction influenced by:

    • Abiotic factors (e.g., temperature, drought, floods)

    • Biotic factors (e.g., food availability, competition, predation)

  • Types of competition within species:

    • Male competition (Male: Male Competition)

    • Female choice in mate selection (Female Choice)

Mutation

  • Definition: Random alterations in the DNA sequence.

  • Occurrence:

    • Can happen anywhere within the nuclear, mitochondrial, or chloroplast genomes.

  • Effects of mutations:

    • May have no effect, minor effects, or major effects depending on location in the genome.

Random Genetic Drift

  • Definition: Random changes in allele frequency primarily due to chance events leading to death.

  • More pronounced in smaller populations.

  • Special cases include population bottlenecks.

  • Examples: Illustrative cast of characters to represent allele frequency changes in scenarios.

Migration and Founder Effect

  • Migration entails the movement of alleles from one population to another.

  • Founder Effect: Occurs when a small group establishes a new population, leading to reduced genetic diversity.

Non-Random (Assortative) Mating

  • Definition: Individuals preferentially mate based on genetic or phenotypic similarity or dissimilarity.

  • Outcomes:

    • Changes genotype frequency without necessarily affecting allele frequency.

Discovery of the Theory of Evolution via Natural Selection

  • Key Figures:

    • Charles Darwin (1809) and Alfred Russel Wallace (1823)

  • Evolutionary thought in the 19th century:

    • Previous beliefs included the idea of species being immutable and the Earth being static.

    • George Cuvier’s evidence of extinction, James Hutton and Charles Lyell’s concepts of gradual geological processes.

    • Influence of Jean-Baptiste Lamarck’s theories of acquired characteristics.

Lamarck's Theory of Evolution

  • Hypothesized that acquired traits were inherited (e.g., giraffe ancestor stretching to reach leaves).

Influences on Darwin and Wallace

  • Thomas Robert Malthus: Wrote about population pressures.

  • William Paley: Introduced the watchmaker analogy suggesting a divine creator.

  • Alexander von Humboldt: Explored ecological and geological systems.

  • Darwin’s voyage (1831-1836) was instrumental for his observations.

Observations of Evolution by Both Scientists

  • Darwin observed variations in species particularly tortoises in the Galápagos Islands.

  • Wallace noted geographical isolations in species, e.g., Amazonian monkeys.

Writing and Publication Process

  • Darwin struggled to publish but eventually provided his thesis on species origins.

  • In 1858, Wallace’s manuscript prompted Darwin to publish his findings.

Preconditions for Natural Selection

  1. Excess Offspring: More offspring are produced than can survive, leading to competition.

  2. Phenotypic Variation: There is variation among individuals within a population.

  3. Heritability: Variations are heritable, allowing traits to pass on to the next generation.

  4. Differential Success: Individuals with certain traits have variations in reproductive success or survival.

Evidence for Evolution

  • Fossil Record: Should display intermediate forms indicating evolutionary pathways.

  • Homology: Similar structures among different species show common ancestry.

  • Molecular Evidence: Genomic similarities reflect shared evolutionary paths.

  • Real-time Evolution Observations: Examples include changes in Darwin's finches during environmental shifts and modern agricultural traits in corn.