Introduction to Evolution (1)

Introduction to Evolution

Course: BIOL 1134: Evolution, Ecology and Diversity

Instructor: Paul Klawinski

Learning Goals

  • Understand the 5 forces of evolutionary change that shape populations over time.

  • Know the development of the Theory of Evolution via Natural Selection (TENS) as articulated by Darwin and Wallace, including the historical context and scientific debate surrounding these ideas.

  • Identify the 4 preconditions for evolution via natural selection, exploring their implications for population genetics and species adaptation.

  • Describe examples demonstrating that evolution has occurred or is currently occurring, using both contemporary observations and historical data to illustrate key concepts.

What is Evolution?

Biological Evolution: Refers to the changes in allele frequencies within a population over successive generations as organisms adapt to their environments.

Key Aspects:

  • Involves changes in allele or genotype frequencies over time, impacting population structure and dynamics.

  • Does not occur within individuals or communities/ecosystems, but at the level of populations, leading to speciation events.

  • Although evolution is often perceived as linear or directional, it can be random and influenced by stochastic events.

What are the 5 Forces of Evolutionary Change?

  1. Selection:

    • Natural Selection: Differential survival and reproduction of individuals due to inherited traits, driven by environmental pressures.

    • Sexual Selection: A form of natural selection where certain traits enhance mating success, impacting the gene pool.

  2. Mutation:

    • Random changes in DNA sequences, serving as the primary source of genetic variability.

    • Possible effects include no effects, minor effects, or significant effects on phenotype and fitness, which can alter the evolutionary trajectory of populations.

  3. Random Genetic Drift:

    • Random changes in allele frequencies can lead to significant evolutionary effects, especially in small populations due to chance events (e.g., natural disasters, loss of individuals).

    • Population Bottlenecks: A dramatic reduction in population size can result in loss of genetic diversity and increased impact of random genetic drift.

  4. Migration:

    • Also known as gene flow, migration can introduce new alleles into a population, influencing its genetic makeup and adaptability.

    • Founder Effect: Occurs when a few individuals colonize a new area, potentially leading to reduced genetic diversity in the new population due to limited gene pools.

  5. Non-random (Assortative) Mating:

    • Mating preferences can be based on genotype or phenotype, altering genotype frequency within a population but not necessarily allele frequency.

    • This can lead to increased genetic similarities within mate pairings across succeeding generations.

Discovery of the Theory of Evolution via Natural Selection

Key Figures:

  • Charles Darwin and Alfred Wallace: Both naturalists contributed to the foundation of evolutionary biology through their observations and the publication of their theories.

The Prevailing View in the Early 19th Century:

  • Beliefs included that the Earth was young (based on religious texts) and that species were immutable, with created forms remaining unchanged over time.

  • James Ussher's chronology (4004 B.C.E.) represented the extreme belief in a young Earth.

  • Recognition of extinction (e.g., by George Cuvier) challenged the notion of immutable species, setting the stage for evolutionary thought.

Influences on Darwin and Wallace

  • Malthus: His theory on population growth and competition highlighted struggles for survival that shaped Darwin’s and Wallace’s views on natural selection.

  • Paley: His argument for design in nature suggested a creator, but also posed questions about the mechanisms of change.

  • Humboldt and Lyell: Their geological insights influenced the understanding of deep time and the shared ancestry pivotal to evolutionary biology.

Darwin's and Wallace's Observations

  • Noticed significant similarities and differences among species across geographical regions, leading to the hypothesis of common descent and adaptive radiation.

Writing and Publication

  • Darwin confronted pressure to publish following Wallace's similar manuscript submission, culminating in the 1859 release of On the Origin of Species, which articulated the principles of natural selection and diversity in species.

Preconditions for Evolution via Natural Selection

  1. More Offspring than Can Survive: Produces competition for resources, resulting in a struggle for existence.

  2. Interindividual Variability: The presence of genetic variation among individuals provides the raw material for selection.

  3. Heritable Variation: Traits that can be passed to offspring are crucial for the continuation of advantageous variations.

  4. Variation Affects Reproductive or Survival Success: Those variations that enhance survival or reproduction become more common in future generations, shaping the population.

Evidence of Evolution

  • Fossil Record: Provides evidence of intermediate forms and transitions, showcasing the gradual change across species over geological time.

  • Homology: Examines anatomical structures across different species that share a common evolutionary origin, such as vertebrate limb structures, reflecting evolutionary kinship.

  • Molecular Evidence: Comparative genomic analyses reveal similarities among diverse organisms, supporting the concept of shared ancestry.

  • Real-time Observations: Ongoing evolutionary changes can be observed in species such as Darwin's finches, which exhibit adaptations to environmental changes, and the phenotypic evolution of crops, like variations in corn oil content in response to selective breeding practices.