Introduction to Evolution

Intro to Evolution

  • Evolution: Biological change in heritable characteristics of populations over successive generations, indicating universal common descent for all life.

Supporting Evidence

  • Evidence comes from various scientific disciplines:

    • Paleontology: Fossils show past life forms and transitional stages.

    • Microbiology/Physiology: Universal genetic code (DNA/RNA) and shared cellular structures suggest common origin.

    • Anatomy: Homologous and vestigial structures point to shared ancestry and evolutionary change.

    • Embryology: Similarities in early embryonic development across species.

    • Biogeography: Geographical distribution of species aligns with evolutionary history.

Evolution Mechanisms

  1. Natural Selection: Individuals with advantageous traits survive, reproduce, and pass them on, increasing beneficial alleles.

  2. Mutation: Random DNA changes are the source of new genetic variation.

  3. Gene Flow: Movement of alleles between populations via migration, impacting genetic variation and similarity.

  4. Genetic Drift: Random fluctuations in allele frequencies, significant in small populations, leading to chance loss or fixation of alleles.

Key Concepts

  • Descent with Modification: Darwin's term for species accumulating differences from ancestors through adaptation.

  • Variation: Genetic differences within a species, crucial for natural selection.

  • Survival of the Fittest: Individuals best adapted to their environment are more likely to survive and reproduce.

  • Competition: Struggle for limited resources, driving natural selection.

  • Adaptation: Heritable traits enhancing survival and reproduction, resulting from natural selection.

Key Figures in Evolution

  • Charles Darwin: Proposed the theory of evolution by natural selection in "On the Origin of Species."

  • Alfred Russel Wallace: Independently conceived the theory of natural selection.

Critical Elements of Natural Selection

  • Natural selection requires:

    1. Variability: Heritable differences among individuals.

    2. Competition: For limited resources due to overproduction of offspring.

    3. Differential survival and reproduction: Based on advantageous traits.

    4. Adaptation: Accumulation of advantageous traits over time.

Effects of Genetic Drift

  • Bottleneck Effect: Population size dramatically reduced, altering allele frequencies and reducing genetic diversity.

  • Founder Effect: A small group establishes a new population, with a gene pool not representative of the original, due to chance.