Geologic-Time-Scale

Natural Selection

  • Key Mechanism of Evolution: Independently developed by Charles Darwin and Alfred Russel Wallace.

  • Principles: Based on variation, inheritance, and differential survival; individuals with favorable traits are more likely to survive and reproduce.

  • Genetic Basis: Traits must have a genetic basis to drive long-term evolutionary change.

  • Examples: Darwin’s study of finches in the Galápagos, demonstrating adaptation to environmental conditions.

Mutation

  • Definition: A change in DNA sequence, providing new alleles and driving genetic variation.

  • Outcomes: Can be harmful (reduces fitness), beneficial (enhances fitness), or neutral (no effect).

  • Importance: Critical for evolution but spreads gradually and depends on their effect on survival and reproduction.

Genetic Drift

  • Definition: Random changes in allele frequencies, particularly impactful in small populations.

  • Types:

    • Bottleneck Effect: Drastic population reduction decreases genetic diversity.

    • Founder Effect: A small group forming a new population reflects limited genetic variability.

  • Opposition to Natural Selection: Can counteract natural selection, especially in small populations.

Gene Flow

  • Definition: The movement of alleles between populations through migration or gamete transfer.

  • Effects:

    • Increases Genetic Variation: Reduces differences among populations.

    • Promotes Adaptability: Prevents isolation and ensures evolutionary potential.

Recombination

  • Definition: The exchange of genetic material during meiosis, generating unique combinations in offspring.

  • Importance: Enhances genetic diversity by shuffling existing genes, complementing mutation as a source of variation.

  • Significance: Essential for populations to adapt to changing environments.