Evolutionary Agents, Adaptation, and Biodiversity

Posted on Feb 19, 2025 in Biology

Evolutionary Agents

Evolutionary agents cause changes in gene frequencies within a population. These agents include:

  • Mutations: Changes in genetic information that introduce new alleles, leading to variability within the population. Mutations occur randomly, and the environment determines whether a mutation is neutral, harmful, or beneficial.
  • Genetic Drift: Random changes in allele frequencies from one generation to the next, particularly significant in small populations.
  • Gene Flow: The transfer of genes from one population to another through migration, spreading alleles across populations.
  • Natural Selection: The driving force of evolution, involving differential reproduction based on phenotypes. Natural selection acts on three types:
    • Stabilizing Selection: Favors individuals with intermediate phenotypes.
    • Directional Selection: Favors individuals with phenotypes at one extreme.
    • Disruptive Selection: Favors individuals with phenotypes at both extremes, away from the average.

Adaptation

Adaptation refers to any trait (anatomical, physiological, or behavioral) that allows an organism to thrive in its environment.

Speciation

Species: A group of individuals with morphological similarities capable of interbreeding to produce fertile offspring and reproductively isolated from other species.

Speciation: The process of forming a new species from an initial one (E1 -> E2). It is caused by genetic isolation, which interrupts gene exchange between distinct populations of the same species.

  • Geographic Isolation: Spatial separation between populations due to geographical barriers, preventing interbreeding. This leads to genetic divergence through mutations, natural selection, and adaptation. This mechanism is called allopatric speciation.
  • Reproductive Isolation: Populations occupy the same space but do not interbreed due to reproductive isolation mechanisms, such as:
    1. Differences in courtship behavior
    2. Changes in floral structures
    3. Becoming sexually mature at different times
    This mechanism is called sympatric speciation.

Biodiversity

Biodiversity is the variety of biological species. Approximately 1.75 million species have been identified to date. The origin of this diversity lies in evolution, driven by:

  1. Mutation
  2. Natural Selection
  3. Reproductive Isolation

These factors have shaped the tree of life, with new species arising from existing ones through evolution.

Classification of Organisms

Organisms are classified based on their similarities and evolutionary history. There are eight main taxonomic categories:

Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species. Species is the basic unit of classification and the unit of evolution.

Extinctions

Extinction is the disappearance of a species or group of species. Types of extinctions include:

  1. Background Extinction (continuous, low-level extinction)
  2. Mass Extinction (e.g., Permian extinction 250 million years ago, Cretaceous extinction 65 million years ago)

The Origin of Life

Theories on the origin of life propose that organic matter could originate from inorganic molecules on the primitive Earth, which had the following characteristics:

  1. Reductive and Anaerobic Atmosphere: Very little free O2, rich in water vapor, CO2, CH4, NH3, N2, etc., providing the primary bioelements (CHON).
  2. Abundant Energy: High-energy solar radiation (due to the absence of ozone), thermal energy, electrical storms, etc.
  3. Atmospheric gases reacted to form simple organic molecules, which accumulated in lakes and seas, creating a primitive soup or broth.
  4. Simple organic molecules reacted to form complex molecules like proteins and nucleic acids.
  5. These molecules were surrounded by a membrane, forming protobionts, which were the ancestors of cells.
  6. The Miller Experiment demonstrated the synthesis of organic compounds from inorganic components of the early Earth’s atmosphere.