Understanding Biological Evolution and Speciation

Posted on Mar 3, 2025 in Fine Arts

Evolution: Key Concepts and Mechanisms

Evolution is defined as a change in a population over time, resulting in new organisms or extinction.

Homologous structures are similar structures in two organisms that indicate a common ancestor.

Jean-Baptiste Lamarck’s Hypothesis

  • Organisms strive to improve themselves.
  • Inheritance of Acquired Characteristics: He believed that traits acquired during an organism’s lifetime could be passed on to its offspring. For example, he thought children of blacksmiths naturally inherited muscles.
  • Use and Disuse: Body parts that were used were developed, and those that were not used wasted away.

Lamarck’s hypotheses were disproven by August Weismann, who demonstrated that offspring did not inherit acquired traits (e.g., mice whose tails were cut off did not produce tailless offspring).

Charles Darwin and Natural Selection

  • Darwin traveled on the H.M.S. Beagle to the Galapagos Islands, where he made crucial observations.
  • He noted that finches on different islands had different beak sizes, adapted to their specific food sources.
  • Points of Natural Selection:
    1. Populations have variations (resulting from recombination, mutation, and sexual reproduction).
    2. Some variations are favorable.
    3. More offspring are produced than survive.
    4. Those that survive possess the favorable trait.
    5. Over time, the population will change, and all individuals will have the favorable trait.

Natural Selection & Evolution: Natural selection causes evolution. When the environment changes, some organisms are better adapted than others, leading to their survival (natural selection) and the evolution of the population towards the more adapted state.

Antibiotic resistance exemplifies natural selection, as bacteria resistant to antibiotics survive and reproduce rapidly.

Selection Graphs

  • Stabilizing Selection:

    fH-RXmKQXwmr-OWLL2VS1adxnB6tL3PcNCpeRyOw

    The intermediate phenotype is favored, while extremes are selected against.

  • Directional Selection:

    42gNQpcHl8eglAagSOFSO3YTBYYlYIZnRACINQCI

    One extreme phenotype is favored, while the other extreme is selected against.

  • Disruptive Selection:

    4hE5-ASfXALPV30bpR_fdpwBjKCGHpDIr-kqwOe5

    Extreme phenotypes are favored, while the intermediate phenotype is selected against.

Genetic Equilibrium

A population reaches genetic equilibrium when it becomes stable. Four (five) conditions are necessary for this:

  1. Random mating
  2. Large population size
  3. No mutations
  4. No immigration or emigration
  5. Speciation

Speciation

  • Species: A group of organisms that can interbreed and produce viable, fertile offspring.
  • Reproductive Isolation: Mechanisms that prevent interbreeding between different species.
    • Behavioral Isolation: Populations cannot reproduce due to differing mating rituals.
    • Geographical Isolation: Populations are physically separated and cannot reproduce.
    • Temporal Isolation: Populations have different reproduction times, preventing interbreeding.

Patterns of Evolution

  1. Extinction: All members of a species die, and it can no longer reproduce (caused by natural selection).
  2. Adaptive Radiation: One ancestral species evolves into many diverse forms.
  3. Convergent Evolution: Organisms with different ancestors develop similar traits due to similar environmental pressures.
  4. Coevolution: Closely connected organisms evolve together.
  5. Gradualism: Organisms change gradually and steadily over time.
  6. Punctuated Equilibrium: Rapid, random changes occur in a species over a short period.

(No natural selection in Punctuated equilibrium)