Understanding Evolution: Evidence, Theories, and Mechanisms

Posted on Mar 1, 2025 in Biology

Evolution is the process that explains the diversity of species. It is caused by changes transmitted to offspring. Evolution is a fact.

Evidence of Evolution

Palaeontology

Palaeontology is the study of fossils (remains of past organisms). Dating determines when a fossil or rock was formed or when a geological event occurred. Dating can be relative or absolute.

Methods of Dating

  • Position of strata (depth = oldest)
  • Radioactive isotopes

Biogeography

Each continent has its flora and fauna. The presence of some organisms can be explained by the colonization of their ancestors.

Anatomical Evidence

  • Vestigial organs (remnants of past structures)
  • Homologous structures (structures with a common origin but different functions)
  • Analogous structures (structures with the same function but different origins)

Embryological Evidence

Similarities between embryos.

Biochemical Evidence

Greater uniformity in the molecular components of living beings.

Evolutionary Theory

Evolutionary theory explains the diversity of life based on the change of species over time.

Lamarckism

  • Spontaneous generation is a common fact.
  • Organisms have an internal impulse towards perfection.
  • Organisms adapt their bodies to the environment.
  • Acquired characteristics are inherited.

Lamarck believed that species are perfected through the use and misuse of their bodies as they adapt to the environment.

Darwinism

Natural Selection

  • Species evolve.
  • Evolution is gradual and continuous.
  • Offspring resemble their parents because they are descendants of a common ancestor.
  • Natural selection occurs:
    • Populations exhibit high biological variability.
    • An excess of offspring is produced.
    • Only a small portion can survive and reproduce.
    • Those with the best combination of characteristics to deal with the environment survive and reproduce, transmitting these traits to their offspring.

Neo-Darwinism

This is the most widely accepted theory now.

  • Populations of organisms experience mutations.
  • There is genetic variability.
  • Some variations increase biological fitness.

A species can evolve due to a mutation, and through this mutation, the species becomes stronger, and natural selection is true.

Genetic Variability

Genetic variability refers to the differences between the biological characteristics of individuals of a species. This includes genetic (differences in genes) and phenotypic (observable differences) variations.

Sources of Genetic Variability

  • Parasexual phenomena (DNA exchange)
  • Sexual reproduction (meiosis)
  • Mutations

Mutations

Mutations are changes in the DNA sequence.

Causes of Mutations

  • Errors in the separation and distribution of DNA before meiosis.
  • Mutagenic agents.
  • Errors in DNA replication or the mechanisms of reproduction.

Types of Mutations

  • Gene mutations: affect a particular gene. Can be deletions (loss of a base), insertions (addition of a base), or substitutions.
  • Chromosomal mutations: affect chromosomes. Deletion, duplication, inversions, translocations (exchange of places). Aneuploidy (lack or excess of a chromosome: monosomy, trisomy). Polyploidy (more than one set of chromosomes).