Evolution: A Comprehensive Overview

Posted on Oct 27, 2024 in Biology

Fixism (19th Century)

  • Species are immutable, remaining unchanged over time.
  • Current species are unchanged descendants of those that first appeared on Earth.
  • No species evolves.
  • Fossils belong to extinct species due to natural disasters. Present species are descendants of those that survived.

Creationism (20th Century)

  • Earth is approximately 6,000 years old.
  • Species were created by God and have remained unchanged.

Evolutionism

  • Creatures have evolved throughout Earth’s history, becoming increasingly differentiated.
  • Past flora and fauna were less evolved than present life, exhibiting lower diversity.

Lamarckism (Theory of Acquired Characteristics)

  • Environmental conditions change over time.
  • These changes create new needs, requiring individuals to adapt their habits and behaviors.
  • These new habits lead to physical changes (“the function creates the organ”).
  • Environmentally induced changes are transmitted to offspring, eventually changing the species.

Darwinian Evolution

  • Variability in Offspring: Small differences or variations within a species are heritable.
  • Struggle for Survival: Organisms tend to reproduce maximally, but limited resources lead to competition.
  • Natural Selection: Individuals with favorable variations survive, reproduce, and have more offspring.

Neo-Darwinism (Synthetic Theory of Evolution)

  • Rejects Lamarckism’s acquired characteristics.
  • Dismissed the idea of inheritance as a blending of parental traits.
  • Proposed the synthetic theory of evolution.

Synthetic Theory

  • The evolutionary unit is the population, not the individual.
  • Individuals within a population carry different alleles originating from mutations.
  • Certain alleles increase the likelihood of producing offspring, leading to stronger and more frequent phenotypes.
  • Natural selection is the “engine of evolution.”
  • New heritable characters arise through mutations or new gene combinations.
  • Beneficial characters increase survival and reproduction rates.
  • Detrimental characters decrease survival and reproduction rates.

Types of Developments

  • Variational Evolution: Gradual and progressive accumulation over generations.
  • Saltational Evolution: Sudden change creating a new species in a few generations.
  • Speciational Evolution: Alternating periods of stability and change, less sudden than saltational evolution.

Evidence of Evolution

  • Paleontological: Fossils reveal simpler life forms and extinct species.
  • Biogeographical: Species in isolated regions differ more.
  • Anatomical: Homologous structures have the same origin but may have different functions. Analogous structures have different origins but similar functions. Vestigial organs are atrophied remnants of ancestral structures.
  • Embryological/Cellular: Embryos of different species share similarities due to common ancestry.
  • Biochemical: All living things share the same organic molecules, indicating a common origin.

Speciation

  • Isolation: A population becomes isolated by a barrier, preventing interbreeding.
  • Differentiation: The isolated population develops random variations through mutations.
  • Divergence: Different environmental conditions and natural selection lead to increasing variation between populations.
  • New Species: Over time, isolated populations may lose the ability to interbreed, forming distinct species.