Evolution and Speciation: A Comprehensive Summary

Posted on Feb 19, 2025 in Biology

Theory of Natural Selection

Individuals within a population exhibit heritable variations. Organisms live longer than the environment can support, leading to competition. Some inherited variations give individuals survival advantages.

The Synthetic Theory (Neo-Darwinism)

This theory builds upon Darwinian ideas, incorporating new findings. Its core principles include:

  • The evolving unit is the population.
  • Environmental conditions favor the reproduction of well-adapted individuals.
  • Evolution is driven by gradual changes in genetic makeup.
  • Adaptation is any trait that enhances an organism’s survival and reproduction.
  • Biological efficiency refers to an individual’s genetic contribution to future generations.

Neutralism (Kimura)

Many DNA changes are neutral, with chance playing a significant role alongside natural selection in determining variations.

Theory of Punctuated Equilibria (Gould)

This theory challenges the gradual transition between organizational plans proposed by the synthetic theory, suggesting periods of rapid change interspersed with periods of stability.

Evolution and the Origin of Species

Speciation

Speciation is the process by which one species splits into two. This involves the separation of a population.

Allopatric or Geographic Speciation

A population is divided by a geographical barrier. A group migrates to a new location without other members of their species, establishing a new settlement (founder effect).

Sympatric Speciation

Speciation occurs without physical separation.

Polyploidy

Errors in meiosis can lead to diploid gametes and the origin of polyploid organisms.

Reproductive Isolation

Different populations of a species specialize in using specific habitats within the same geographic area.

General Model of Speciation

  1. Geographic Isolation: Two populations evolve independently.
  2. Accumulation of Genetic Differences: Increased divergence leads to genetic incompatibility, preventing fertile offspring between the populations.

Classification of Species

Taxonomy is the science of describing and classifying the diversity of nature.

Carl Linnaeus’s Classification

Linnaeus proposed organizing species into groups called taxa. Taxa with greater similarities are grouped into higher-level taxa, creating a hierarchy:

  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species

Classification of a Kind

  • Genealogy: Common ancestry.
  • Degree of Similarity: Cumulative evolutionary changes since divergence from a common ancestor.
  • Cladistics: Based solely on pedigree (common origin).
  • Phenetics (Numerical Taxonomy): Based on similarity.

Classification and Phylogeny

Evolutionary history can be represented by phylogenetic trees (phylogenies). These trees illustrate relationships between groups of organisms based on:

  • Anatomy
  • Fossil studies (data on the succession of organisms over time)