lecture recording on 18 March 2025 at 09.12.49 AM

Taxonomy

• Taxonomy: The science of naming and classifying organisms, revealing their interrelationships.

• Historical Classification: Early systems were based on observable traits. The introduction of DNA analysis improved accuracy in classification.

Biological Classification Hierarchy

• Levels of Classification:

  • Species: The most specific category.

  • Genus: The group of related species.

  • Family: Groups of related genera (plural of genus).

  • Order: Composed of related families.

  • Phylum (Animal classification) / Division (Plant classification): Higher taxonomic levels than order.

• Example:

  • Human: Homo sapiens (species)

  • Genus: Homo

Evolution of Taxonomic Systems

• Five Kingdoms System:

  • Early classifications categorized life into five kingdoms:

    • Bacteria

    • Fungi

    • Plants

    • Animals

  • Recognized limitations due to prokaryotic organisms being too diverse within a single kingdom.

  • Shifted to three domains:

    • Domain Bacteria (prokaryotic bacteria)

    • Domain Eukarya (including animals, plants, fungi)

    • Domain Archaea (ancient, extremophile single-celled organisms).

Species Classification and Subspecies

• Species Definition: Group of organisms that can interbreed and produce fertile offspring.

• Subspecies: Divisions within a species; for example, humans and Neanderthals categorized as different subspecies (Homo sapiens sapiens vs. Homo sapiens neanderthalensis).

• DNA analysis helped confirm relationships and interbreeding possibilities, leading to the understanding that Neanderthals contributed to modern human DNA (especially among people of European descent).

Phylogeny and Phylogenetic Trees

• Phylogeny: The evolutionary history and relationships among species.

• Phylogenetic Trees: Visual representations of evolutionary relationships:

  • Show common ancestors and branching patterns indicating evolutionary divergences.

  • Can illustrate basal taxa referring to species that have changed little over time.

Understanding Phylogenetic Data

• Morphological and Molecular Data: Used to infer phylogenies.

  • Morphological data focuses on body structures.

  • Molecular data looks at genetic sequences, providing insight into homologies (similarities due to common ancestry) vs. analogies (similarities not due to common ancestry).

Types of Taxonomic Groups

• Monophyletic group: Includes an ancestor and all its descendants.

• Paraphyletic group: Includes an ancestor and some, but not all, of its descendants.

• Polyphyletic group: Groups that do not include the most recent common ancestor for some of their members.

Phylogenetic Attributes and Characters

• Examples of derived characters in a shared character table:

  • Outgroup: Closely related organisms that lack certain characteristics; provides a comparison basis for assessing traits in related groups.

  • Examples: Vertebral column as a shared ancestral character in chordates.

Evolutionary Traits and Characteristics

• Evolutionary Milestones:

  • Backbone in chordates (lampreys).

  • Development of hinged jaws (fish), followed by four limbs (amphibians), leading to the amniotic sac in reptiles.

  • Mammals characterized by body hair, highlighting evolutionary complexity.

Molecular Clocks and Evolutionary Timing

• Molecular clocks estimate timing of evolutionary events based on mutation rates in DNA, allowing predictions about divergence times among species.

• Understanding that the branches on phylogenetic trees can indicate relations without precise timing; its complexity means timing estimates can vary significantly.