Introduction to Classification

I. Classification

• Taxonomy: System of classifying organisms based on similarities and differences.

II. History

• Aristotle: Introduced the idea of placing animals in a hierarchical order.
• Carolus Linnaeus: Known as the father of modern taxonomy, a Swedish scientist.
  • Introduced the "Systema Naturae".
  • Developed binomial nomenclature (two-part naming system).
• Charles Darwin: Proposed the concept of natural selection.

III. Levels of Classification (7 groups - Taxa)

1. Domain
2. Kingdom
3. Phylum
4. Class
5. Order
6. Family
7. Genus
8. Species

IV. 5 Kingdom System

• Monera: Includes bacteria and all prokaryotic organisms.
• Protista: Single-celled eukaryotes.
• Plantae: Plant kingdom.
• Fungi: Kingdom of multicellular eukaryotes including molds, yeast, etc.
• Animalia: Animal kingdom.

V. How to Write Scientific Names

• Example: Rana clamitans (italicized when typing, underlined on paper).
• Abbreviated: R. clamitans (after full name is mentioned).
• Other forms: Rana sp., Rana spp.

VI. Importance of Scientific Names

• Latin is a non-evolving language, ensuring stability in names.
• They are universally recognized.

VII. Modern Taxonomy

• Phylogenetic Systematics: Classifying based on evolutionary relationships.
  • Goal: Reconstruct phylogeny or evolutionary tree.
  • Based on common descent, as proposed by Darwin.
  • Modern evidence (e.g., molecular techniques) sometimes contradicts traditional taxonomy, leading to revisions.
  • Domains introduced:
    1. Bacteria
    2. Archaea
    3. Eukarya
  • Elimination of Kingdoms:
    • Monera split into Archaea and Bacteria.
    • Protista divided into several new groups under Eukarya.
  • Kingdoms Animalia, Plantae, and Fungi remain.

Phylogenetic Systematics Characteristics

• Uses homologous traits to construct phylogenetic trees.
  • Ancestral (primitive) traits: Present in a common ancestor.
  • Derived (novel) traits: New traits that arise within a group.
  • Clade: Group sharing derived traits.
  • Branches indicate new taxonomic divergence.
  • Monophyletic taxa reflect true evolutionary history.

Types of Taxa

• Monophyletic: Includes all descendants of a common ancestor.
• Polyphyletic: Includes members from multiple ancestral forms (e.g., Kingdom Plantae).
• Paraphyletic: Excludes some descendants of a common ancestor (e.g., Class Reptilia excluding Class Aves).

Types of Characters Used in Phylogenetics

• Morphology: Shape, structure, and development.
• Biochemistry: DNA, proteins.
• Cytology: Chromosomal structure and function.