Introduction to Biology: Phylogenetic Trees, Domains, and the Scientific Method

Phylogenetic Trees and the Tree of Life

  • Phylogenetic Tree Definition and Function:

    • A phylogenetic tree is a graphical representation used by researchers and scientists to understand the origin of life, where organisms come from, and the common ancestors shared across life.

    • The Tree of Life consists of three main branches representing the primary domains of life.

  • Evolutionary Relationships within Domain Eukarya:

    • Examining a specific branch within the domain Eukarya illustrates evolutionary relationships among mammals such as the platypus, kangaroo, and human:

      • All mammals share a last common ancestor from which lineages evolved, diverged, and changed over time.

      • The last common ancestor between the kangaroo and the human existed along a distinct branch several thousand years ago, leading to the separation of the two species.

      • Humans share a more recent common ancestor and more common characteristics with kangaroos than with platypuses.

      • The last common ancestor shared by the platypus, kangaroo, and human lies much further back (deeper) on the evolutionary tree.

Taxonomic Hierarchy and Biological Domains

  • Taxonomy:

    • Taxonomy is the scientific system used for naming and classifying organisms.

    • There are 88 levels of taxonomic hierarchy.

    • Domain: The most inclusive level of taxonomy. Everything falls under a domain.

    • Species: The least inclusive level of taxonomy.

  • The Three Domains of Life:

    1. Domain Eukarya:

      • Composed of eukaryotic organisms (organisms whose cells contain a true nucleus).

      • "Eu" means true;