common names Fig 18.2

polynomial nomenclature

binomial nomenclature  Genus (genera) and species = scientific name Fig 18.1

hierarchical classification (Fig 18.3)

taxon (taxa)

only species exist in nature as biologically cohesive units

John Ray defined biological species concept Fig. 18.4

Phylogeny leads to classification (Image)

Systematics - The goal of systematics is to have classification reflect the evolutionary relationships of species.

Phylogenetic systematics (Cladistics)

Cladistics classifies organisms according to the order in time that branches arise along a phylogenetic tree, without considering the degree of divergence (how much difference).

- cladogram (Fig 18.5)

- ancestral characters

- derived characters

A phylogenetic tree must be

- A monophyletic taxon = a clade (Image)

- NOT a  polyphyletic taxon

Morphological characters used in determining the phylogeny of a group:

   - Analogous structures result from convergent evolution (Image)

   - Analogy vs. homology (Image)

   - Homologous structures evolve from the same ancestral structure though the function may differ.

Other characters can be used: ecology, physiology, molecular. Fig 18.7.

Traditional taxonomy weights some characters more than others. Fig 18.6


A phylogenetic tree should have an outgroup that is a closely related taxon recently ancestral to the organisms for which the phylogeny is being constructed. Ingroups share derived characteristics that the outgroup does not have. To determine characters to use, must determine if it is analogous or homologous. If homologous, must then decide if character is ancestral or derived.  Movie

Fig 18.8 - several systems of classification

Classification schemes - the Movie!

Domain Archaea  contains Kingdom Archaea



                  Non-extreme Archaea

Domain Bacteria contains Kingdom Bacteria

Domain Eukarya contains 3 valid kingdoms plus one kingdom of convenience

A tree of life.  Fig. 18.9.

Relationships between the kingdoms. Fig 18.10

Relationships between the domains. Image

Characteristics of the kingdoms. Table 18.1

Visit the Tree of Life to view the systematics of all living organisms.

Berkeley's Introduction to Systematics.

Berkeley's Introduction to Cladistics.