27.5 Systematics (Naming Organisms)
Learning goals:
1. Discuss how phylogenetics is used to classify organisms
2. Cite the differences between a five-kingdom and a three-domain system
Systematics: seeks to understand evolutionary history of live. It is very analytical and relies on a
combination of data from the fossil record and comparative anatomy and development, and molecular
data to reconstruct phylogeny (the evolutionary history of a group or organisms). Classification is ONE
PART of systematics.
1. Linnean Classification
a. Taxonomy: the branch of biology concerned with identifying, naming, and classifying
organisms
b. Binomial system of nomenclature (naming) of genus and species e.g. Homo sapien
c. Linnean Levels: species, genus, family, order, class, phylum, and kingdom
d. New addition: domain (higher than kingdom)
e. Each level/category can be subdivided into three additional levels (superorder, order,
suborder, infraorder)
f. More than 30 levels/category of classification
g. This is STILL how we name organisms
2. Polygenetics
a. Modern way to classify animals and build evolutionary trees
b. Arrange species and higher classification categories into clades
c. Clades: contain a most recent common ancestor and all its descendent species;
pictured in a cladogram
d. Convergent evolution: (converge = to come together)
i. the acquisition of the same or similar traits in distantly related lines of descent
ii. analogous structures: (e.g. bat wings and insect wings) have the same function
but the two organisms do NOT share a common ancestor
iii. homologous structures: structure that is similar in two or more organisms due
to common ancestry (e.g. Figure 27.8 on p.549)
e. Parsimony:
i. Traditional method of classifying with phylogenetics
ii. the pattern that requires the fewest evolutionary changes is most likely
f. Decisions today about how closely organisms are related is based on DNA or rRNA
sequences
g. Linnean Classification vs. Phylogenetics
i. Traditional Linnean classification is often inconsistent with new understandings
(based on DNA and rRNA sequences) of phylogenetics
ii. New classification system proposed: “International Colde of Phylogenetic
Nomenclature” or “PhyloCode” for short
1. Naming based on clades instead of traditional Linnean levels
iii. Other option: modify Linnean classification to be consistent with new findings
from phylogenetics
h. Two major unsolvable problems:
i. Clades are hierarchically arranged as are Linnean categories, but there are
MANY more clades than Linnean taxonomic categories
ii. Taxonomic groups are not necessarily equivalent in the Linnean system
3. Three Domain Classification System
a. Traditionally, five kingdom system used (animals, plants, fungi, protists, and monerans)
b. Kingdom designation based on:
i. cell type (prokaryote vs. eukaryote)
ii. Level of organization (multicellular or unicellular)
iii. Type of nutrition
c. DNA sequencing lead to questions as to this classification system
i. Two groups of prokaryotes: archaea and bacteria  given new classification of
domain
d. Domain is a higher classification than Kingdom
e. New levels: (from lowest to highest) species, genus, family, order, class, phylum, and
kingdom, domain
f. Three Domains:
i. Archaea
ii. Bacteria
iii. Eukarya (contains protists, animals, fungi, and plants)
Check Your Progress p.565 #1-3
Chapter 27 Review Guide
1. Make sure you have completed all the “Check Your Progress” questions in the chapter
2. Make sure you have completed the 27.2 “Guided Reading” questions
3. Watch “Evolutionary Arms Race” on Tuesday, May 1 in class and answer these questions:
a. Explain what is meant by “our [humans] spiraling arms race with microorganisms”.
b. Trace the alarming spread of resistance among pathogens (things that do us harm – like
viruses and some bacteria, for example
4. Read p.566 for an excellent summary of the chapter
5. Reread your notes (handouts and self-made)
6. Answer p.567 #1-16
7. Review p.568 terms – look up any that you don’t understand. Most of these have been bolded
in your class hand-outs
8. “Thinking Critically” p.568 #1-3 are excellent candidates for long answer questions
9. “As the Worm Turns” – be able to use the 8 species isolation mechanisms and mechanisms of
speciation (allopatric, sympatric, parapatric) to analyze whether two groups of organisms are
the same or different species.