Classification
CHAPTER 18
MS. LUACES
HONORS BIOLOGY
Finding Order In Diversity – 18.1
 How do we order species?
 Has this order changed over time?
 Will this order continue to change?
Assigning Scientific Names
 First step: describe and give a universally accepted
name to each species
 One of the easiest ways to classify is using a
dichotomous key – following a set of steps /
questions to arrive at a conclusion
Let’s Practice
 Copy the table below and choose 4 ways to categorize
the fruits with members at your table
Fruit
Apple
Pear
Orange
Kiwi
??
??
??
Assigning Scientific Names
 Linnaeus invented a system of binomial
nomenclature – scientific name consisting of Genus
species
Assigning Scientific Names
 The goal of
systematics is to
organize living
things into groups
that have biological
meaning – higher
than Genus species
The Linnaean Classification System
 Linnaeus went from developing a system with 4
groups to one with seven hierarchical taxa:
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Kingdom
Phylum
Class
Order
Family
Genus
Species
The Linnaean Classification System
 As you down the ladder of classification, you get
more specific. We go from classifying according to
general similarities, to specifics and interbreeding
capabilities
 Kingdom looks at generalities (are you multicellular?) while species looks at specifics (what’s
special about you?)
The Linnaean Classification System
 However, how do we decide which similarities and
differences are most important?
 Linnaeus used only similarities and differences with
other living organisms. Today, we also look at where
in the evolutionary tree does the organism belong
and its DNA.
Modern Evolutionary Classification – 18.2
 Linnaean classification had some faults under
Darwin’s theory of evolution… the “tree of life” did
not fit under it

How do we re-organize our classification to fit molecular
evidence?
Evolutionary Classification
 The goal of phylogenetic systematics (evolutionary
classification) is to group species into larger
categories that reflect the lines of evolutionary
descent, rather than similarities or differences
Evolutionary Classification
 Common ancestors – as we go into higher taxa, we
get closer to our common ancestor
 Clades – include a common ancestor and all of its
descendants

Known as monophyletic – ‘mono’ meaning one ancestor
Cladograms
 A cladogram links groups of organisms by showing
how evolutionary lines, or lineages, branched off
from common ancestors
Cladograms
 When one species splits off into two (think the
finches), we call that a node in a cladogram. That
point represents the last point at which two lineages
shared a common ancestor
Cladograms
 The bottom, or “root” of the cladogram represents
the common ancestor
 Each branching pattern gives the degree of
relatedness between the organisms
Cladograms
 Cladograms depend on derived characteristics (a
trait that arose in a recent common ancestor in a
particular lineage) while Linnaean only grouped on
similarities

Sometimes traits are lost in the process of evolution, but it still
links them together!
Interpreting Cladograms
 The lowest node represents the last common
ancestor
 Each derived character listed along the main trunk of
the cladogram defines a clade

Ex: retractable claws are only shared by Felidae (cats)
Interpreting Cladograms
 So where do Linnaeus and cladograms meet?
 Remember cladograms include the common ancestor and ALL
its descendants
 For example, birds do not fit into the traditional Linnaean
taxonomy, but they are reptiles! (come from the same common
ancestor).
DNA in Classification
 When organisms don’t have similar physical
characteristics, we turn to DNA to help us classify
them.

In general, the more derived genetic characters two species
share, the more recently they shared a common ancestor and
the more closely they are related in evolutionary terms.
DNA in Classification
 Example: the Red Panda is more closely related to
raccoons than it is to Giant Pandas and Bears

Completely different genus! All this information from DNA.
18.2 – Let’s Practice
 Study Workbook A Pgs. 205-206
 Work with a buddy (one sheet of paper). Write the
question AND the answer
 No key concepts
 Due at the end of class!
18.3 Building The Tree Of Life
 Kingdoms in the 1700’s consisted only of Plantae and
Animalia. Today, we have 6 Kingdoms:
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Eubacteria
Archaebacteria
Protista
Fungi
Plantae
Animalia
18.3 Changing Ideas About Kingdoms
 As research became more readily available, the
kingdoms went expanding according to different
characteristics each of the cells exhibited
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Pg. 524, Figure 18-14 should be copied in your notes!
18.3 Changing Ideas About Kingdoms
 Kingdoms were not the only ones to change –
Domains changed too!

Went from Eukaryotes and Prokaryotes to Eubacteria,
Archaebacteria and Eukarya
18.3 The Tree Of Life
 The tree of life shows current hypotheses regarding
evolutionary relationships among the taxa within the
three domains of life
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It is not fact or permanent, it’s constantly changing as we
discover new things!
18.3 The Tree Of Life
 Domain Bacteria:
 Unicellular
 Prokaryotic
 Thick cell walls with
peptidoglycan
 Can use photosynthesis
or oxygen (or not)
 Kingdom Eubacteria
18.3 The Tree Of Life
 Domain Archaea:
 Unicellular
 Prokaryotic
 Extremophiles
 Anaerobic (no oxygen)
 Cell walls with no
peptidoglycan
 Kingdom Archaebacteria
18.3 The Tree Of Life
 Domain Eukarya:
 Have nucleus
 Kingdom Protista
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Kingdom Fungi
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Heterotrophs who feed on decaying matter and have chitin in their
cell walls
Kingdom Plantae
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Many different characteristics (uni / multicellular,
anaerobic/aerobic) and paraphyletic (not a true clade)
Autotrophs that have cellulose in their cell walls and do
photosynthesis
Kingdom Animalia

Multicellular and heterotrophic with no cell walls
Let’s Practice!
 Study Workbook A Pgs. 207-209
 One sheet of paper for both of you, QUESTION &
ANSWER
 No key concepts
 Due at the end of class!