CH.18
CLASSIFICATION
Bianca Hernandez
Biology Honors P6
11 April 2014
THINK ABOUT IT
Scientists have been trying to
identify, name, and find order in
our diverse earth for a long time,
which has led us to classification.
Key Questions
What are the goals of binomial
nomenclature and systematics?
How did Linnaeus group species
into larger taxa?
18.1 FINDING ORDER
IN DIVERSITY
ASSIGNING SCIENTIFIC NAMES
• 1) understanding + studying diversity
• describe and name each species, which is useful b/c if we refer to
each species by one name only, everyone will use the name
• what type of name?
• Sometimes be misinterpreted b/c variations in languages and
places , which leads to different species sharing common names
• 18th century began the use of Latin/Greek names per species
• Dichotomous Key
• Used to identify organisms
• 1) using series of paired statements, which will describe alternative
possible characteristics of an organism
• 2) paired statements which usually describe presence or absence
of certain visible characteristics/structures
• 3) entire processes leads into subsets until you achieve the desired
outcome
Ex. Of Dichotomous Key
BINOMIAL NOMENCLATURE
• Carolus Linnaeus developed the binomial nomenclature – a
two-word naming system
 Each species is assigned a two-part scientific name
 1) scientific names are written in italic
 2) 1 word = C ; 2 word = c
 3) the first part is the genus and the second is the species
• Genus – a group of similar species
• Species – description of an important trait / an organism’s
habitat
BINOMIAL NOMENCLATURE
RED MAPLE
SCIENTIFIC NAME = Acer rubrum
GENUS Acer = CONSIST OF ALL
MAPLE TREES
SPECIES rubrum = RED MAPLE
COLOR
CLASSIFYING SPECIES INTO LARGER GROUPS
 try to organize/classify living and fossil species into larger groups
that will have a biological meaning
• Systematics – science of naming and grouping organisms
• These groups are referred to as – taxa
• Ex. Professor
• Science Professor
THE LINNAEAN CLASSIFICATION SYSTEM
• Linnaeus developed a classification system that organized
species into taxa that formed a hierarchy/set of ordered ranks
 Seven hierarchical taxa: Species, Genus, Family, Order, Class,
Phylum, and Kingdom
• He grouped species according to anatomical similarities and
differences
• Family – where several genera that share many similarities are
grouped into a larger category
• Order – closely related families are grouped into the next larger
rank
• Class – similar orders are grouped
• Phylum – classes are grouped; includes organisms that are
different but share important characteristics
• Kingdom – largest and most inclusive rank
• (K)ing (P)hilip (C)ame (O)ver (F)or (G)ravy (S)oup
PROBLEMS WITH TRADITIONAL CLASSIFICATION
• In a sense, members of a species determine which organisms belong to
that species by deciding with whom they mate and produce fertile
offspring, which mean there is a “natural” definition of species
• Researchers define Linnaean ranks above the level of species b/c over
time systematics have emphasized a variety of characteristics and some
of these groups have been defined in different ways at different levels
• Ex. Linnaean’s classification of organisms according to visible similarities
and differences
• Modern systematics apply Darwin’s ideas to classification and also try to
look beyond simple similarities and differences so thy can ask questions
about evolutionary relationships
Key Questions
What is the goal of evolutionary
classification?
What is a cladogram?
How are DNA sequences used in
classification?
18.2 MODERN
EVOLUTIONARY
CLASSIFICATION
EVOLUTIONARY CLASSIFICATION
• The concept of descent with modification led to the study
of phylogeny – the evolutionary history of lineages
• Advances in phylogeny led to phylogenetic systematics
Goal is to group species into larger categories that reflect
lines of evolutionary descent, rather than overall
similarities and differences
COMMON ANCESTORS
• Phylogenetic systematics places organisms into higher
taxa whose members are more closely related to one
another
• The larger the taxon is, the further back in time all of
its members shared a common ancestor
CLADES
• Classifying organisms according to these rules places them into
groups called clades – group of species that includes a single
common ancestor and all descendants of that ancestor which
include living and extinct
• How are clades different from Linnaean taxa?
• Clade must be a monophyletic group – includes a single common
ancestor and its descendants
• Some groups of organisms before the arrival are monophyletic
• Some are paraphyletic – the group includes a common ancestor
but excludes one or more groups of descendants, which means
those excluded groups are invalid under evolutionary classification
Ex. Of Mono/Paraphyletic taxon
CLADOGRAMS
• Modern evolutionary classification use a method called cladistics
analysis, which compares carefully selected traits to determine
the order in which groups of organisms branched off from their
common ancestors
 Cladogram – links groups of organisms by showing how
evolutionary lines, or lineages, branched off from common
ancestors
• How do you build a cladogram?
• 1) the diagram shows a single ancestral lineages splitting into two
• The point splitting is the node – represents the last point which
the two new linages shared a common ancestor
• 2) the bottom, or root – the common ancestor shared by all the
organisms
• 3) a cladogram’s branching patterns indicate the degree of
relatedness among organisms
Different Types of Cladograms
Ex. of Cladogram
Ex. of Cladogram
DERIVED CHARACTERISTICS
• In contrast to Linnaean taxonomy, cladistic analysis focuses on
certain kinds of characters, or derived characteristics when
assigning organisms into clades
• Derived characteristics – a trait that arose in the most recent
common ancestor of a particular lineage and was passed along to
its descendants
LOSING TRAITS
• Ex. Clade Tetrapoda have a derived character of four limbs
• Snakes are part of this clade but are not four limbed
• How does this work?
• The ancestors of the snakes did have four limbs, but somewhere
in the lineage that lead to our modern snake, the trait was lost
• Because distantly related groups of organisms can sometimes lose
the same character, systematics are very cautious about using the
absence of a trait as a character in their analysis
• You may ask what about whales since they are also not four
limbed, but we can clearly tell snakes are more closely related to
other reptiles than whales!
INTERPRETING CLADOGRAMS
• 1) the lowest node represents the last common ancestor
• 2) the forks in the cladogram show the order in which various groups
branched off
• 3) the positions of various characteristics in the cladogram reflect the
order in which those characteristics arose in the lineage
• 4) each derived character listed along the main truck of the cladogram
defines a clade
• 5) derived characters that occur “lower” on the cladogram than the
branch point for the clade are not derived for that particular clade
Ex. of Cladogram
DNA IN CLASSIFICATION: GENES AS DERIVED
CHARACTERS
• Since all genes mutate over time, shared genes contain
differences that can be treated as derived characters
• Similarities and differences in DNA con be used to develop
hypotheses about evolutionary relationships
 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
NEW TECHNIQUES SUGGEST NEW TREES
• The use of DNA characters in cladistic analysis has helped to make
evolutionary trees more accurate
• Ex. The hooded vulture from Africa, the American vulture, and Storks
• Both the hooded and American vultures are in the falcon clade
• But American vultures do something odd when they overheat
• They urinate on their legs, as they rely on the evaporation to cool them
down
• Storks also do this, which has led Biologists to try and piece this puzzle
together
• Molecular analysis shows that the DNA from the American vulture is
more similar to storks than African vultures
• Suggests that American vultures and storks share a more recent
common ancestor than American and African vultures
• Molecular analysis is a powerful tool that is now routinely used by
taxonomists to supplement data from anatomy
Key Questions
What are the six kingdoms of
life as they are now identified?
What does the tree of life
show?
18.3 BUILDING THE
TREE OF LIFE
CHANGING IDEAS ABOUT KINGDOMS
• Biologists learned that the two kingdoms – Animalia and Plantae
– did not reflect the full diversity of life
• Five Kingdoms
• Researchers began to study microorganisms which led to the
discovery that single-celled organisms were significantly different
from plants and animals
• They then placed all microorganisms into the kingdom Protista
• Next, they placed yeast and molds + mushrooms into the kingdom
Fungi
• Scientists realized that bacteria lack nuclei, mitochondria, and
chloroplasts that were found in other forms of life = prokaryotes
(bacteria) placed in Monera
CHANGING IDEAS ABOUT KINGDOMS
• Six Kingdoms
• In the 1990’s, researchers realized that the organisms in Kingdom
Monera were actually two genetically and biochemically different
groups
• This led to separating Monera into Eubacteria and Archaebacteria
 Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia
• Three Domains
• Domain – a larger, more inclusive category than a kingdom
• 3 Domains are: Domain Bacteria, which corresponds to kingdom Eubacteria,
Domain Archaea, which corresponds with kingdom Archaebacteria, and
Domain Eukarya, which corresponds with kingdoms Fungi, Plantae, Animalia,
and “Protista”
• There are quotations around Protista b/c it’s a paraphyletic group and there is
no way to put all unicellular eukaryotes into a clade that contains a single
common ancestor, all of its descendants, and only those descendants
THE TREE OF LIFE
• Modern evolutionary classification is a rapidly changing science with
the difficult goal of presenting all life on a single evolutionary tree
• Biologists regularly change not only the way organisms are grouped,
but also sometimes the names of groups
• Different from cladograms b/c they are visual presentations of
hypotheses about relationships, and not hard fact
 Shows current hypotheses regarding evolutionary relationships among
the taxa within the three domains of life
• Domain Bacteria
• Bacteria – unicellular and prokaryotic
• Cells have thick, rigid walls that surround a cell membrane
• Cell walls contain a substance known as peptidoglycan
• They are ecologically diverse, ranging from free-living soil organisms to
deadly parasites
• Some photosynthesize, while others don’t and some need oxygen to
survive while, others are killed by oxygen
THE TREE OF LIFE
• Domain Archaea
• Archaea – unicellular prokaryotes
• Their cell walls do not contain peptidoglycan
• Live in extreme environments such as: volcanic hot springs, brine
pools, and black organic mud that is totally lacking oxygen
• Some of them can only survive in the absence of oxygen
• Cell membranes contain unusual lipids not found in any other
organisms
• Domain Eukarya
• Eukarya – all organisms that have a nucleus
• “Protists” – Unicellular Eukaryotes
• Some people still use the name “protists” for these organisms, but
scientists have known for years that they do not have a valid clade
THE TREE OF LIFE
• Domain Eukarya
• Fungi
• Heterotrophs with cell walls containing chitin
• Most feed on dead or decaying organic matter
• Fungi secrete digestive enzymes into their food source to absorb the small
molecules into their bodies
• Plantae
• Autotrophs with cell walls that contain cellulose
• Can carry out photosynthesis
• Cannot move from place to place
• Animalia
• Multicellular and heterotrophic
• Animal cells do not have cell walls
• Most can move
CREDITS
• Miller & Levine Biology ( ©2010)
• http://www.youtube.com/watch?v=F38BmgPcZ_I
• http://evolution.berkeley.edu/evosite/evo101/IIDClassification.shtml
• http://www.ucmp.berkeley.edu/clad/clad5.html
• http://www.ucmp.berkeley.edu/glossary/gloss1/phyly.html
• http://www.ucmp.berkeley.edu/clad/clad5.html