History of Classification
Finding Order in Diversity
History of Classification
• For more than 3.5 billion years, life on Earth
has been constantly changing.
• Natural Selection has led to a staggering
diversity of organisms.
• Biologists have identified and named about
1.5 million species so far
• Estimate that 2 and 100 million have not yet
been discovered.
Classification
1. Why classify?
a. By using a scientific name,
biologists can be certain
that everyone is discussing
the same animal.
b. Taxonomy
• A discipline of classifying
organisms and assigning each
organism a universally
accepted name.
History of Classification
2. How are living things
organized for study?
a. When you hear the
word “bird”, what
mental picture appears?
• A flying animal that has
feathers
History of Classification
b. In a good system of classification, organisms
placed into a particular group are more
similar to each other than they are to other
organisms in different group.
– EX: We use a classification system. When you
refer to “teachers”, or more specifically “zoology
teachers”.
History of Classification
c. By the 18th century, European scientists realized
that referring to organisms by common names
was confusing. Common names vary among
languages.
– For example a cougar can also be called a puma, a
panther or a mountain lion.
History of Classification
• In England, the word buzzard refers to a hawk
whereas in many parts of the US, buzzard
refers to a vulture.
History of Classification
Aristotle’s System
1. The first attempt at standardizing scientific
names basically described the physical
characteristics of a species.
– EX: scientific name of a particular tree might be
“Oak with deeply divided leaves that have no hairs
on their undersides and no teeth around their
edges.”
History of Classification
Carolus Linnaeus
• Swedish botanist who
lived during the 18th
century.
– binomial nomenclature
• Classification system
in which each species
is assigned a two-part
scientific name.
1. Linnaeus’s System of Classification
• Classification system
with 7 levels
• Each level called taxon
(plural: taxa)
• Why 7 levels?
– Lots of organisms
Classification System
• Kingdom
Phylum
Class
Order
Family
Genus
Species
• Country
State
County
City
Neighborhood
Street
House #
Kingdom
• Largest taxonomic group,
consisting of closely
related phyla
– Eukaryotes
• 2 original kingdoms
– Animalia
– Plantae
Phylum
• Group of closely
related organisms that
share important
characteristics
• Ex: Chordata –
Humans & Bears
Class & Order
• Class – group of similar orders
– Mammalia
• Internal regulation of body
temp. (warm-blooded)
• Have body hair
• Produce milk for young
• Order – broad taxonomic
category composed of similar
families
– Carnivora
• Bears - Ursidae
• Dogs – Canidae
• Cats - felidae
Family
• Share many
characteristics
• EX: Bears – Ursidae
and Ailuropoda
– Polar bears
– Grizzly bears
– Panda bear
Genus & Species
• Genus
– Group of closely related species, and the first part of the
scientific name in binomial nomenclature.
• Species
– Group of organisms that can breed and produce offspring
that are fertile.
Grizzly Bear
Ursus arctos
Polar Bear
Ursus maritimus
Giant Panda
Ailuropoda melanoleuca
Binomial Nomenclature
• 2-word naming system
• Each species is assigned
a 2 part name
• Always written in italics
or underlined
– First word is always
capitalized
– Genus species
Grizzly bear ~ Ursus arctos
Questions???
• How are organisms classified?
– Living things are classified according to shared
characteristics and organized into 7 categories.
• What is binomial nomenclature?
– A two-word naming system
• Explain the difference between Aristotle’s system and
Linnaeus's system of classification?
– Aristotle’s common name system which can differ due to
in languages.
– Linnaeus’s system of binomial nomenclature
Modern Evolutionary
Classification
What characteristics do scientists use
to classify organisms?
Modern Classification
• Organisms choose with whom they will mate.
• Group organisms according to biologically
important characteristics.
• Linnaeus’s system grouped animals according
to visible similarities and differences.
– Problems???
Modern Classification
• How would you classify the crab, limpet, and
barnacle?
Look more closely!
LIMPET
BARNACLE
Limpet and barnacle larvae are very different.
Barnacles have jointed limbs.
Limpets DON’T !
Barnacles have a segmented body
Limpets DON’T !
Barnacles have an exoskeleton that molts.
Limpets DON’T !
CRAB
Look more closely!
LIMPET
CRAB
BARNACLE
Crab and barnacle larvae are very similar
Barnacles have jointed limbs.
So do CRABS !
Barnacles have a segmented body
So do CRABS !
Barnacles have an exoskeleton that molts.
So do CRABS !
Modern Classification
Modern Classification
Evolutionary Classification
• Darwin’s ideas about descent with modification
gave rise to the study of phylogeny.
– The study of evolutionary relationships among
organisms.
Evolutionary relationship of
the Phylum Chordata
Modern Classification
• Evolutionary classification
– Method of grouping organisms together according
to their evolutionary history.
– All members of a genus share a recent common
ancestor.
Modern Classification
• Cladogram
– Diagram that shows
the evolutionary
relationships among
a group of
organisms.
• Derived character
– Characteristic that
appears in recent
parts of a lineage, but
not in its older
members.
Derived
Characters
Modern Classification
• Similarities in DNA and RNA
– Genes of many organisms show important
similarities.
– DNA can be used to determine classification and
evolutionary relationships.
Are these organisms related?
Similarities in DNA can be used to help show
evolutionary relationships and how species have
changed.
African vulture
American vulture
Stork
Traditionally these first two were
classified together in falcon family.
Storks were put in a separate family.
American vultures have a peculiar behavior. When
they get overheated, they urinate on their legs to
cool off
African vulture
American vulture
Stork
The only other bird that does this is the
STORK.
DNA comparisons showed more similarities
between American vulture and stork DNA than
DNA from the two kinds of vultures suggesting a
more recent common ancestor between storks
and American vultures.
African vulture
American vulture
Stork
Questions???
1. What characteristics do scientists use to classify
organisms.
–
Biological:
•
•
•
–
Structure (including similarities in DNA)
Physiological
behavioral
Evolutionary relationships; phylogeny
2. How are evolutionary relationships important in
classification?
–
Accurate placement of organisms within their phylogenic
tree.
Domains and Kingdoms
What are the three-domain systems of classification?
• Bacteria
•Archae
•Eukaryota
3 Domain System
• Modern organisms have
been grouped according to
how evolved
• Domain
– More inclusive category;
larger than a kingdom.
• 3 Domains:
1. Bacteria – unicellular &
prokaryotic
2. Archaea - extremophiles
3. Eukarya – unicellular &
multicellular Eukaryotes
3 Domain System
1. Eubacteria
– Domain of unicellular prokaryotes that have cell
walls containing peptidoglycans
3 Domain System
2. Archaea
•
•
Domain of unicellular prokaryotes that have cell
walls that do not contain peptidoglycan
They live in extreme environments.
Colonies of haloarchaea on agar plates
3 Domain System
3. Eukarya
 Domain of all organisms whose cells have nuclei,
including protists, plants, fungi and animals.
Tree of Life
6 Kingdoms of Life
• The six-kingdom
system of classification
includes:
1.
2.
3.
4.
5.
6.
Eubacteria
Archaebacteria
Protista
Fungi
Plantae
Animalia
Domain Eukarya
Kingdom Protista
• The kingdom Protista is composed of eukaryotic
organisms that cannot be classified as animals,
plants or fungi,
• They can be unicellular or multicellular;
photosynthetic or heterotrophic; and can share
characteristics with plants, fungi or animals.
Kingdom Fungi
• Kingdom composed of heterotrophs; many
obtain energy and nutrients from dead
organic matter (decomposers).
• They can be either multicellular (mushrooms)
or unicellular (yeasts).
Kingdom Plantae
• Members of the Kingdom Plantae are
multicellular, photosynthetic autotrophs that
have cell walls containing cellulose.
• Plants are nonmotile – they cannot move from
place to place.
Kingdom Animalia
• Members of the Kingdom Animalia are
multicellular eukaryotic heterotrophs
whose cells do not have cell walls.
• There is great diversity within the animal
kingdom, and many species exist in nearly
every part of the world.
Questions???
1. What are the three-domain systems of
classification?
– Bacteria, Archae and Eukarya
2. What are the six kingdoms of life?
•
Eubacteria, Archaebacteria, Protista, Fungi, Plantae,
Animalia