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This is Panorpa japonica. Commonly known as the
scorpion fly.
Carolus Linnaeus
 Created the classification
system and binomial
 Taxonomy is the
science of naming and
classifying organisms.
 Linnaean taxonomy
classifies organisms
based on their physical
and structural
 Organisms are placed on different levels in which each
level is included in a larger, more general level.
 A group of organisms in a classification system is
called a taxa.
 The most basic taxon is species.
Binomial Nomenclature
 Binomial nomenclature is a
system that gives each species
a two-part scientific name
using Latin words.
 The first part of the name is the
genus, which is always
 The second part of the name is
the species. It is always
Scientific Names
 Why do biologists use scientific names?
 Genera may contain hundred of species that have very
similar common names.
 Scientific names allow scientists to talk about particular
species without confusion.
Linnaeus classification system has seven levels
 From the most general to the most
 Kingdom
 Phylum
 Class
 Order
 Family
 Genus
 Species
Dichotomous Keys
 Dichotomous keys are used to identify organisms through a series
of steps.
 A dichotomous key is made up of paired statements. (di = two)
 Each object fits into one category or the other, but not both.
The Linnaean classification system has limitations.
 The Linnaean system focuses
on physical similarities
 Today, scientists use genetic
research to help classify
 Genetic similarities
between two organisms
are more likely than
physical similarities to be
due to a common ancestor.
 The evolutionary history for a
group of species is called
 To classify species, scientists
look at more than just physical
 They use living species
 the fossil record
 DNA data
 Phylogenies can be shown as
branching tree diagrams.
 Cladistics is classification
based on common
 The goal of cladistics is to place
species in the order in which
they descended from a common
 A cladogram is an evolutionary
tree that proposes how species
may be related to each other
through common ancestors.
Derived Characters
 Derived characters are traits
that can be used to figure out
evolutionary relationships.
 Cladograms are made by
figuring out which derived
characters are shared by
which species.
 The more closely a related
species are, the more derived
characters they will share.
Derived Characters:
Organisms that branch off after a hash
mark share the derived character
represented by the hash mark. A bony
skeleton is a derived character. Sharks
do not have this derived character.
Interpreting a Cladogram
 Derived characters are
shown as hash marks
between the branches of
a cladogram.
 All species above a hash mark
share the derived character it
 This order is hypothesized to
be the order in which they
descended from their common
Derived Characters
Interpreting a Cladogram
 Nodes
 Each place where a branch splits is
called a node.
 Nodes represent the most recent
common ancestor shared by a
 Identifying Clades
 A clade is a group of organisms
that share certain traits derived
from a common ancestor.
In a cladogram, a
node is the
intersection of two
branches. This node
represents the most
recent common
ancestor shared by
the entire
mammalian clade.
A clade is a group
of organisms that
share certain
traits derived
from a common
Molecular evidence reveals species’
 An evolutionary tree is always
a work in process.
 Hormones, proteins, and
genes are all used to help learn
about evolutionary
 DNA is considered to be the
“last word” when figuring out
how related two species are to
each other.
 The more similar to each other
the genes of two species are, the
more closely related the species
are likely to be.
Molecular Clocks
 Molecular clocks are models that
use mutation rates to measure
evolutionary time.
 Mutations are nucleotide
substitutions in DNA, some of
which cause amino acid
substitutions in proteins.
 These mutations tend to add up at a
constant rate for a group of related
 The more time that has passed since two
species have diverged from a common
ancestor, the more mutations will have
built up in each lineage, and the more
different the two species will be at the
molecular level.
Linking molecular data with time.
 Scientists must find links between
molecular data and time.
 A geologic event that is known to have
separated a species allows scientists to
give a real date to the rate of mutation.
 For example: Scientists know that the
marsupials of Australia and those of South
America diverged about 200 million years
ago, when these two continents split.
South American “Monito del Monte”—
Monkey of the Mountains. A marsupial.
 A link can also come from fossil
 Molecular data can be compared to the
first appearance of each type of
organism in the fossil record.
Austrailian bandicoot. A marsupial.
Mitochondrial DNA (mtDNA)
 Mitochondrial DNA is
found only in
 mtDNA is always
inherited from the mother.
 mtDNA is passed down
unshuffled through many
Ribosomal RNA (rRNA)
 Ribosomal RNA is
found only in the
ribosomes of cells.
mutations VERY
Classification is always a work in
 1753—two kingdoms
 Animalia and Plantae
 1866—three kingdoms
 Animalia, Plantae, Protista
 1938—four kingdoms
 Animalia, Plantae, Protista, Monera
 1959—five kingdoms
 Animalia, Plantae, Protista, Monera,
 1977—six kingdoms
 Animalia, Plantae, Protista, Archaea,
Bacteria, Fungi
This is wrong! 
The Three Domains
 All organisms with
eukaryotic cells.
 May be single-celled,
colonial, or
 Includes the
kingdoms Protista,
Plantae, Fungi, and
 Single-celled prokaryotes.
 Cell walls are chemically
different from bacteria—
allows achaea to live in
extreme environments.
 Archaea are found in
deep sea vents, hot
geysers, Antarctic
waters, salt lakes, and in
the middle of volcanoes.
 Single-celled
 Largest groups of
organisms on Earth.
 There are more
bacteria in your
mouth than there
are people that
have ever lived!