The Living World
Fifth Edition
George B. Johnson
Jonathan B. Losos
Chapter 18
Exploring Biological Diversity
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
18.1 The Invention of the Linnaean
System
• To talk about and to study organisms it is
necessary to give them names
 biologists use a kind of multilevel grouping of
individuals called classification
 the earliest classification scheme grouped
animals and plants into basic units called
genera (singular, genus)
• early biologists added a series of non-standardized
descriptions to the genus name
• this created a string of subjective names called a
polynomial
18.1 The Invention of the Linnaean
System
• A much simpler system than the
polynomial for the naming of organisms
was developed by Carolus Linnaeus
 Linnaeus assigned organisms a two-part
name called a binomial
 he also grouped similar organisms into
higher-level categories based on similar
characteristics
• this would have important, though unintended,
applications to evolutionary connections
Figure 18.1 How Linnaeus named
two species of oaks
18.2 Species Names
• Taxon (plural, taxa) is a group of
organisms at a particular level in a
classification system
 the branch of biology that identifies and
names such groups is called taxonomy
 no two kinds of organisms can have the same
name and all names are given in Latin
18.2 Species Names
• The scientific name for an organism is
comprised of the two-part binomial
 the first part is the genus, which is always
capitalized
 the second part is the specific epithet and is
not capitalized
 the two words together are written in italics or
underlined
18.3 Higher Categories
• the binomial has been expanded into a Linnaean
system of classification
 genera with similar properties are grouped together into a family
 families that share similar characteristics are put into the same
order
 orders with common properties are placed into the same class
 classes with similar characteristics are placed into the same
phylum
 phyla are assigned to one of several gigantic groups called
kingdoms
 kingdoms are sometimes assigned to an additional level of
classification, called domains
Figure 18.3 The hierarchical system
used to classify an organism
18.4 What Is a Species?
• Since the time of Linnaeus, about 1.5 million
species have been named
 the actual number of species is much greater
 the biological species concept is widely applied to
animals but not as frequently to plants
• it does not apply to some kingdoms at all
 molecular data are causing a reevaluation of
traditional classification systems
18.5 How to Build a Family Tree
• Phylogeny is the evolutionary history of
an organism and its relationship to other
species
• Systematics is the study of and
reconstruction of phylogenetic trees
 it also includes the naming and classifying of
organisms
18.5 How to Build a Family Tree
• Cladistics is the systematic approach that infers
phylogeny according to similarities derived from a
common ancestor
 derived characters are characters that are present in a group of
organisms that arose from a common ancestor that lacked the
character
• a clade is a group of organisms, related by descent, that share a
derived character
 by examining the distribution of derived traits among related
organisms, it is possible to construct a cladogram, a branching
diagram that represents the phylogeny
Figure 18.5 A cladogram of
vertebrate animals
18.5 How to Build a Family Tree
• Cladograms convey comparative information
about relative relationships
 organisms that are closer together on a cladogram
simply share a more recent common ancestor than
those that are farther apart
 each cladogram must have an outgroup, a rather
different organism to serve as a basis for
comparisons among the other organisms being
evaluated, called the ingroup
18.5 How to Build a Family Tree
• Cladistics is a relatively new but popular
approach to studying evolution because it
is objective and portrays the order in which
a series of evolutionary events have
occurred
18.5 How to Build a Family Tree
• An alternative approach to constructing
phylogenies is traditional taxonomy
 both ancestral and derived characters are
used to build trees
• this wealth of additional information is often
weighted by its biological significance but this is a
more subjective process than cladisitics
Figure 18.6 Two ways to classify
terrestrial vertebrates
18.6 The Kingdoms of Life
• Most biologists use a six-kingdom system first proposed
by Carl Woese
 four kingdoms consist of eukaryotes
• Animalia, Plantae, Fungi, and Protista
 two kingdoms consist of prokaryotes
• Archaea and Bacteria
• Recognizing that there are further differences among the
prokaryotes, the domain level above kingdom was
created
 Domain Archaea contains the Kingdom Archaea
 Domain Bacteria contains the Kingdom Bacteria
 Domain Eukarya contains the eukaryotic kingdoms
Figure 18.8 Different approaches to
classifying living organisms
18.7 Domain Bacteria
• The bacteria are the most abundant
organisms on earth
 there are many different types of bacteria and
the evolutionary links between them are not
well understood
• most taxonomists recognize 12 to 15 major groups
of bacteria
• although archaea are also prokaryotic like bacteria,
the archaea are more closely related to eukaryotes
18.8 Domain Archaea
• The Archaea branched off from a line of
prokaryotic ancestors that lead to the evolution
of eukaryotes
 modern Archaea live in some of the most extreme
environments on earth and, although a diverse group,
share some of the same key characteristics
• their cell walls lack the peptidoglycan that is characteristic of
bacterial cell walls
• they possess unique lipids and rRNA sequences
• some genes in the archaea have introns
Figure 18.9 A tree of life
18.8 Domain Archaea
• Archaea are grouped into three general
categories
 methanogens obtain their energy by using hydrogen
gas (H2) to reduce CO2 to methane gase (CH4)
 extremophiles are able to grow under extreme
conditions, such as extreme heat, salt, pH or pressure
 nonextreme archaea grow in the same environments
that bacteria do
18.9 Domain Eukarya
• Eukaryotes have a complex cellular
organization but are fairly uniform in
metabolism, when compared to
prokaryotes
 there are three largely multicellular kingdoms
(fungi, plants, and animals)
 the remaining eukaryotic kingdom, Protista, is
a diverse array of mostly unicellular forms that
basically don’t fit into the other kingdoms
18.9 Domain Eukarya
• Endosymbiosis may explain the origin of
eukaryotes from prokaryotes
Figure 18.11 Endosymbiosis
Inquiry & Analysis
• Three great
innovations in the jaw
and tail occur during
the history of the bony
fishes, producing the
superorders
represented by
strurgeons, then gars,
then teleost fishes. In
what period did each
innovation occur?
Graph of The Rate New Forms of
Fish Have Appeared