Unit 4 – Taxonomy
• In this unit, we look at how biologists classify
organisms into groups.
Taxonomy
• When communicating in science, it is very
important to be specific. Vague terms lead to
misinterpretations, confusion, and disaster.
• For living things, classifying them specifically allows
researchers around the world to be certain they are
dealing with the exact same organism, not a
variant species or alternate strain.
• As well, we can create clearly-defined categories
for life based on their genetic/evolutionary history
and not just appearance.
Linnaean Taxonomy
• The modern system for
naming organisms
owes much to the work
of 18th century
naturalist Carl Linnaeus.
• This system is known as
binomial naming, as
each species has a
two-word name.
Linnaean Taxonomy
• Binomial names include a name of the species in
particular as well as a name of their genus. A genus
is a grouping for closely related species.
• The order goes genus then species.
•
•
•
•
Human – Homo sapiens
Neanderthal - Homo neanderthalensis
Panther – Panthera pardus
Sometimes the genus will be abbreviated - E. coli
Linnaean Taxonomy
• Using this system we can easily identify closelyrelated organisms from their genus.
• The system goes beyond this binomial
nomenclature, there are as many as 8 levels in this
system:
• Domain, Kingdom, Phylum (plural: phyla), Class,
Order, Family, Genus, Species, (Sub-species)
• All of these terms are called taxa (sing. taxon).
Linnaean Taxonomy
• Human:
o
o
o
o
o
o
o
o
Domain – Eukaryota
Kingdom – Animalila
Phylum – Chordata
Class - Mammalia
Order – Primates
Family – Hominidae
Genus – Homo
Species – Sapiens
• Neanderthal:
o Domain – Eukaryota
o Kingdom – Animalila
o Phylum – Chordata
o Class - Mammalia
o Order – Primates
o Family – Hominidae
o Genus – Homo
• Species – neanderthalensis
Linnaean Taxonomy
• Human:
o
o
o
o
o
o
o
o
Domain – Eukaryota
Kingdom – Animalila
Phylum – Chordata
Class - Mammalia
Order – Primates
Family – Hominidae
Genus – Homo
Species – Sapiens
• Dog:
o
o
o
o
o
o
o
o
Domain – Eukaryota
Kingdom – Animalila
Phylum – Chordata
Class - Mammalia
Order – Carnivora
Family – Canidae
Genus – Canis
Species - Lupus
Linnaean Taxonomy
• Human:
o
o
o
o
o
o
o
o
Domain – Eukaryota
Kingdom – Animalila
Phylum – Chordata
Class - Mammalia
Order – Primates
Family – Hominidae
Genus – Homo
Species – Sapiens
• E. coli:
o
o
o
o
o
o
o
o
Domain – Bacteria
Kingdom – Bacteria
Phylum – Proteobacteria
Class - Gammaproteobacteria
Order – Enterobacteriales
Family – Enterobacteriaceae
Genus – Escherichia
Species - Coli
Models of Diversity
• One of the oldest
questions of biology
involves how species
have changed and
diverged from each
other throughout time.
• Most traditional models
show life originating
from a common
ancestor which over
time diverged into all
organisms we now
know.
Models of Diversity
• Scientists often
organize the
divergence of life in a
tree diagram.
• However, it is important
to realize that species
near the top are not
inherently superior, they
are just simply more
recent occurances.
Five Kingdom Model (Old)
• One model to group organisms is the Five
Kingdom Model. Up until recently, this was the
generally accepted classification system. Here,
life was grouped at the highest level into five
kingdoms.
•
•
•
•
•
Monera
Protista
Fungi
Plantae
Animalia
Five Kingdom Model (Old)
• Monera: all prokaryotic organisms.
• Fungi: eukaryotes that decompose their food externally
and absorb it.
• Plantae: photosynthetic eukaryotes that build foodstuffs
using light energy.
• Animalia: eukaryotes that feed by consuming other
organisms.
• Protista: all single-celled eukaryotic organisms. (basically
all eukaryotes that are not fungi, plants or animals)
Five Kingdom Model (Old)
• The five kingdom model had two main
problems.
• First, the kingdom monera contained all
prokaryotes, despite the fact that prokaryotes
are a very diverse group.
• Grouping all of these diverse organisms into one
group was forcing species together who are
actually unrelated.
Five Kingdom Model (Old)
• In particular, the two major groups of
prokaryotes, bacteria and archaea were
discovered to have very different evolutionary
histories.
• Archaea have been discovered to have more
in common with eukaryotes than bacteria,
evolutionarily despite still being prokaryotes.
Five Kingdom Model (Old)
• The modern
interpretation is that
bacteria diverged off
from other life earlier
than archaea,
leaving more in
common between
archaeans and
eukaryotes.
Five Kingdom Model (Old)
• In the end, archaea are not only very different
from their fellow prokaryotes the bacteria but
are simply unique in general.
• Thus, the kingdom monera is a bad label as it
groups two very different groups together.
Five Kingdom Model (Old)
• The other main problem with kingdom system
involves the kingdom Protista.
• Again, this category involves combining too
many diverse creatures into one group – it gives
a false sense of relatedness.
• Protists are mashed together despite very
different metabolisms, life cycles and
development.
Three Domain Model
• To address these
issues, a new three
domain model was
introduced. Domains
are now the highest
level, with kingdoms
below.
Three Domain Model
• In the three domain
system, the large
evolutionary
differences between
prokaryotes is
addressed by
replacing monera
with the Archaea
and Bacteria
domains.
Three Domain Model
• The four eukaryotic
kingdoms now belong
under the Eukarya
domain.
• Protists still remain
somewhat forced into
a group, but they are
more often grouped by
their phyla now rather
than by the group
“protist” as a catch-all.
Ring of Life Model
• Recently, the idea that early life evolved linearly
with species branching off and off has come in
question.
• Many scientists now propose that early life
would have been more similar than it is now
and thus sharing DNA between species was
more common.
• Thus rather than branching straight off, early
species made be interrelated on many, many
levels.
Ring of Life Model
• The ring of life model
basically proposes that
very early on life forms
shared genetic
information significantly
more than now. This forms
a interconnected ring of
relationships between
early life forms.
• Later, species would
begin to diverge away
from the ring and into the
separate categories we
have today.
Origin(s) of Life on Earth
• In the end, finding a model to fit the development of life
on earth may involve mixing one or more theories. The
fact that early life does not as readily fossilize as large,
modern species only further makes the past harder to
observe.
• There are also some evidence that life on Earth may not
have began on Earth but instead have been seeded by
small microbes arriving by meteors.
• Given the problems in finding evidence of these old life
forms, we may never know the specifics of the early life
on this planet.
Video
• http://www.youtube.com/watch?v=F38BmgPcZ_I