“The most meaningful groups are based on the study
of evolutionary relationships among organisms.” Raven
CLADOGRAMS
Systematics
• Reconstruction and
study of evolutionary
relationships.
• Can be used to create a
phylogeny or evolutionary
tree
• Similarity may NOT
accurately predict
evolutionary relationships!
CONVERGENT EVOLUTION:
Evolutionary change is not constant in rate and direction!
Cladistics
• Most systematists do NOT
base their phylogenetic
hypotheses on just similarities.
• Systematists use shared
derived characters … a.k.a
synapomorphies in
determining evolutionary
relationships. These are
similarities that arose from
a recent common ancestor.
• Similarity that arose before
the recent common ancestor
is called ancestral.
Making a Cladogram
• Characters should exist in easy to use character states.
(Ex) Hair vs. NO hair
• Character variation must be polarized - identified as
ancestral or derived. (Ex) Mammals: Hair is derived; lungs
is ancestral
Hair & Lungs
Lungs
Lungs
Making a Cladogram

Cladograms are important because
they utilize morphology and
biochemical data (DNA, rRNA).
It is now widely accepted that fungi
are more closely related to us than to
plants! Plants go back to Precambrian days.

Genomes compared are nuclear,
mitochondrial, and chloroplast
(in the case of the autotrophs).

Advent of the “DOMAIN”
CLADOGRAMS
When fossils for a recent common ancestor are
unavailable, systematists use an outgroup in order to
assign character polarity when creating a cladogram.
Outgroup
an organism
that is not part
of various
species in
question but is
closely related.
Fig. 23.6
CLADOGRAM
TAXON
NODE – represents
a common ancestor.
What does
this cladogram
tell us?
Fig. 23.1
FYI: Cladograms are sometimes
called “phylogenies” or “trees.”
CLADOGRAMS
The leopard and domestic
cat are more closely related
to each other than to the
wolf.
The leopard and domestic
cat represent sister taxa.
CLADOGRAMS
Could also be
"Taxon 3,
then Taxon 2.
It does not
matter.
What matters
is that they
branched off
at Node B.
Indicates that
scientists do
NOT yet
know who is
more closely
related ...
Taxon 4/5 ..
Taxon 4/6 or
Taxon 5/6.
Systematists
try to avoid
this when
making
cladograms.
WHICH CLADOGRAM IS DIFFERENT?
Step 1:
Which one looks
the most different?
Step 2:
Find a polytomy.
Step 3:
Count # of nodes
between taxons
to find an
inconsistency
a.k.a. … a taxon
further removed.
• Nodes can freely rotate making many different cladograms of a given set of organisms correct.
• In A, B, C, E, and F, species 6 shares a recent common ancestor with all species except 1
(outgroup). However, in D, 6 is not as closely related to 3 as in the other cladograms.
CLADOGRAMS

Clade – any branch of the evolutionary tree which is
separated from the rest of the tree by a single cut;
evolutionary units that refer to a common ancestor and
all of its descendants.
CLADOGRAMS
Synapomorphy
• A derived character shared by clade members (two or
more groups which originated in their last common
ancestor).
• Only synapomorphic character states can be used as
evidence that taxa are related!
• Phylogenetic trees are built by discovering groups
united by synapomorphies.
(EX) Feathers is unique to birds and defines all members
of the class Aves.
Outgroup
Mammals are a
clade, with hair
as a synapomorphy.
Figure 23.3
CLADOGRAMS
Plesiomorphy
An ancestral or primitive character; NOT
informative about phylogenetic relationships!
Symplesiomorphy
Character present in all the groups under
consideration
(EX) Vertebrae are found in zebras, cheetahs,
and orangutans, but the common ancestor in
which this trait first evolved is so distant that
the trait is shared by many other animals.
Therefore, possession of vertebrae sheds
no light on the phylogenetic relations of these
three species!
NOTE: Synapomorphy and
plesiomorphy are relative
concepts! Their status depends
on their position in the phylogeny.
A character is an synapomorphy
at one branch of the tree, but is a
plesiomorphy relative to all the
branches after that. For example, hair is a
mammalian feature (a synapomorphy of
mammals), but is primitive in squirrels (a
plesiomorphy). We can use presence of hair
as evidence for the existence of Mammalia,
but NOT for the existence of Sciuridae.
CLADOGRAMS
… a COMPLICATION!
Homoplasy
• Shared character
state that has NOT
been inherited from
a common ancestor
exhibiting that
character state.
• Can result from
convergent evolution
or from evolutionary
reversal.
Like gorillas &
humans, frogs
do not have a tail.
Figure 23.3
CLADOGRAMS

We must be careful if examining only morphological features …
4-chambered heart
4-chambered heart
The bird’s 4-chambered
heart must have
arose sometime after
parting from the lizards!
HOMOPLASY
Lizard-Bird Clade
CLADOGRAMS
Most cladograms are constructed based on the principle of
parsimony: Design a cladogram with the LEAST number of
changes necessary to come up with a tree … a.k.a. “Occam’s
Razor”
15%
15%
Total %
change
of 35%
15%
20%
5%
Tree 1: MORE likely
Fungi are
more
closely
related to
us than
to plants!
5%
25%
10%
Total %
change
of 50%
Tree 2: less likely
CLADOGRAMS
Short interspersed nuclear elements:
parasitic genes taken up by eukaryotes.
The 4 unique SINE genes outweigh
the loss of the talus bone. Therefore,
the hippo and whale are sister taxa!
The principle of parsimony ONLY
works if characters evolve at a
SLOW rate!
(Talus bone) - bone in
the foot that forms the
lower part of the ankle
joint
CLADOGRAMS
Which has the highest degree of parsimony?
A 7-nucleotide sequence compared amongst four species.
CLADOGRAMS
Which has the highest degree of parsimony?
1st Step:
For position 1, Species I has a different nucleotide.
CLADOGRAMS
Which has the highest degree of parsimony?
2nd Step:
For position 2, Species III has a different nucleotide.
CLADOGRAMS
Which has the highest degree of parsimony?
3rd Step:
For position 3, Species IV has a different nucleotide.
CLADOGRAMS
4th Step:
Which has the highest degree of parsimony?
For position 4, Species II has a different nucleotide.
So far all 3 cladograms have an equal chance of being the
most parsimonious!
CLADOGRAMS
5th Step:
Which has the highest degree of parsimony?
5
SLASHES
6
SLASHES
6
SLASHES
For position 5, we will use guanine (G) as the basal nucleotide ... Species III
and IV have a difference.
In the 1st cladogram, III and IV are sister clades. Therefore you just put 1
slash below.
CLADOGRAMS
6th Step:
Which has the highest degree of parsimony?
6
SLASHES
8
SLASHES
8
SLASHES
For position 6, we will use guanine (G) as the basal nucleotide ...
Species III and IV have a difference. In the 1st cladogram, III and IV are
sister clades. Therefore you just put 1 dark purple slash below.
CLADOGRAMS
Which has the highest degree of parsimony?
7th Step:
Most parsimony!
8
SLASHES
9
SLASHES
10
SLASHES
For position 7, we will use thymine (T) as the basal nucleotide ...
Species II and IV have a difference. In the 2nd cladogram, II and IV are
sister clades. Therefore, you just put 1 blue slash below.
CLADOGRAMS
Is this better or worse? More or less than 8 mutations? III and IV are
sister clades. 8 once again! So you do need at least a 7 nucleotide
sequence.
The longer the sequence the better to distinguish
between sister taxa!
Character states are polarized by reference to an
outgroup…
Figure 23.4
Species A and B independently evolved from thymine to cytosine in site 8.
Systematics and
Classification
 Monophyletic – a clade; contains a common
ancestor and all of its descendants.
 Paraphyletic – a monophyletic group that
excludes some of the descendents.
 Polyphyletic – lacks the most recent
common ancestor of all members of the group.
CLADOGRAMS
Monophyletic Paraphyletic
Polyphyletic
contains a common
ancestor and all of its
descendants.
does not contain the most
recent common ancestor
of all its members.
contains its most recent
common ancestor, but does not
contain all the descendents of
that ancestor.
CLADOGRAMS
Descendents
not included
Most recent
common ancestor
PROTISTS!
Most recent
common
ancestors
not included
CLADOGRAMS
Figure 23.5
CLADOGRAMS
Figure 23.5
CLADOGRAMS
Figure 23.5
CLADOGRAMS
How do
we make
them?
CLADOGRAMS
CLADOGRAMS
CLADOGRAMS
CLADOGRAMS
Only present in single taxa. So they are NOT of any use.
We need synapomorphies…
CLADOGRAMS
Earthworm
Snail
Flatworms
Jellyfish
Sponge
They share segmentation!
Fruitfly
Starfish
Segmented
body
Humans
Head
develops 1st
Anus develops 1st
Mesoderm
Bilateral
Symmetry Symmetry
Cells with flagella
CLADOGRAMS
Figure 23.2