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Interpreting Cladograms Notes
INTERPRETING CLADOGRAMS
BIG IDEA:
PHYLOGENIES DEPICT ANCESTOR AND DESCENDENT
RELATIONSHIPS AMONG ORGANISMS BASED ON
HOMOLOGY
THESE EVOLUTIONARY RELATIONSHIPS ARE
REPRESENTED BY DIAGRAMS CALLED CLADOGRAMS
(BRANCHING DIAGRAMS THAT ORGANIZE
RELATIONSHIPS)
Reading Cladograms
 Read like a family tree: show
patterns of shared ancestry
between lineages.
• When an ancestral lineage
splits: speciation is indicated
due to the “arrival” of some
new trait.
Each lineage has unique traits to itself
alone and traits that are shared with
other lineages.
each lineage has ancestors that are unique
to that lineage and ancestors that are
shared with other lineages — common
ancestors.
Quick Question #1
 What is our definition of a clade?
 (look back to zoology notes #1 if
you cannot remember)
 A group that includes a common
ancestor and all the descendants
(living and extinct) of that
ancestor.
Reading Cladogram: Identifying Clades
 Using a cladogram, it is easy to tell if a group of
lineages forms a clade.
 Imagine clipping a single
branch off the phylogeny
 all of the organisms on
that pruned branch
make up a clade
 So everything in the
pink circle is a clade
(common ancestor and
all descendants)
Quick Question #2
 Looking at the image to
the right:
 Is the green box a clade?
 The blue?
 The pink?
 The orange?
Reading Cladograms: Clades
 Clades are nested within one another
 they form a nested hierarchy.
 A clade may include many thousands of species or
just a few.
Interpreting Cladograms
 it's easy to misinterpret cladograms as implying that
some organisms are more "advanced" than others
 however, cladograms don't imply this at all.
 when reading a cladogram, it is important to keep
three things in mind
(mis)Interpreting Cladograms: One
 Evolution produces a pattern of relationships among
lineages that is tree-like, not ladder-like.
(mis)Interpreting Cladograms: Two
 Just because we tend to read phylogenies from left to
right, there is no correlation with level of
"advancement."
(mis)Interpreting Cladograms: Three
 For any speciation event on a phylogeny, the choice
of which lineage goes to the right and which goes to
the left is arbitrary. The following phylogenies are
equivalent:
Interpreting Phylogenies: Human Example
 The points described above cause the most problems when it comes to
human evolution.
 It is important to remember that:


Humans did not evolve from
chimpanzees. Humans and
chimpanzees are evolutionary cousins
and share a recent common ancestor
that was neither chimpanzee nor human.
Humans are not "higher" or "more evolved" than other living
lineages. Since our lineages split, humans and chimpanzees have
each evolved traits unique to their own lineages.
Quick Question #3
 What is this
called?
 What do you
think the red
lines
represent?

Creation of Cladograms
 Given a set of observations, phylogenetic analysis
seeks to find the simplest branching relationships
between organisms to depict their evolution.
 Heritable traits possessed by organisms, characters,
are used to compare the organisms being studied.
• Characters can be
compared across
organisms
• physical traits
• genetic sequences
• behavioral traits.
BUT HOW DO WE
CONSTRUCT A CLADOGRAM?
3 Alternative, mutually
exclusive Cladograms
How Do We Choose
Between Them?
INGROUP ORGANISMS
Characters
PP
RD
PC
Fur/Mane
No
Yes
Yes
Yes
Toes/Foot
Many Toes
One Hoof
One Hoof
One Hoof
Wings
No
No
Yes
Yes
Horn
No
No
(Not an Ancestor, but a
Eyes
Yes
Stand-in to represent
the Yes
TailAncestral Condition)
Yes
Yes
No
Yes
Yes
Yes
Yes
Yes
Mouth
Yes
Yes
Yes
Outgroup
Primitive (ancestral) State
Yes
Derived States
INGROUP ORGANISMS
Characters
Fur/Mane
Toes/Foot
Wings
Horn
Eyes
Tail
Mouth
Outgroup
PP
RD
PC
No
Many Toes
No
No
Yes
Yes
Yes
Yes
One Hoof
No
No
Yes
Yes
Yes
Yes
One Hoof
Yes
No
Yes
Yes
Yes
Yes
One Hoof
Yes
Yes
Yes
Yes
Yes
3 Steps (evolutionary
transitions from
ancestral  derived)
to explain this tree
Derived character states found
in only one organism separate
them from other organisms
Horn
Wings
Fur/Mane
One Hoof
Ancestral characters
shared by all taxa link
organisms together
Eyes
Tail
Mouth
Taxa
Characters
Fur/Mane
Toes/Foot
Wings
Outgroup
RD
PP
PC
No
Many Toes
No
Yes
One Hoof
Yes
Yes
One Hoof
No
Yes
One Hoof
Yes
Loss of Wings
4 Steps (with wings
developing
convergently)
OR
4 Steps (with wings
developing in ancestral
pony, and lost in PP)
Wings
Wings
Fur/Mane
One Hoof
Wings
Taxa
Characters
Fur/Mane
Toes/Foot
Wings
Outgroup
PC
PP
RD
No
Many Toes
No
Yes
One Hoof
Yes
Yes
One Hoof
No
Yes
One Hoof
Yes
Loss of Wings
4 Steps (with wings
developing
convergently)
OR
4 Steps (with wings
developing in ancestral
pony, and lost in PP)
Wings
Wings
Fur/Mane
One Hoof
Wings
3 Steps
The preferred cladogram is
the simplest! (Least
number of assumptions)
So, which cladogram is
the best description of
the evolution of these
little ponies?
4 Steps
4 Steps
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