3. Systematics - field of biology dealing with
diversity and evolutionary history of life
Includes Taxonomy: DINC
Description
Identification
Nomenclature
Classification
Goal:
– Determine Evolutionary History (Phylogeny) of Life
5. Identification
= associate an unknown with a known
How? One way:
Taxonomic Key, e.g.,
Tree
Leaves simple …….………………………… Species A
Leaves pinnate …….………..…..…..…… Species B
Herb
Flowers red …….…………………………… Species C
Flowers white …….…………………..…… Species D
6. Nomenclature
Naming, according to a formal system.
Binomial: Species are two names (Linnaeus):
E.g., Homo sapiens
Homo = genus name
sapiens = specific epithet
Homo sapiens = species name
11. Phylogenetic classification
• Based on known (inferred) evolutionary
history.
• Advantage:
– Classification reflects pattern of evolution
– Classification not ambiguous
17. Apomorphy (derived trait)
= a new, derived feature= a new, derived feature
E.g., for this evolutionary transformationE.g., for this evolutionary transformation
scales --------> feathersscales --------> feathers
(ancestral feature)(ancestral feature) (derived feature)(derived feature)
Presence of feathers is anPresence of feathers is an apomorphyapomorphy
for birds.for birds.
18. Taxa are grouped by apomorphies
Apomorphies are the result of evolution.
Taxa sharing apomorphies
underwent same evolutionary history
should be grouped together.
19. Principle of Parsimony
That cladogram (tree) having the fewest number
of “steps” (evolutionary changes) is the one
accepted.
Okham’s razor: the simplest explanation, with
fewest number of “ad hoc” hypotheses, is
accepted.
20. Other methods of phylogeny
reconstruction:
• Maximum Likelihood or Bayesian analysis
– Uses probabilities
– Advantage: can use evolutionary models.
21. apomorphies
(for Taxa B & C)
apomorphy
(for Taxon D)
apomorphy
(for Taxa B,C,D,E,F)
A B C D E F
TIME
Cladogram or Phylogenetic Tree
TAXA
22. Fig. 26-11
TAXA
Lancelet
(outgroup)
Lamprey
Salamander
Leopard
Turtle
TunaVertebral column
(backbone)
Hinged jaws
Four walking legs
Amniotic (shelled) egg
CHARACTERS
Hair
(a) Character table
Hair
Hinged jaws
Vertebral
column
Four walking legs
Amniotic egg
(b) Phylogenetic tree
Salamander
Leopard
Turtle
Lamprey
Tuna
Lancelet
(outgroup)
0
0 0
0
0
0
0 0
0
0
0 0
0 0 0 1
11
111
1
11
1
1
11
11
Sequentially group taxa by
shared derived character states (apomorphies)
27. Homoplasy (analogy)
• Similarity not due to common ancestry
• Reversal – loss of new (apomorphic) feature,
resembles ancestral (old) feature.
• Convergence (parallelism) – gain of new,
similar features independently.
30. Both examples of reversal within Tetrapods:
loss of a derived feature – forelimbs.
Leg-less lizards Snake
Example of convergence relative to one another!
Independently evolved.
snakes
leg-less
lizards
legged
lizards
**
*= loss of legs
gain of legs (Tetrapods)
33. Fig. 26-18
(b) Paralogous genes
(a) Orthologous genes
Ancestral gene
Paralogous genes
Ancestral species
Speciation with
divergence of gene
Gene duplication and divergence
Species A after many generations
Species A Species B
Species A
Orthologous genes
Orthology –
genes
homologous
Paralogy –
genes not
homologous
Gene Duplication
can occur!
34. Monophyletic Group
• a group consisting of:
– a common ancestor +
– all descendents of that common ancestor
35. monophyletic
group
A B C D E F
TIME
Cladogram or Phylogenetic Tree
TAXA
common ancestor
(of taxon A & taxa B-F)
common ancestor
(of taxon D, E, & F)
36. monophyletic
group
A B C D E F
TIME
Cladogram or Phylogenetic Tree
TAXA
common ancestor
(of taxon A & taxa B-F)
common ancestor
(of taxon D, E, & F)
37. monophyletic
group
A B C D E F
TIME
Cladogram or Phylogenetic Tree
TAXA
common ancestor
(of taxon A & taxa B-F)
common ancestor
(of taxon D, E, & F)
38. monophyletic
group
A B C D E F
TIME
Cladogram or Phylogenetic Tree
TAXA
common ancestor
(of taxon A & taxa B-F)
common ancestor
(of taxon D, E, & F)
39. monophyletic
group
A B C D E F
TIME
Cladogram or Phylogenetic Tree
TAXA
common ancestor
(of taxon A & taxa B-F)
common ancestor
(of taxon D, E, & F)
40. A B C D E F
TIME
speciation
Cladogram or Phylogenetic Tree
TAXA
41. A B C D E F
TIME
speciation
Cladogram or Phylogenetic Tree
TAXA
C B F E D A
Cladograms can be “flipped” at nodes, show same
relationships
43. Relationship
• = recency of common ancestry
i.e., taxa sharing a common ancestor
more recent in time are more closely related
than those sharing common ancestors more
distant in time.
51. A B C D E F
TIME
speciation
Cladogram or Phylogenetic Tree
TAXA
C B F E D A
Is “E” more closely related to “D” or to “F”?
Is “E” more closely related to “B” or to “A”?
Is “E” more closely related to “B” or to “C”?
52. A B C D E F
TIME
speciation
Cladogram or Phylogenetic Tree
TAXA
C B F E D A
Is “E” more closely related to “D” or to “F”?
Is “E” more closely related to “B” or to “A”?
Is “E” more closely related to “B” or to “C”?
Answers: F, B, neither (equally to “B” & “C”)
53. Paraphyletic group
• Consist of common ancestor but not all
descendents
• Paraphyletic groups are unnatural, distort
evolutionary history, and should not be
recognized.
65. We are human, but
we are also apes.
• We share unique human features.
• We also share features with other apes
(and with other animals, plants, fungi,
bacteria, etc.).
• Humans didn’t evolve from apes, humans
are apes.
66. All of life is interconnected
by descent.
A B C D E F
TIME
lineage
or clade
Cladogram or Phylogenetic Tree
TAXA
67. There are no “higher” or
“lower” species.
A B C D E F
TIME
lineage
or clade
Cladogram or Phylogenetic Tree
TAXA
68. Importance of systematics & evolution:
1) Foundation of biology - study of biodiversity
2) Basis for classification of life
3) Gives insight into biological processes:
speciation processes
adaptation to environment
4) Can be aesthetically/intellectually pleasing!
