1. Evolutionary Biology: Phylogeny and
Cladistics

2. History
 Taxonomists have sought to construct a system that
would reflect evolutionary relationships.
 Use morphology to recognize and construct species

3. History
 Grande (2004)
 Proposes that we view morphology and morphological
variations in three ways
 Taxonomic
 Ontogenic
 Individual
 Ability to interbreed
 Biological species concept  Evolutionary species concept

4. Species Concept
 Morphological Species
 Generally used morphological criteria because this is how
most individuals have been compared.
 Biological Species
 Sexually interbreeding or potentially interbreeding group
of individuals normally separated from other species by
the absence of genetic exchange.
 Evolutionary Species
 species as an evolutionary entity.

5. Phylogeny
 Species evolve from existing species.
 Classification of species
 Homology
 2 species bearing the same phenotype caused by common
ancestry for the same genotype.
 Parallelism
 2 species with the same phenotype descended from a common
ancestor w/ different phenotype and genotype
 Convergence
 2 species with the same phenotype whose common ancestor is
very far in the distant past.

6. What is Cladistics?
 Method of hypothesizing evolutionary relationships
among organisms.
 Based upon the analysis of traits shared by
organisms.
 Cladogram: represents evolutionary relationships.
 Willi Hennig
 1950
 German zoologist

8. Assumptions of Cladistics
 The Characteristics of organisms change over time.
 All organisms are related by a descent from a
common ancestor
 There is a bifurcating or branching pattern of lineage
and splitting.

9. The Principle of Parsimony
 The principle of parsimony reasons that given
several solutions to a problem, the simplest one
should be accepted.
 The principle of parsimony does not:
 Provide absolute truth
 Necessarily reveal the true phylogeny
 The principle of parsimony does:
 Reduce conjecture
 Indicates those cladistic groupings best supported by the
available data

10. Understanding Cladogram
 The root of Cladogram represents the ancestral
lineage and the tips the descendants.
 Branching points in the cladograms are called nodes
and represents speciation events.
 Part of each lineage’s history is unique to it alone.
 Each lineage has ancestors that are unique and
ancestors that are shared with other lineages.
A B C D E F
TIME
speciation
Cladogram or Phylogenetic Tree
TAXA

11. Understanding Cladograms
 Clade: a group comprising an ancestral lineage and
all its descendant lineages.

12. Characters
 Inheritable feature of an organism.
 Physical characteristics (morphology)
 Genetic sequences
 Behavioral traits

13. Characters
 Homologous characters
 A character possessed by
two or more organisms due
to their sharing of a
common ancestor.

14. Characters
 Homoplasy
 Similar characters in different taxa inferred to have arisen
through convergent evolution, not a common ancestor.
 No use in cladistics

16. euphorb
spines
cactus
spines

17.  Plesiomorphy
 Considered to be ancestral or less derived
 Apomorphy
 Features considered to be derived from an ancestral
clade
 Synapomorphy
 An apomorphic feature that defines a clade.

18. Monophyletic group
 A group consisting of:
 A common ancestor
 All descendants of that common ancestor

24. Paraphyletic group
 A monophyletic grouping that certain descendent tax
have been removed from due to their possession of
additional synapomorphic characters.

25. Constructing a Cladogram
 Outgroup Method
 Works by identifying tow groups of taxa
 Ingroup: group being studies
 Outgroup: for the establishment of plesomorphic and
apomorphic character states in the ingroup
 The outgroup should comprise taxa closely related to the
ingroup so homologous characters can be established

26. Character states and Character Matrix
notochord vertebrae jaws skull lung enamel 4 true limbs
Outgroup 0 0 0 0 0 0 0
Tunicate 1 0 0 0 0 0 0
lamprey 1 1 0 1 0 0 0
Cladoselache 1 1 1 1 0 0 0
trout 1 1 1 1 1 0 0
lungfish 1 1 1 1 1 1 0
present 1
absent 0