1. AIM: Why are organisms classified
into groups?
Warm – up: Complete Exercise 3 in Lab

2. Necessary Terms
Taxonomy is the classification of organisms. Most
biologists feel that classification should
be based upon phylogeny.
Phylogeny is the ancestry of organisms- how
organisms are related by evolution
Systematics is the study of phylogeny.
Cladistics is a means of understanding the
phylogeny of organisms.

3. Phylogeny and Biochemistry
• Phylogeny of many
groups has been
studied by
comparing structures
of proteins or other
biochemicals (DNA,
RNA)
What about mutations?

4. Molecular Clocks
• Estimate time of
divergence by
comparing numbers
of neutral mutations
in DNA, which tend
to accumulate in the
DNA of a lineage at a
fairly constant rate.
• 70,000 years ago,
Euro – Japanese split
• 140,000 African –
EuroJapanese split
• 5 mya – human –
chimps split

5. Biochemistry and
Common Ancestry
• All use DNA (or RNA) as genetic material
• All use same universal genetic code
• All use same 20 amino acids in building
proteins
• All use left, not right handed amino acids)
What does this information tell us?

6. Cladistics and Taxonomy

7. Classification in Biology

8. Classification in Biology
Arranging living organisms into groups

9. Classification in Biology
Arranging living organisms into groups

10. Classification in Biology
Arranging living organisms into groups
WHY BOTHER?

11. Classification in Biology
Arranging living organisms into groups
WHY BOTHER?
1. Species Identification: Easier to find out to which
species an organism belong to if everything is
organized

12. Classification in Biology
Arranging living organisms into groups
WHY BOTHER?
1. Species Identification: Easier to find out to which
species an organism belong to if everything is
organized
2. Predictive Value: If several members of a group have
a particular characteristic, another species in this
group may also have this characteristic

13. Classification in Biology
Arranging living organisms into groups
WHY BOTHER?
1. Species Identification: Easier to find out to which
species an organism belong to if everything is
organized
2. Predictive Value: If several members of a group have
a particular characteristic, another species in this
group may also have this characteristic
3. Evolutionary Links: Species in the same group
probably share characterstics because they have
evolved from a common ancestor

14. Hierarchical
classification
Carolus Linnaeus
Binomial nomenclature

15. Seven basic categories of biological classification
More categories are added to recognize similarities among groups of taxa
within these levels, for example superfamilies, etc.
Kingdom
Phylum
Class
Order
Family
Genus
Species

17. Kingdom

18. Kingdom
Phylum

19. Kingdom
Phylum
Class

20. Kingdom
Phylum
Class
Order

21. Kingdom
Phylum
Class
Order
Family

22. Kingdom
Phylum
Class
Order
Family
Genus

23. Kingdom
Phylum
Class
Order
Family
Genus
Species

24. Classification of Humans

25. Classification of Humans
Kingdom (Animalia)

26. Classification of Humans
Kingdom (Animalia)
Phylum (Chordata)

27. Classification of Humans
Kingdom (Animalia)
Phylum (Chordata)
Class (Mammalia)

28. Classification of Humans
Kingdom (Animalia)
Phylum (Chordata)
Class (Mammalia)
Order (Primates)

29. Classification of Humans
Kingdom (Animalia)
Phylum (Chordata)
Class (Mammalia)
Order (Primates)
Family (Hominidae)

30. Classification of Humans
Kingdom (Animalia)
Phylum (Chordata)
Class (Mammalia)
Order (Primates)
Family (Hominidae)
Genus (Homo)

31. Classification of Humans
Kingdom (Animalia)
Phylum (Chordata)
Class (Mammalia)
Order (Primates)
Family (Hominidae)
Genus (Homo)
Species (Homo sapiens)

32. Artificial vs. Natural Classification
• Natural Classification: matches
evolutionary origins of the species in the
group
• Artificial classification: Help with species
identification but have no other value…
ex. Insects, birds, bats are put in the same
group. WHY?

33. Convergent evolution and analogous structures:
Not all similarity represents common ancestry!
The Ocotillo (SW U.S.A) and Allauidia (Madagascar) are not closely related.
Resemblance due to independent adaptations to similar environmental pressures.

34. Organisms with homologous
structures should be classified in
the same group because they
have a common ancestry, even if
they look different!

35. Homology vs. Analogy
• Homology refers to having a trait in common
because it has been inherited from a common
ancestor.
– CLADOGRAMS BASED ON HOMOLOGIES
• Species can also evolve the same traits
independently. Independent evolution of the same
characteristic is called convergent evolution and
those traits are called analagous.

36. Cladograms and Classification
Classification of many groups has been re-examined using
cladograms. In many cases, cladograms have confirmed
existing classifications. Not surprising since both traditional
classification and cladistics attempt to reflect phylogeny.
Cladograms can be difficult to reconcile with traditional
classifications, because the nodes can occur at any point. It can
therefore seem rather arbitrary how the hierarchy of taxa is
fitted to the clades. In some cases, cladistics suggests radically
different phylogenies. The strength of cladistics is that the
comparisons between organisms are objective, based on
molecular differences. The weakness is that molecular
differences are analyzed on the basis of probabilities.
Occasionally, improbable events occur makine the analysis
wrong. Therefore, cladistics should not be treated as infallible.
However, it can stimulate a reinterpretation of the data on
which traditional classifications have been based.

38. Cladogram: A phylogenetic
diagram that classifies
organisms according to shared

39. Cladogram: A phylogenetic
diagram that classifies
organisms according to shared
Clade: Group of organisms
that evolved from a common
ancestor (the ancestor plus
all its descendants)

40. Cladogram: A phylogenetic
diagram that classifies
organisms according to shared
Clade: Group of organisms
that evolved from a common
ancestor (the ancestor plus
all its descendants)
Cladistics: method of classification
of living organisms based on
construction and analysis of
cladograms

41. Connection
between
classification

42. Constructing a Cladogram

43. Constructing a Cladogram
Ancestral (=homologous) trait: A trait shared due to common ancestry

44. Constructing a Cladogram
Ancestral (=homologous) trait: A trait shared due to common ancestry
Derived trait: A trait that differs from a common ancestor

46. Cats are more similar to dogs than they are to frogs,
because they share a more recent common ancestor with
dogs

47. An outgroup is used to decide which characteristics are ancestral
Ingroup Outgroup

48. Procedure 1: Classifying Doodlebirds
?

50. Why are legs,
beak and crest
not useful in the
analysis?

51. (outgroup)
Web toes,
Three tails

52. TAXA Petal no. Leaf Seed shape
A 5 compound flat
B 4 compound round
C 4 simple round
D 5 compound round
Outgroup 4 simple round

54. A B C D
A 1 (compound) 0 2 (compound, 5)
B 0 1 (compound)
C 0
D