a concept of entomology and zoology

1. HOMOLOGY
( Methods in identification of
homology species concepts )
Presented by,
Guru P. N.
Ph. D. 015/39
Dept. of Agril. Entomology,
PGI, MPKV, Rahuri.

2. Species Concepts
1. The Typological Species Concept
(TSC, Linnaeus)
A group of individuals that differ
from other groups by possessing
constant diagnostic characters.

3. 2. The Biological Species Concept
(BSC, Dobzhansky, Mayr)
Mayr (1940):
species are groups of actually or
potentially interbreeding natural
populations that are reproductively
isolated from other such groups.
Dobzhansky (1937):
species are the largest and most
inclusive reproductive community of
sexual and cross-fertilizing
individuals that share a common
gene pool.

4. 3. The Evolutionary Species Concept
(ESC, Simpson, 1951)
An evolutionary species is a
lineage evolving separately
from others with its own
unitary evolutionary role and
tendencies.

5. 4. The Phylogenetic Species Concept
(PSC, Cracraft, 1983)
The smallest diagnosable
monophyletic group of populations
within which there is a parental
pattern of ancestry and descent.

6. Homology species concept

7. Universal ancestor
Evidence of common descent
1. Evidence from comparative physiology and biochemistry
2. Evidence from comparative anatomy
1. Homologous structures and divergent (adaptive)
evolution
3. Evidence from paleontology
4. Evidence from geographical distribution
5. Evidence from selection
6. Evidence from speciation
7. Evidence from computation and mathematical iteration

8.  Comparative study reveals that they are based upon a common
prototype or ground plan, which varies with the organism’s
particular environment
 The interpretation of anatomy requires an understanding of
homologous versus analogous structures:
COMPARATIVE ANATOMY
wingsVertebrate forearms

10. Homology
• Similarity resulting from common ancestry.
e.g., the forelimb bones of a bird, bat, and cat.

11. 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.
Comparison of insect and bird
wings to show their analogy

12. a. Homology
Two species bearing the same phenotype
caused by common ancestry for the same
genotype.
c. Convergence
Two species with the same phenotype whose
common ancestor is very far in the distant past
b. Parallelism
Two species with the same phenotype descended
from a common ancestor with a different phenotype
and genotype
Species
1
Species
2
Phenotype a
Phenotype b
Species
1
Species
2
Species
1
Species
2
Ancestor
phenotype a
Ancestor
phenotype b
Phenotype c

13.  Homology is assessed regardless of shape or function. Only
morphological equivalence in terms of relative position, structure,
and connections with nerves and blood vessels counts.
HOMOLOGY FORMS
 Phylogenetic or evolutionary homology: provided the organisms
are members of different species.
 commonly used in systematics and phylogenetics
 Iterative homology, i.e. homology between parts of the same
organism, like the homology between foliage leaves and petals on
flowering plants.
 (homonomy, or serial homology, if the structures are arranged along
the main body axis)

14. 1. The Idealistic Homology Concept : non-historic causes
• Two characters are thought to be homologous because they are
built according to the same plan or archetype.
2. The Historical Homology Concept
• Relationship between those parts of different organisms that
correspond to an equivalent organ in a common ancestor.
3. The Biological Homology Concept (Roth, 1984)
• “Homology is resemblance caused by a continuity of information”
• Roth: "sharing of pathways of development, ( . . . ) controlled by
genealogically related genes"
DIFFERENT HOMOLOGY CONCEPTS

15. Vertebrate Limbs & Common Ancestor

16. Can Genes be Homologous?

17. Which limb is NOT homologous in each set? Why?
B
Bird
B
Whale
Grasshopper
Lizard
Human
A Human
LizardOctopus
Human
LizardLizard
Human
LizardOctopus Lizard
Human
Octopus Lizard
A Human
Octopus Lizard
A Human
Octopus Lizard

18. 1. Are the wings of a bat (mammal) and the wings of
a robin (bird) homologous?
No
(they do not share a common
ancestor with wings)

19. 2. Fins of a shark (fish) and the fins of a
dolphin mammal?
No
(they do not share a common
ancestor with fins)

20. 3. The limbs of an eagle and the limbs of a
penguin?
Yes
(both are birds that have adapted
different uses for their wings)

21. 4. Wings of a dragon fly and the wings of a
butterfly?
Yes
(both are insects that evolved from
insects with wings)

22. 5. Are all of these different leaves Homologous?
Yes
(all are types of modified leaves
from different plants)

25. Thank you
all….
Presented by,
Guru P. N.
Ph.D. 015/39