Name _____________________________________ Blk ____ Date __________________________
Similarities and differences: Understanding
Homology and Analogy
In everyday life, people look like one another for different
reasons. Two sisters, for example, might look alike
because they both inherited brown eyes and black hair
from their father. On the other hand, two people
attending an Elvis impersonators' convention may look
alike because they are both wearing rhinestone studded suits and long sideburns. The similarity
between the sisters is inherited, but the similarity between the Elvis impersonators is not.
Biological similarity
It works the same way in biology. Some traits shared by two living things were inherited from their
ancestor, and some similarities evolved in other ways. These are called homologies and analogies.
Homology: traits inherited by two different organisms from a common ancestor
Analogy: similarity due to convergent evolution, not common ancestry
Fossils
Review the skulls & front leg fossils of ancestors of the our current horse. Source:
Equus
(modern horse)
Pilohippus
Merychippus
Mesohippus
http://www.iq.poquoson.org
Eohippus
(Dawn Horse)
1. Give two similarities between the series of skulls and one similarities for the set of front leg fossils
that might lead to the conclusion that these are all related species.
Skull Similarities
Front Leg Similarity
1.
1.
2.
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2. What is the biggest change in the skull and leg of the horse’s anatomy that occurred from the
dawn horse to the modern horse?
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Embryology
Source: http://www.starlarvae.org
Organisms that are closely
related may also have
physical similarities before
they are even born! Take a
look at the six different
embryos:
3. Hypothesize which embryo above forms each of the following organisms and what clues did you
for deciding:
Species
Human
Chicken
Rabbit
Tortoise
Salamander
Fish
Embryo
Clues
These are older, more developed
embryos from the same organisms,
in the same order.
4. Revisit your choices and
determine which embryo forms
each of the following organisms
and tell any clues that helped you.
Species
Human
Chicken
Rabbit
Tortoise
Salamander
Fish
Embryo
Clues
These are embryos at their most advanced
stage, shortly before birth.
5. Describe how the embryos changed for
each of these organisms from their earliest to
latest stages.
Species
Human
Chicken
Rabbit
Tortoise
Salamander
Fish
Anatomical Changes From Early to Late Stages
Comparative Anatomy – Homologous
Shown are images of the skeletal
structure of the front limbs of 6
animals: human, crocodile, whale, cat,
bird, and bat. Each animal has a similar
set of bones.
6. Color code each of the bones according
to this key:
HUMERS RED
CARPALS
YELLOW
ULNA
BLUE METCARPALS ORANGE
RADIUS GREEN PHALANGES PURPLE
7. For each animal, indicate what type of movement each limb is responsible for. Also, compare the
skeletal structure of each limb to the human arm. Relate the differences you see in form to the
differences in function.
Animal
Primary Functions
Human
Using tools, picking up and
holding objects
Whale
Comparison to Human Arm Comparison to Human Arm
in Form
in Function
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XXXXXXXXX
Whale has a much shorter The whale fin needs to be
and thicker humerus,
longer to help in movement
radius, and ulna. Much
through water. Thumbs are
longer metacarpals. Thumb not necessary as the fins are
has been shortened to a
not used for grasping.
stub.
Cat
Bat
Bird
Crocodile
Comparative Anatomy – Analogous
Shown are images of the structure of the
different wings of: moth, pterodactyl, bird, and
bat. Each animal has a similar use for their
wings. Compare the anatomy of each of the
wings.
8. What is the function of each of these
structures?
______________________________________
9. How are they different in structure? Give specific differences.
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Vestigial Structures - Compare the overall
body structure of the cave fish and the
minnow.
10. What is the biggest, most obvious
difference between the body structures of these two fish?
__________________________________________________________________________________
11. Assume the two fish came from the same original ancestor. Why might the cave fish have
evolved without eyesight?
__________________________________________________________________________________
12. What kind of sensory adaptation would you hypothesize the cave fish has to allow it to navigate
in a cave, including catching and eating food?
__________________________________________________________________________________
13. Listed vestigial structures found in humans. Hypothesize what its function may have been.
Structure
Possible function?
Wisdom teeth
Appendix
Muscles that moves the ear
Muscles that stand up body hair
Little toe
Tailbone
You have now studied three different types of relationships between organisms:
Homologous structures show individual variations on a common anatomical theme. These are seen
in organisms that are closely related. Typically same Structure, different Function.
14. Give an example of a homologous structure from this activity: __________________________
Analogous structures have very different anatomies but similar purposes. These are seen in
organisms that are not necessarily closely related, but live in similar environments and have similar
adaptations. Typically same Function, different Structure.
15. Give an example of an analogous structure from this activity: ___________________________
Vestigial structures are anatomical remnants that were important in the organism’s ancestors, but
are no longer used in the same way.
16. Give an example of a vestigial structure from this activity: ______________________________