Transcript 6.9 Analogous and Vestigial Structures

Analogous and Vestigial Structures
Catalyst
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Humans and cows both have hearts with four
chambers. What type of structure is this, and what
does it tell us about how humans and cows
evolved?
What are two things all animal embryos have in
common? What does this tell us about how
animals evolved?
Write in complete sentences!
Don’t talk during the Catalyst!
Objectives
By the end of today, all SWBAT…
 Explain how analogous structures
support the theory of evolution
 Explain how vestigial structures
support the theory of evolution
Catalyst Review

Humans and cows both have hearts with four
chambers. What type of structure is this, and
what does it tell us about how humans and
cows evolved?
 It is a homologous structure.
 This shows that humans and cows evolved
from a common ancestor with a fourchambered heart.
Catalyst Review
What are two things all animal embryos have
in common? What does this tell us about how
animals evolved?
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All animal embryos have gill slits and tails.
This is evidence that all animals evolved from the
same common ancestor.
Comparative Anatomy
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Scientists can
compare the
anatomy of
different organisms
to figure out how
closely they are
related.
Anatomy
structure
= body
Analogous Structures
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Analogous structure: parts of different species that have
the same function, but EVOLVED SEPARATELY
Key Point #1:
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Analogous structures show that unrelated* species will evolve
similar adaptations in response to similar environmental
pressures
Natural selection selects for (keeps around) mutations that
increase fitness in the specific environment.
If organisms they live in similar environments, they will
evolve similar structures.
Insect, bird, and bat wings evolved completely separately.
Unrelated organisms will evolve similar adaptations in
response to similar environmental pressures!
No recent common ancestor!!!
Seals and penguins both have streamlined bodies, and store
fat to keep them warm in the cold water. Unrelated
organisms will evolve similar adaptations in response to
similar environmental pressures!
Vestigial Structures
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Vestigial structure: part of an organism that is no
longer used for anything
Key Point #2:
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Vestigial structures show that a species used to live in a
different environment.
Organism moved into a new environment, where the
vestigial structure decreases fitness
No longer needed, waste of energy
 Risk of disease

Letter “c” = hind legs of a baleen whale skeleton
Vestigial = no longer used!!!
Blind salamanders have eye sockets!?!?
Guided Practice – Notes Reflection

How do analogous structures provide evidence for
evolution?
 Analogous
structures show that unrelated* organisms
will evolve similar adaptations in response to similar
environmental pressures
If you can’t find the answer…
ADD IT!!!
Guided Practice – Notes Reflection

How do vestigial structures provide evidence for
evolution?
 Vestigial
structures show that the species used to live in
a different environment
 Organism moved into a new environment where the
vestigial structure decreased fitness… so it started to
degrade
If you can’t find the answer…
ADD IT!!!
Study!
Guided practice will cover
yesterday’s lesson (homologous
structures) as well as today’s
(analogous and vestigial structures).
 Take three minutes to study your
notes from yesterday and refresh
your memory before we proceed.

Guided Practice (GP)
Are these structures…
(A) Homologous, (B) Vestigial, (C) Analogous?

Human embryos and cat embryos both have gill
slits.
HOMOLOGOUS
Guided Practice (GP)
Are these structures…
(A) Homologous, (B) Vestigial, (C) Analogous?

Birds and insects both have wings, but they
developed in completely different ways.
ANALOGOUS
Guided Practice (GP)
Is this structure…
(A) Homologous, (B) Vestigial, (C) Analogous?
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Snakes don’t have legs, but they do have hip and
leg bones.
VESTIGIAL
Guided Practice (GP)
Is this structure…
(A) Homologous, (B) Vestigial, (C) Analogous?
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The human appendix – a small organ next to the
intestines – doesn’t seem to do anything at all.
VESTIGIAL
Guided Practice (GP)
Are these structures…
(A) Homologous, (B) Vestigial, (C) Analogous?
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Cat embryos and human embryos both have tails.
HOMOLOGOUS
Guided Practice (GP)
Are these structures…
(A) Homologous, (B) Vestigial, (C) Analogous?
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Dolphins and sharks both have fins, but they
evolved completely differently.
ANALOGOUS
Guided Practice (GP)
Are these structures…
(A) Homologous, (B) Vestigial, (C) Analogous?
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Alligators and bats have the same bone structure in
their forelimbs (front legs for alligators, wings for
bats).
HOMOLOGOUS
Guided Practice (GP)
Is this structure…
(A) Homologous, (B) Vestigial, (C) Analogous?
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Humans have wisdom teeth (third molars), even
though they are not needed to chew up food.
VESTIGIAL
Guided Practice (GP)
Are these structures…
(A) Homologous, (B) Vestigial, (C) Analogous?

Humans and squids both have eyes, but they
evolved in completely different ways.
ANALOGOUS
Independent Practice (IP)
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Get an early start on the homework.
Key Point Wrap-Up
Key Point #1: Analogous structures show
that unrelated* species will evolve similar
adaptations in response to similar
environmental pressures
 Key Point #2: Vestigial structures show that
a species used to live in a different
environment.

 Organism
moved into a new environment, where
the vestigial structure decreases fitness
Exit Question: Choose one option
A
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What is one thing that
human embryos and
dolphins embryos both
have in common?
What kind of structure is
this?
How do these structures
provide evidence for
evolution?
B
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Write in complete sentences!
Dogs and alligators both
have long snouts that
allow their jaws to open
wide. However, they
evolved in completely
different ways.
What kind of structure is
this?
How do these structures
provide evidence for
evolution?