Analogous and Vestigial Structures
Catalyst
Cougars eat Bucaneers, which have decreased in
population over the past few years. What is the
environmental pressure?
Humans and cows both have hearts with four chambers.
1.
2.


3.
Write in complete sentences!
Don’t talk during the Catalyst!
What type of structure is this?
Describe what it tells 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?
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

Cougars eat Bucaneers, which have decreased
in population over the past few years. What is
the environmental pressure?
 The
environmental pressure is the decrease in
population of the Bucaneers.
 WHY?
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?
 Human and cow hearts are homologous
structures.
 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?



All animal embryos have gill slits and tails.
This is evidence that all animals evolved from the
same common ancestor.
Homework Review
1.
2.
3.
4.
What are homologous structures? Provide two
examples of homologous structures.
What is an embryo?
What is a common ancestor? Give an example.
All animal embryos start off looking very
_______________. For example, they all have
_______________ and _______________. These
traits are examples of _______________
structures.
Homework Review
5.
6.
Lions and tigers have similarly structured tails.
What type of structures are these? EXPLAIN how
these structures support the theory of evolution.
(Hint: use the phrases “evolve” and “common
ancestor”!)
How can we use the appearance of cat and horse
embryos to support the theory of evolution? (Hint:
use the phrases “evolve” and “common ancestor”!)
Comparative Anatomy

Scientists can
compare the
anatomy of
different organisms
to figure out how
closely they are
related.
Anatomy
structure
= body
Analogous Structures


Analogous structure: Parts of different species that have
the same function, but EVOLVED SEPARATELY
Key Point #1: 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



Vestigial structure: Part of an organism that is no
longer used for anything
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
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!?!?
So, what about me?
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!
This 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?

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?

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?

Cat embryos and human embryos both have tails.
HOMOLOGOUS
Guided Practice (GP)
Are these structures…
(A) Homologous, (B) Vestigial, (C) Analogous?

Dolphins and sharks both have fins, but they
evolved completely differently.
ANALOGOUS
Guided Practice (GP)
Are these structures…
(A) Homologous, (B) Vestigial, (C) Analogous?

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?

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)

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
All humans have a tail bone,
but we don’t have tails.
 What type of structure is
this?
 EXPLAIN how this
structure provides
evidence for evolution.
B
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 type of structure is
this?
 EXPLAIN how these
structures provide
evidence for evolution.