Name:________________________________Date:_______Period:________
Anatomical Evidence For Evolution
3.4.2.2
Evolution is the theory that species change over time. This change is caused
by natural selection. As you recall, natural selection allows certain organisms to
reproduce while not allowing others to reproduce. Those organisms most fit for
their environment survive and reproduce, while less fit members do not reproduce
as well. This process is known as evolution.
REMEMBER THIS!!!
Evolution is a theory that states that species change over time in response to
natural selection.
There is evidence that shows evolutionary relationships between organisms.
Some organisms are more alike than others. For instance a dog is more closely
related to a wolf than it is to a fish. Sometimes, biologists use fossils of organisms
that lived in the past to determine how closely certain organisms are related. They
also use evidence in the organisms that are alive today. Homologous structures,
analogous structures and vestigial structures all are used by biologist to study
which species are more closely related to each other.
Homologous structures have similar appearances, but function differently
in different organisms. For example, your arm is made of one bone between your
shoulder and elbow, two bones between your elbow and wrist, and many bones in
your hands in fingers. Other animals, like birds, turtles, frogs, and bats have the
same appearance in their forearms (one bone, two bones, and many bones from the
shoulder down). In all of these organisms the job of the forearm is a little bit
different. Yet they look the same. Structures that show similar design are
called homologous structures.
Since genes produce the structures in organisms, biologists assume that
organisms with homologous structures share similar genes. The more similar
the genes are in different organisms, the more closely related they are.
Birds, turtles, frogs, humans, and bats all have a similar bone structure in their
forearm. Therefore, we share similar genes with birds, turtles, frogs and bats
because our forearms are homologous to theirs. This makes us more closely
related to them than to other organisms, like a jellyfish, that doesn’t have similar
homologous structures.
REMEMBER THIS!!!
Animals that have homologous structures are more closely related than animals
that do not have homologous structures. Homologous structures between
animals indicate that they have some DNA in common; therefore they are
more closely related.
Question 1. Explain why organisms that have homologous structures are more
closely related than organisms that do not have homologous structures.
Analogous structures are structures that do the same job, but do not
come from similar genes. For example, the wing of a butterfly and the wing of
a bat are analogous structures. They both do the same job they help the organism
to fly. However, the wings of a bat have bones inside them. The wings of the
butterfly do not have bones. Therefore, the genes that produced the wings in
bats and butterflies are not the same. As a result, butterflies and bats are not
very closely related.
REMEMBER THIS!!!
Analogous structures do not indicate a relationship. They have no common
DNA.
Question 2. Analogous structures perform the same function so why don’t
analogous structures indicate a degree of kinship?
Vestigial structures are structures that have no function in an organism.
They are there because the organisms still has some genes that produced
structures that its ancestors needed. For example, snakes are believed to have
evolved from lizards that found safety by burrowing. Their legs became less and
less important for survival, so natural selection allowed populations of legless
lizards (snakes) to survive and reproduce. Some snakes still have a pelvis, the bone
that attaches the legs to the body. Snakes have no need for a pelvis, but they still
have the genes that produce it. It is an example of a vestigial structure. In
humans, the appendix is an example of a vestigial structure.
REMEMBER THIS!!!
Vestigial structures are present but not needed and usually do not function.
They may indicate a degree of kinship.
Question 3. How can a structure that has no function demonstrate a relationship
between two animals?
TEST YOURSELF
Matching
____ 1. Evolution
a. structures that have no functions
in organisms
____ 2. homologous structures
b. structures that come from similar
genes
____ 3. analogous structures
c. structures that do not come from
similar genes, but do the same
job
____ 4. vestigial structures
d. the theory that species change
over time
____ 5. bat wings and butterfly wings
e. an example of a homologous
structure
____ 6. a pelvis bone in a snake
f. an example of an analogous
structure
____ 7. bat wings and human arms
g. an example of a vestigial structure
Fill in the Blanks – Words may be used more than once.
Analogous
Evolution
Bats
Lizards
homologous
genes
butterflies
vestigial
turtles
snakes
1. The more _______________ organisms have in common, the more related they
are.
2. In the past, organisms changed as their environment changed according to the
theory of ____________________________.
3. To help understand which organisms are more closely related, biologist study
_________________, ____________________, and _________________
structures.
4. __________ and _________________ both have wings, but the wings are
produced by different genes. These structures are called
_____________________ structures.
5. ______________ and _____________ have similar bone structure in their
forearms, produced by similar genes. These structures are called
____________________
structures.
6. ______________, which has a pelvis bone they don’t need, are thought to be
related closely related to __________________.
True or False
____ 1.
Evidence for evolution only comes from fossils.
____ 2.
Evidence for evolution can be found in living organisms.
____ 3.
Bird wings and butterfly wings are homologous structures.
____ 4.
Bird wings and butterfly wings are analogous structures.
____ 5.
Bird wings and turtle forearms are homologous structures.
____ 6.
Bird wings and turtle forearms are analogous structures.
____ 7.
Birds are more closely related to butterflies than to turtles.
____ 8.
Birds are more closely related to turtles than to butterflies.
____ 9.
Homologous structures show that organisms have similar genes.
____ 10. Analogous structures show that organisms have similar genes.
____ 11. Vestigial structures show that organisms have similar genes
____ 12. Some snakes have a pelvis bone because they need it.
____ 13. Some snakes have a pelvis bone because their ancestors had one.
____ 14. The pelvis bone in snakes is called a vestigial structure.
____ 15. The pelvis bone in snakes shows that snakes may be related to lizards.
Answer the Following
1. Explain the theory of evolution?
2. What evidence from the past supports the theory of evolution?
3. What is a homologous structure? Give an example.
4. What is an analogous structure? Give an example.
5. What is a vestigial structure? Give an example.