Evolutionary
Evidence
Part 3: Anatomical Homology
Bellringer
• In your science journal, write
and respond to the following
question:
–Describe how the forelimbs of
vertebrates, illustrate homologous
structures. Provide examples.
Objectives:
• I can define and compare vestigial, homologous, and
analogous structures.
• I can examine and describe homologous and analogous
structures.
• I can analyze vestigial structures between species and
determine the likelihood of common ancestry.
• I can analyze homologous structures between species
and determine the likelihood of common ancestry.
• I can analyze analogous structures between species
and determine the likelihood of common ancestry.
What are the different types of evidence used
to support the evolutionary theory?
There are several places we
can see indirect evidence of
evolution/evolutionary
relationships:
 fossils,
 biogeography
 similarities in
anatomy,
 biochemistry/DNA,
 and embryology.
One form of evidence in the unity of life…..
Anatomical evidence
What are homologous structures? What
evidence do they provide?
Science sees structural similarities as evidence that
organisms evolved from a common ancestor.
Crocodile
forelimb
Bird
wing
Whale
forelimb
Homologous
parts are similar
in structure, but
may be very
different in
specific function.
Structural features with a common evolutionary origin
are called homologous structures.
What are analogous structures? What
evidence do they provide?
The body parts of organisms that do not have a common
evolutionary origin but are similar in function are called
analogous structures.
Analogous parts
are very different in
structure, but
perform similar
functions.
Limbs of vertebrates are examples of homologous structures. See the
picture below. The wings of a bird and a fly are examples of analogous
structures.
What are vestigial structures?
• Vestigial structure—a body structure in a present-day
organism that no longer serves its original purpose, but
was probably useful to an ancestor.
What are vestigial structures?
• In some cases, a functioning structure in one
species is smaller or doesn’t function in a closely
related species.
• Vestigial structures are features that are reduced
forms of functional structures in other organisms.
• Evolutionary theory predicts that features of
ancestors that no longer have function for that
species will become smaller over time until they
are lost (disappear).
– Ex. Appendix, snake pelvis, human tails
What is convergent evolution?
• Convergent evolution occurs when
unrelated species evolve similar traits.
• Example: bird wings and fly wings