AIM: How do comparative
studies help trace evolution?
Do Now:
HW: January 2014 #49-55
How do we know we are
related to chimps &
gorillas?
COMMON ANCESTOR
Comparative Studies
• Study of similarities between
living things.
• Provides evidence of a common
origin (ancestor)
Why do scientists do comparative
studies?
To observe how closely organisms
are related to each other and see
evolutionary patterns
COMPARATIVE STUDIES
• Who are we closely related to?
• Who are we distantly related to?
Types of Comparative Studies
• Anatomy
• Embryology
• Biochemistry
• DNA and Proteins
Comparative Anatomy
• What is anatomy?
• What do you think
comparative
anatomy studies?
• Study of structural
similarities and
differences in
living things
HOMOLOGOUS STRUCTURES
• Do you see any similarities between these
organisms?
• How are they similar? How are they different?
Homologous Structures - similar structures,
different form & function. Shows
evolutionary relationships (they are related).
VESTIGIAL ORGANS
The appendix and the tail bone
are both VESTIGIAL organs.
What do they have in
common?
Vestigial structures- have no
function.
Why would an organism
possess organs with little or
no function?
They are remnants of structures
that may have had important
functions in ancestral species,
but no clear function in
modern descendants.
Hind leg in whales
ANALOGOUS STRUCTURES
• What do these two images have in common?
Insect Wing
Analogous Structures- similar form and
function, different internal structure. Does
not show evolutionary relationships.
Divergent vs. Convergent
Evolution:
Divergent Evolution- the pattern of evolution in which
species that were once similar to an ancestral species
become increasingly different.
Divergent Evolution occurs when
populations change as they adapt to
different environmental conditions.
Once related species now look different.
Convergent Evolution- the pattern of evolution
in which distantly related organisms evolve
similar traits.
Convergent Evolution occurs when unrelated species
occupy similar environments in different parts of the
world. Unrelated species now look the same.
Which is Which?
Which is the
gorilla, fish and rabbit?
Comparative Embryology
• In Comparative Embryology, related
organisms show similar embryonic
development
Comparative Biochemistry
• Comparative Biochemistry compares the
DNA or Amino Acids of an organism in order
to find relationships among living things.
The more
similar the
DNA and
Amino Acids,
the more
closely the two
organisms are
related.
Common Ancestor
• This evidence leads to the idea of:
• COMMON ANCESTRY
• All species living and extinct were derived
from common ancestors.
The Results of Genetic Variation:
1)Structural Change- the physical
features of an organism.
2)Functional Change- molecular or biochemical
changes affect how an organism works. Changes in
DNA often lead to functional changes.
3)Behavioral Change- many of the
specific behaviors today have become
common because they have resulted
in greater reproductive success.