Transcript File

Have you seen this famous image?
What do you think this image represents?
This image suggests that humans evolved
directly from chimpanzees (step by step).
Is it true? Did humans evolve directly from chimps?
NO - humans did NOT evolve directly from chimps. This is
a very common misconception!
The Relationship Between Humans & Chimps
• The human species did not evolve
directly from chimps.
• HOWEVER, humans & chimpanzees are
VERY closely related!
• Humans & chimpanzees share a recent
common ancestor.
• This means that millions of years ago, an
ape-like species gave rise to 2 distinct
lineages – the human-like species & the
great apes living today.
Who was the last common ancestor to humans &
chimps?
• This is one of biology’s unanswered questions – we don’t
know for sure who our last common ancestor was.
Sahelanthropus tchadensis
may represent our CA.
Proof of Similar
Ancestry
How do we know an
organism is closely related
to another?
How can we find proof of similar ancestry?
•
•
•
•
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Embryology
Homologous Body Structures
Analogous Body Structures
Vestigial Body Structures
Genetic Similarities (DNA)
Embryology
• The early stages of vertebrate development are all very
similar.
Vertebrates start to
diverge into chimp,
chicken, & lizard form
in the later stages of
development.
What does this say about the relationship between
vertebrates?
Does this provide
evidence that
vertebrates share a
common ancestor?
YES!
Vertebrate embryos develop the same characteristics as they
develop.
These genes were probably inherited from a common ancestor.
Larvae are the immature stage of an organism that looks
different from the adult form. For example, a caterpillar
is the larva of a butterfly.
The larvae of modern sea stars, which are invertebrates,
resemble some simple vertebrate larvae. This similarity
may suggest that simple vertebrates…
A.
B.
C.
D.
Share a common ancestor with sea stars.
Evolved from sea stars.
Evolved before sea stars.
Belong to the same species of sea stars.
Simple vertebrates share a common ancestor
with sea stars!
Compare the bone structure of these
mammals’ forearms.
Homologous Body Structures
• Structures derived from a common ancestor or the
same evolutionary or developmental origin
Homologous Body Structures
Developmentally, a human arm, whale fin, cat leg, & bat
wing share the same bones.
Due to living in different environments & different selective
pressures, these bones can have dramatically different functions!
What can you say about
the relationship between
species who share
homologous structures?
Species who share
homologous structures share
a common ancestor – they
are related!
Analogous Structures
• Structures that seem similar,
but they DO NOT share a
recent common ancestor
Compare the wing of the bird to
the wing of the moth.
What do they have in common?
What are some differences?
Analogous Structures
• The wing of the bird & the wing of the insect are similar
in function (flight), but are different in structure (bones
vs. no bones) & different in embryonic origin.
These wings evolved separately to
perform a similar function (due to
similar selective pressures acting
on the species).
What can you say about the relationship between
species who share analogous structures?
Species who share analogous structures DO NOT share a
recent common ancestor – they are NOT closely related!
The bones of the dinosaur & bird
A.
B.
C.
D.
Homologous
Analogous
Both
Neither
From left to right: insect, dinosaur, bird, bat.
Homologous Structures!
The wings of the bat & insect
A.
B.
C.
D.
Homologous
Analogous
Both
Neither
From left to right: insect, dinosaur, bird, bat.
Analogous Structures!
Vestigial Structures
• Structures that have become reduced in size, because
they do not have a true contributing function or role in
survival
Whales have the remains of pelvis &
leg bones from their walking ancestors!
Vestigial Structures
• If you take an x-ray of a snake, you will find pelvic &
femur (thigh) bones.
What do these vestigial
structures mean?
Snakes evolved from an
ancestor that had legs!
Basically…
• Homologous Structures: similar structures, used for
different functions
– Shows that the species share a recent common ancestor &
are closely related
• Analogous Structures: different structures, used for
similar functions
– Shows that the species do NOT share a recent common
ancestor & are NOT closely related
• Vestigial Structures: no longer have function or use
– Shows that the species evolved from another species that
used the structure
Dolphins (mammals) & fish both have similar
body shapes adapted for moving in water.
A. Homologous
B. Analogous
C. Vestigial
Analogous Structures!
Similar functions (swimming),
but mammals & fish are not
closely related!
This species of cave-dwelling salamander has
eyebuds, but is completely blind.
A. Homologous
B. Analogous
C. Vestigial
Vestigial!
The fact that this blind salamander still has
eyebuds shows that, though blind, has evolved
from an ancestor who had eyes & was not blind!
Humans, whales, & giraffes all have 7 neck bones.
A. Homologous
B. Analogous
C. Vestigial
Homologous!
Similar neck
structures, different
functions!
The ear muscles, appendix, & tailbone in humans.
A. Homologous
B. Analogous
C. Vestigial
Vestigial!
Indicates that 2 organisms probably have a
common ancestor.
A. Homologous
B. Analogous
C. Vestigial
Homologous Structures!
Genetic Data
• We can compare DNA sequences between species
to see how similar or different they are.
Here is a short section of DNA. What do the A, T, G,
and C represent?
A
C
A
T
A
T
T
A
G
Now compare the DNA to a close ancestor:
Living organism:
A
C
A
T
A
T
T
A
G
A
T
A
T
T
A
C
Ancestor:
A
T
On which nucleotide(s) do the sequences differ?
What is this difference called?
You try it!
1. You have 9 nitrogen base sequences from a section
of DNA similar to what you might find in a human.
Look for the sequence labeled “living DNA”.
2. Find the closest ancestor to the living DNA and
place it below the living DNA
3. Place the rest of the sequences in the correct order,
from present (living) to oldest ancestor.
What did you use to make your decision?
Were you correct in your order?
Assume the rate of
mutation is 1
mutation for every
10,000 years.
How many years
separate the “living
DNA” from its oldest
ancestor?
The table below shows chemicals found in certain
bacteria. Each capital letter represents a different
chemical. Which 2 bacteria are most closely related?
A.
B.
C.
D.
Bacteria 1 & 2
Bacteria 2 & 3
Bacteria 2 & 4
Bacteria 3 & 4
Bacteria
Bacteria 2 & 4!
Chemicals Present
Bacteria 1
A, G, T, C, L, E, S, H
Bacteria 2
A, G, T, C, L, D
Bacteria 3
A, G, T, C, L, D, P, U, S, R, I, V
Bacteria 4
A, G, T, C, L, D, H
Descent with Modification
• Species alive today are descended with modifications
from ancestral species that lived in the distant past.
This process by which diverse
species evolved from a
common ancestor unites ALL
organisms on Earth into a
single tree of life!