1. Comparative Anatomy
Scientists can compare the anatomy of different organisms to figure out how closely they are related.
Anatomy = body structure
Remember, the theory of evolution tells us that all life branched off from one original species (red circle) and the more closely two organisms are related, the more recently they shared a common ancestor

2. Homologous Structures
Similar in Origin
Different in Function (bird wing/human arm)
Recent common ancestor
May appear in embryonic development and disappear before birth.
Key Point #1: Homologous features are those that have similar structure but different functions.

3. Homologous Structures=recent common ancestor!!

4. Analogous Structures
Analogous structure: Parts of different species that have the same function, but EVOLVED SEPARATELY
Key Point #2: 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.
Unrelated* (with a star) because no organisms are ACTUALLY unrelated, given that we all descended from the same original organism. But it’s easier to say unrelated than it is to say “organisms with no recent common ancestor” over and over.
Introduce definition first (explicitly state that this is satisfying our first objective), KP explains why it’s important (b/c it provides a certain sort of evidence for evolution… hey, our second objective!). Then, CFU: can you explain to me how analogous structures support evolution? (All they have to do is spit KP back out at you… but make sure they can do it.)

5. No recent common ancestor!!!
Insect, bird, and bat wings evolved completely separately. Unrelated organisms will evolve similar adaptations in response to similar environmental pressures!
No recent common ancestor!!!

6. 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!

7. Vestigial Structures
Vestigial structure: Part of an organism that is no longer used for anything
Key Point #3: 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

8. Letter “c” = hind legs of a baleen whale skeleton
Vestigial = no longer used!!!

9. Blind salamanders have eye sockets!?!?
They live in caves. Siiick.

10. So, what about me?

11. 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
* because, technically, everything is (at least distantly) related. But the point is that they don’t share a recent common ancestor.
If you can’t find the answer…
ADD IT!!!

12. 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
That organisms have adapted due to different habitats and necessities, so they no longer need those structures.
If you can’t find the answer…
ADD IT!!!

13. HOMOLOGOUS Guided Practice (GP)
Are these structures…
(A) Homologous, (B) Vestigial, (C) Analogous?
Human embryos and cat embryos both have gill slits.
After revealing the correct answer, ask random students to explain how the structure supports evolution
HOMOLOGOUS

14. ANALOGOUS 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.
After revealing the correct answer, ask random students to explain how the structure supports evolution
ANALOGOUS

15. VESTIGIAL 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.
After revealing the correct answer, ask random students to explain how the structure supports evolution
VESTIGIAL

16. 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.
After revealing the correct answer, ask random students to explain how the structure supports evolution
VESTIGIAL

17. HOMOLOGOUS Guided Practice (GP)
Are these structures…
(A) Homologous, (B) Vestigial, (C) Analogous?
Cat embryos and human embryos both have tails.
After revealing the correct answer, ask random students to explain how the structure supports evolution
HOMOLOGOUS

18. ANALOGOUS Guided Practice (GP)
Are these structures…
(A) Homologous, (B) Vestigial, (C) Analogous?
Dolphins and sharks both have fins, but they evolved completely differently.
After revealing the correct answer, ask random students to explain how the structure supports evolution
ANALOGOUS

19. HOMOLOGOUS 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).
After revealing the correct answer, ask random students to explain how the structure supports evolution
HOMOLOGOUS

20. VESTIGIAL 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.
After revealing the correct answer, ask random students to explain how the structure supports evolution
VESTIGIAL

21. ANALOGOUS 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.
After revealing the correct answer, ask random students to explain how the structure supports evolution
ANALOGOUS

22. Embryo An early stage in the development of an organism
Often embryo’s have structures that are not present after the organism is born
Human Embryo
Cat Embryo
All the above have folds called gill pouches in the neck region. All similar by the fact they are all vertebrates.

23. Embryology The study of embryos.
The chemical make-up of organisms also provides clues to common ancestry.
Example: Scientist compare the sequences of the nucleotides in DNA and the amino acids making up certain proteins in different organisms. The more similarities found in 2 DNA or amino acid sequences, the more closely related the organisms are.
Example: Hemoglobin blood in chimpanzee’s is more similar to human hemoglobin than a cats hemoglobin is to a human. ( Chimpanzees and humans are more closely related)

24. Exit Question: Choose one option Write in complete sentences!
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.
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.
Student Choice – there’s a WOW factor!