This document contains notes from a science class on evolution and common ancestry. It includes definitions of key terms like inheritable vs. acquired traits, common ancestors, and evidence that indicates common ancestry. Examples used to illustrate the concepts include the Galapagos finches and how their beak variations evolved due to different food sources on different islands, as well as molecular evidence from similar DNA sequences. Students are prompted to answer questions drawing on these concepts.

1. Assign Yourself: IA2 Review (both
sides)
• Take out your science journals—we are going
to grade them.

2. Announcement:
• 1st dissection taking place THIS FRIDAY

3. Take out your science journal! We are
going to grade it!

4. Common Ancestors

5. What kinds of traits can be inherited?
• Only inheritable traits (genetic traits) can be passed
from parents to offspring.
Examples: eye color, height
• Acquired traits (anything not controlled by genes),
CANNOT be passed on.
Examples: tattoos, dyed hair, injuries

6. What happens when 2 populations of the same
species are living in different environments?
• Over time, natural selection causes populations to
change so they are better adapted to (better at
surviving in) their environments.
• If 2 populations are living in different environments,
they might change so that each one is better
adapted to its own environment.
Example: Birds living on the Galapagos islands

7. Processing Piece:
• Look at the birds in this picture. What variation
(different traits) do you see?
• Why might they have this variation?

8. Processing Piece:
• In a population of birds, some birds had thin beaks
and some birds had large, thick beaks. Thin beaks
were better for grabbing insects, and thick beaks
were better for cracking seeds. The birds migrated
to two island habitats. One island had lots of
insects, and the other had lots of seeds. What do
you predict would happen to the populations on
the different islands?

9. What are the Galapagos finches?
• Different species of finches,
each living on one of the
Galapagos islands
• Each has its own type of
beak
• Each beak is good for eating
the food source most
common on that island.
• The finches all share a
common ancestor.

10. What is a common ancestor?
An individual or species that was alive in the past,
that 2 or more different groups of organisms alive
today are descended from.

11. Processing Piece:
• Look at the birds in the picture below. Circle the one
that you think is the common ancestor.

12. What is a phylogenetic tree?
Like a family tree that shows the relationships
between different species or populations.

13. Processing Piece:
• Circle the most recent common ancestor of…

14. Processing Piece:
• Based on this tree, which is most closely related to
birds: crocodiles or turtles?

15. Processing Piece:
• Based on this tree, which is most closely related to
lizards: crocodiles or mammals?

16. What are 2 ways we can tell that 2 groups
probably share a recent common ancestor?
1) Biogeography clues – when species that are very
similar live near each other, but are separated, it’s
likely that they came from a common ancestor.
Example: birds on the Galapagos islands

17. What are 2 ways we can tell that 2 groups
probably share a common ancestor?
2) Similar nucleotide sequences – when the DNA of
two different species is similar, it’s likely that they
share a common ancestor.
Nucleotide = bases (A, T, G, and C)
Sequence = the order that they’re in

18. Processing Piece:
• Write “Evidence for Common Ancestry.”
• Underneath it write “2. Nucleotide Sequences” and
draw a picture to help yourself remember the
definition.
Example:
AAT TAG AAT GCA
AAT TAC AAT CCA
CCA GGT CAG TTA
Share a common
ancestor

19. Exit Ticket
1. What is the difference between an
inheritable trait and an acquired trait?
2. What is a common ancestor?
3. Name 2 types of evidence that indicate
organisms might share a common ancestor?