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Chapter 15
Darwin’s Theory of Evolution
15-1 The puzzle of Life’s diversity
• Evolution = _________________________________________________________
• Theory = ___________________________________________________________
* A scientific theory has been accepted:
- explains a wide variety of data and observations
can be used ____________________________________
- They are not absolute, ______________________________________
and can be changed as the world view changes.
Darwin’s Theory of Evolution
• Voyage of the H.M.S. Beagle; ______________________________
• Observed finches, tortoises, and other animals on the _________________________
• Published _______________________________________________________
• Proposed “________________________________________________________”
15-2 Ideas that shaped Darwin’s Thinking
Other theories at the time …
• All life was created in just a _________________________________ and has not changed
• Hutton
- the Earth is changing & __________________________________________
• Lyell
- If Earth is changing - _______________________________________
Lamarck’s Theory of Evolution
• Inheritance of ______________________________________ (1809)
o Believed that organisms had a “_______________________________” that drove variation
o Selective ________________________________
Ex. Giraffe
• Giraffes had short necks, and “__________________” to reach high branches
• Over time they were able to _________________________________ to reach branches
• This new, _________________________________ was passed onto offspring
15-3 Darwin Presents his Case
Back to Darwin’s Theory …
What is Natural Selection??
• Based on the existence of ___________________________________
differences between ___________________________
some cows produce more milk
some plants produce larger fruit
• Farmers already used ___________________________________ to get the best livestock & crops
So now we have the idea that _____________________ does this also!
What is artificial selection?____________________________________________________________
Variation between Organisms
• ____________________________________ is the differences between organisms’ _______________
Ex. ________________________________________________________
•_______________________________________ = struggle for existence________________________
• ______________________________________
- a ________________ that makes a living thing able to
________________________ in its environment/surroundings
- This makes it an ______________________________
- Advantage is they live longer!
The advantage of living longer is ______________________________________________________
During reproduction, the organism’s _____________________ can be passed on to the offspring
The _______________________________ is thus able to be passed on to the ___________________
“Survival of the Fittest”
• Organisms with the most
pass on their traits
– The
Example: the color of the soil determines which color fur is an advantage for mice
Nature chooses!
Compare to
, when humans choose what
traits they desire and have those organisms reproduce
Mice in the Desert
When the soil is a dark color
The mice with light fur _________________________________
- The mice with dark fur are now easier to see and eaten more often by owls. It is
no longer an adaptation.
The mice with dark fur blend in well and are eaten less = __________________________________
• If the soil changes from a lot of rain and is now a light color …
The mice with dark fur are now easier to see and eaten more often by owls
Now the mice with light fur blend in and have an _____________________________
Descent with Modification
• The structural and biochemical _____________________________ among living organisms are best
explained by Darwin’s conclusion:
- Living organisms ___________________ through gradual modification of ______________
forms = descent from __________________________________________
• Without ____________________________________, there’s little chance that organisms would
have all these similarities
What ways are we similar?________________________________________________________________
MCAS Essay
The graph below relates the number of gray squirrels in a
small population to their coat colors.
o This squirrel population has been separated from other
squirrel populations by a new highway and several
construction sites. The main predators of these squirrels
are cats and hawks.
a. Assume that dark gray squirrels are very visible in
this new environment. What is likely to happen to
the distribution of coat color in this squirrel
population over several generations? Sketch a graph
in your Student Answer Booklet to show the
predicted distribution, and explain your answer.
b. Assume that dark gray squirrels are very visible
on the ground, and light gray squirrels are very
visible in the trees. Explain what is likely to happen
to the distribution of coat color in the squirrel
population over several generations. You may
sketch a graph in your Student Answer Booklet as
part of your explanation.
Conditions needed for Evolution
1. __________________________________________________________________
2. __________________________________________________________________
3. __________________________________________________________________
a. Is competition within a niche
b. Niche: a specific role (job) of an organism within a community
4. __________________________________________________________________
Where is the EVIDENCE??
Evidence for Evolution
• __________________________________________-evolution takes a long time
- Originally thought it was 240 million years old
- Now it is known to be 4.5 billion years old
• __________________________________________
- Fossil - ____________________________ of something once living
- Found trapped in ice, sap, or sedimentary rock
• ___________________________________________
- Organisms that have a __________________________________ develop in the same
manner & thus often look alike
• ____________________________________________
- Similar DNA sequences
Age of the Earth-rocks help us see how organisms change over time
° Layers of rocks represent time
_______________rocks on bottom, newer on top
° ____________________________ - a fossil found at bottom is older than one found
at the top
° ____________________________ - certain radioactive elements decay at a
Predictable rate (_________________)
• ___________ of the radioactive element decays into a different element in
X number of years
• Carbon-14 decays to nitrogen in 5770 years
• If you started with 1 gram – after 5770 yrs. You’ll have ____________
• After 11,549 yrs. You’ll have _______________
Geologic Time Scale
Fossil Record
° Collection of fossils put together to represent the history of
° Problem with this record: ____________
some living things were not preserved because they did not have “bony” parts
some living things did not live in area where fossils were made
° Need _______________ to make fossils (near flowing water)
Comparative Anatomy
° Early Development
• ___________________ - organism at early stage of development (before birth)
° All _______________________ begin to develop the same way
- Any major ____________ changes here would have caused so much change the organism
would not survive
° Homologous Structures
• Structures that develop from
______________________, but have different uses
° Analogous Structures
• An appendage has the ______________________
but a __________________ internal structure
Example: Wings are for flying, but a bird wing
has bones & a butterfly wing doesn’t
° Vestigial Structures
• A trace of a structure that is no longer useful
Examples: Human tailbone and Whale hips
Molecular Biology
• All organisms have ___________ made of the same nucleotides
Also share________________________________
• The more similar two organisms’ DNA is, the more likely they share a _____________
- Chimps & gorillas are 97.9% the same
- Humans & chimps are 98.4% the same
• Maternal Mitochondrial DNA
MCAS Essay
The illustrations below show a
South American finch and
some of the species of finches
found on the Galápagos
Islands. The map shows the
relationship of the Galápagos
Islands to the west coast of
South America.
o There are 13 species of
finches found on the
Galápagos Islands. These
finches have a wide
variety of food sources and
beak shapes. There is one
genetically similar species
of finch found on the
South American mainland.
This finch eats small
Use the map and the bird
illustrations to identify and
explain two ways that these finches provide evidence that supports the theory of evolution.
Chapter 16
Evolution of Populations
16-1 Genes and Variation
Darwin did not know about ___________________________
How did traits get inherited?
How did variation appear?
1930’s – scientists connected Darwin & Mendel’s works
Variation & Gene Pools
● Population = ____________________________________________________________
● When you combine all the genes they share it is called the _____________________
- Ex. Rattlesnakes genes indicate no legs, scales covering their bodies, long tongues, different
Color patterns
● How common the gene is, is it’s ________________________________________
allele for
brown fur
allele for
black fur
Frequency of the allele for
brown fur is
Frequency of the allele for black
fur is =
Evolution is …
● Any change in the ______________________________ of alleles in a _________________
Ex. Mice (above)
● 40% frequency of ______
● 60% frequency of ______
● If this changes to 30% B – the population is _____________________________!!
Where does all of this VARIATION come from?(tie in meiosis and mutation)
1. _____________________________
● _____________________________ are helpful ______________
● ____________________ come from ______________________
New traits come from new genes
● New ___________________ come from _____________________________
Mutation = ____________________________________
● Mutations can be
2. _______________________________________
From __________ pairs you can get _____________ million combinations of genes!!
16-3 The Process of Speciation (simply means making of new species)
How have new species formed?
The Result of Evolution is …
● New species are formed
● ______________________________
A group of _____________________________________able to produce
_____________________ offspring
● ___________________ = able to make eggs or sperm
● ___________________ = NOT able to reproduce
● A new species is defined when two ___________________________ are no longer able
to produce _____________________ offspring
Often result of ____________________ adding up
Ex. A labradoodle is __________________________
● the poodle & Labrador are the _______________________ species
A Mule is ________________________
● the horse and donkey are ________________ the same species
How do new species form?
● Result of ____________ species becoming SO different from the original it is now a 2nd species
Ex. Adaptation lab – all started with a hand, now you have 5 different species
- the tweezers, the fork, the small spoon, the large spoon & the chopsticks
Ex. Finches on Galapagos Islands
How speciation happens …
__________________________________________________ (mainland vs. island)
– Now no longer able to “mingle” with original population due to geographic features (canyons,
oceans, rivers, etc.)
______________________________________________ while populations are separate. Caused by:
– Mutations (good adaptations stay )
– Gene shuffling from sexual reproduction
__________________________________________– when members of a species can no longer
reproduce for various reasons (if they get back together)
– Called _______________________________
____________________________________________________ creates BIOdiversity
– Ex. mainland finches are different from island finches.
Types of reproductive Isolation
1. _____________________________ (courtship) such as different mating calls or dances
2. _____________________________ (place) such as a river, island or mountain getting in the
3. ___________________________ (time) in terms of when the population is ready to mate
17-4 Patterns of Evolution
1. Mass Extinction
● A ____________________________________
- Usually due to the _______________________ suddenly changing
- 99% of all life now extinct
- 5 major mass extinction events
- Ex. Dinosaurs
2. ___________________________________ (aka divergent evolution)
● This is most common form, such as Darwin’s finches
● An original group of species evolves into ___________________ different species best
suited to different environments
3. ______________________________________
● Unrelated species (____________________________) that look alike
Ex. Swimming species like fish, sharks, penguins & whales
4. __________________________________
● Changes occur slowly and gradually
5. ______________________________________
● Long periods of NO change with brief periods of sudden change
Ex. Peppered moths
Or no Evolution at all …
● _______________________________________________________
● Some species are well adapted to live in their environment and haven’t changed for hundreds of millions of
● They are called ________________________________
Ex. Horseshoe crab, coelacanth, frilled shark