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Transcript
Theory of Natural Selection
Darwin Proposed the Theory of
Natural Selection to Explain
Evolution

Evolution, or change over time, is the process
by which modern organisms have descended
from ancient organisms.

A scientific theory is a well-supported
testable explanation of phenomena that have
occurred in the natural world.
Ideas that Shaped Darwin’s Thinking
James Hutton:



Proposed a theory of
geological change
States that natural
forces change earth’s
surface shape
States that these
changes are slow and
the Earth was much
older than thousands
of years
Ideas that Shaped Darwin’s Thinking
Charles Lyell



Wrote the book
“Principles of
Geography”
States that
geographical features
can be built up or torn
down
Darwin thought if
earth changed over
time, what about life?
Ideas that Shaped Darwin’s Thinking
Jean Baptist Lamark



Proposed that species
change with a tendency
toward perfection
(Giraffe necks)
Traits that are used are
passed down to offspring
Traits that are not used
are not passed down
Ideas that Shaped Darwin’s Thinking
Thomas Malthus
 19th century English
economist who wrote
“On the Principle of
Population”
 Stated that if a
population grew too
large, then there would
be insufficient living
space and a lack of
food so population
would decline
• Populations
tend to rise and
fall overtime
• As the
population
decreases, food
supply returns
• As food supply
returns,
population
grows again
Ideas that Shaped Darwin’s Thinking
Selective Breeding The process of humans selecting traits
they want to appear in offspring to
produce desired traits
 Used in farming to create sheep with fine
wool
 Used to create different breeds of dogs
and cats
Ideas that Shaped Darwin’s Thinking
Russell Wallace

wrote an essay
summarizing
evolutionary change
from his field work in
Malaysia

Gave Darwin the drive
to publish his findings
Darwin’s Conclusion:
Evolution happens through the
process of natural selection!



Also called “Survival of the Fittest”
Some individuals are better suited for their
environment
These individuals will survive and reproduce
better than the others
These favorable traits will be passed down in
offspring and appear more in future generations
Natural Selection


Over time, natural
selection results in
changes in inherited
characteristics of a
population.
These changes
increase a species
fitness in its
environment
Requirements for Natural Selection
Overproduction:
There must an
overproduction of
offspring so that
some can live
while others will
die.
Requirements for Natural Selection
Genetic Variation:
There must be
differences among the
individuals so that
some do better than
others.
Ex. Color, aggression, intelligence, behaviors, speed
Requirements for Natural Selection
Competition:
There must be a
struggle to survive
due to limited
resources.
Ex. Limited resources could include food, water, shelter,
mates, territory
Requirements for Natural Selection
If none are able to, then the
population will go extinct!
Successful
Reproduction:
There must be
successful
individuals who
pass down their
favorable traits to
offspring.