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Theory of Natural
Selection
Power Notes
Mrs. Riordan
What is your definition of Evolution?
The
slow change in
organisms that occurs over
many generations.
Natural Selection is:
 The
process by which organisms
change over time, as those best suited
to their environment survive to pass on
their genes to the next generation.
Population:
All
Members of a species living in
a given area at a given time.
Key insights that led Darwin to the
theory of evolution:

Artificial selection- Darwin noticed a lot of variation of
traits in domesticated animals and plants. Humans can
increase the chances of certain traits being passed down.

Heritability – Natural Selection can only act on traits that
already exist. Traits must be heritable in order to be
passed down

Struggle for survival – There is only so much food and
resources available so only the most “fit” survive.
4 main principles of natural selection
 Principle
Sexual
1: Variation:
reproduction and
mutations contribute to
variation within a gene
pool.
Principle 2: Overproduction
 Individuals
tend to produce more
offspring than the environment can
support. (over-population /
competition).
Principle 3 : Adaptation
 An
adaptation is a change in an
individual in order to fill a niche or
survive in its environment. Adaptations
add up over time to drive Natural
Selection.
Principle 4: Inheritance of traits

Individuals that are better able to cope
with the challenges presented by their
environment tend to leave more offspring
than those individuals less suited to the
environment (Inheritable characteristics).
Fitness
Is
a measure of survivability and
the ability to produce offspring
Survival of the Fittest
Another
word for natural
selection. Organisms that are best
adapted to the environment
survive to pass on their genes to
the next generation.