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I. Natural Selection
Who Lives
Who Dies
A. Darwin Proposed 2 Things
1.
2.
Evolution occurs
Evolution occurs due to Natural Selection

Who do you think chooses who sticks
around and who doesn’t?
The Environment
B.
The environment chooses which
organisms will survive and reproduce
based on their phenotype
C.
Steps to Natural Selection
1.
Variation is the raw material for natural
selection
a. Within a population there is a
variation in traits (phenotypes)
2.
Living things face a constant struggle for
existence
a. Produce more offspring than there is
room and food for, so they must compete
to survive
3.
Only some individuals survive and
reproduce
a. Some individuals are more “fit” for the
environment or for life in general
ex. Resistance to disease
4. Natural selection causes genetic change
a. Each generation consists of individuals
with traits(phenotypes) that made them
more “fit”, so over time, alleles for those
traits will increase in frequency
5.
Species adapt to their environment
a. selection tends to make organisms
better suited to their environment
C. Lethal genes are kept in the gene pool if
in the heterozygous form because those
individuals will not show the lethal
phenotype