A Closer Look At Darwin’s Idea
of Natural Selection
Jarod Raithel
Mary Carroll High School
Honors Biology I
Spring 2007
Natural Selection Rests on 4 Premises:
1) There is variation in the traits of
individuals within a population
Natural Selection Rests on 4 Premises:
1) There is variation in the traits of
individuals within a population
Natural Selection Rests on 4 Premises:
1) There is variation in the traits of
individuals within a population
Natural Selection Rests on 4 Premises:
2) There is differential survival and
reproduction, i.e., some individuals
survive and reproduce, some don’t
Natural Selection Rests on 4 Premises:
2) There is differential survival and
reproduction, i.e., some individuals
survive and reproduce, some don’t
Natural Selection Rests on 4 Premises:
2) There is differential survival and
reproduction, i.e., some individuals
survive and reproduce, some don’t
Natural Selection Rests on 4 Premises:
2) There is differential survival and
reproduction, i.e., some individuals
survive and reproduce, some don’t
Natural Selection Rests on 4 Premises:
3) Traits have a genetic basis, or are
inherited from parents
Natural Selection Rests on 4 Premises:
3) Traits have a genetic basis, or are
inherited from parents
Natural Selection Rests on 4 Premises:
4) Advantageous traits, which allows
organisms to have more offspring, will
become more common in the population
over time.
Examples of Natural Selection:
The Evolution of The Polar Bear
Our story begins with the Polar Bear’s
closest living relative – the Brown Bear
The Evolution of The Polar Bear
Around 300,000 years ago a small group of
Brown Bears became reproductively
isolated from the rest of the population
The Evolution of The Polar Bear
This small founding
population of Brown
Bears were able to
survive and
reproduce living in
the Arctic Tundra.
After MANY
generations, a
random genetic
mutation occurred
...
The Evolution of The Polar Bear
Because of the genetic mutation, a litter of
Brown Bears exhibited WHITE coloration
The Evolution of The Polar Bear
How do you think the white fur color affected
these bears chances of surviving long
enough to have cubs of their own?
REMEMBER: Natural Selection Rests on 4 Premises:
1) There is variation in the traits of
individuals within a population
REMEMBER: Natural Selection Rests on 4 Premises:
2) There is differential survival and
reproduction, i.e., some individuals
survive and reproduce, some don’t
REMEMBER: Natural Selection Rests on 4 Premises:
2) There is differential survival and
reproduction, i.e., some individuals
survive and reproduce, some don’t
X
X
X
X
REMEMBER: Natural Selection Rests on 4 Premises:
3) Traits have a genetic basis, or are
inherited from parents
REMEMBER: Natural Selection Rests on 4 Premises:
4) Advantageous traits, which allows
organisms to have more offspring, will
become more common in the population
over time.
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X X
X X
X
X
X
X
X
X
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X
X
X
X
What Happened?
Through Reproductive Isolation and
Natural Selection . . .
One Species Evolved Into Another
New Species By Adapting To Its
New Environment
We see this trend again and again in the
Animal Kingdom . . .
Speciation by means of
Reproductive Isolation & Natural Selection!