A Closer Look At Darwin’s Idea of Natural Selection

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 also know as fitness

Natural Selection Rests on 4 Premises:
2) There is differential survival and reproduction, i.e., some individuals survive and reproduce, some don’t

2)
Fitness
There is differential survival and reproduction , i.e., some individuals survive and reproduce, some don’t

2)
Fitness
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

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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

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!