A Closer Look At Darwin’s Idea of

Natural Selection

Jarod RaithelMary Carroll High SchoolHonors Biology ISpring 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 BearOur story begins with the Polar

Bear’s closest living relative – the Brown Bear

The Evolution of The Polar BearAround 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 BearBecause of the genetic mutation,

a litter of Brown Bears exhibited WHITE coloration

The Evolution of The Polar BearHow 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

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

REMEMBER: Natural Selection Rests on 4 Premises:

X

X

X

X

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.

REMEMBER: Natural Selection Rests on 4 Premises:

X

X

X

X

X X

X

XX

XX

X

X

X

X

X

X

X

X

XX

X

X

X

X

X

X

XX

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!