What is natural selection?
 It’s the process whereby organisms better adapted to
their environment tend to survive and produce more
offspring.
 The theory of its action was first fully explained by
Charles Darwin and is now believed to be the main
process that brings about evolution.
Darwin:
Process of Natural Selection:
1. Living things face a constant struggle for
survival.
2. Only strong individuals survive to reproduce.
3. Causes genetic changes gradually over many
generations.
4. Species adapt or become better suited to their
environment.
What is an adaptation?
 Is the evolutionary process whereby an organism
becomes better able to live in its habitat or habitats
What is evolution?
 A gradual process in which something changes into a
different and usually more complex or better form.
What evidence do we have of
evolution?
 The fossil record provides evidence to support the
theory of evolution.
 A scientific theory is a well-tested concept that
explains a wide range of observations.
 The fossil record shows that millions of types of
organisms have evolved. But many others have
become extinct. We can look at fossils and see changes
in the features of animals over time.
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?
Answer this question on a blank
sheet of lined paper. Then, you
must write a 4-5 sentence
summary about today’s notes IN
YOUR NOTEBOOK!!!
 Explain in 4-5 sentences why a characteristic that
helps an animal to live longer tends to become more
popularin the population over time. Be sure to
explain what evolution by natural selection has to do
with it.