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LEARNING TARGETS
Describe the factors that Darwin considered when developing his
Theory of Evolution.
Explain the process of natural selection and how it leads to descent
with modification.
Describe the significance of genetic variation within a population and
identify sources of genetic variation.
Describe how evolution occurs through changes in gene pools, including
genetic drift, gene flow, and sexual selection.
DARWIN AND NATURAL
SELECTION
EVOLUTION IS A THEORY – JUST LIKE EINSTEIN'S THEORY OF
GENERAL RELATIVITY, WHICH HELPS TO EXPLAIN GRAVITY!
•Evolution is a well
supported explanation of
phenomena that have
occurred in the natural
world
•A theory in science is a
well tested hypothesis, not
just a guess

CHARLES DARWIN (1809-1882)
SAILED AROUND THE WORLD 1831-1836

WHAT DID DARWIN’S
TRAVELS REVEAL
The diversity of living
species was far greater than
anyone had previously
known!!
These observations led him
to develop the theory of
evolution!!

DIVERSITY ON THE GALAPAGOS
Each island had its
own type of tortoises
and birds that were
clearly different from
other islands.
GALAPAGOS TORTOISE

INFLUENCES ON DARWIN’S THEORIES




Theories of geologic change set the stage
for Darwin’s theory
Fossils: traces of organisms that
existed in the past.
Theory of catastrophism states that
natural disasters like floods and
volcanic eruptions have shaped
landforms and caused species to go
extinct.
Theory of gradualism states that
changes in landforms resulted from
slow changes over a long period of
time.
Theory of uniformitarianism states
that the geologic processes that shape
Earth are uniform through time
(Charles Lyell’s theory).
INFLUENCES ON DARWIN’S THEORIES
Lyell argued that the earth is many millions
of years


layers of rock take time to form
processes such as volcanoes and earthquakes shaped the earth and still
occur today

INFLUENCES ON DARWIN’S THEORIES
Jean-Baptiste Lamarck:

Theory of acquired
characteristics
Organisms acquired traits by
using their bodies in new ways
These new characteristics were
passed to offspring
Lamark was wrong!

INFLUENCES ON DARWIN’S THEORIES
Thomas Malthus
 If the human population
continued to grow unchecked,
sooner or later there would be
insufficient living space and
food for everyone
INFLUENCES ON DARWIN’S THEORIES
Artifical Selection: Process in which humans change a species by
breeding it for certain traits. Examples: Dog breeds, livestock, crops,
vegetables, ect.

DARWIN’S THE ORIGIN OF SPECIES (1859)
 Other naturalists, like Alfred Wallace, were
developing the same theory as Darwin’s
Even though Darwin was afraid of the Church’s
reaction to his book he wanted to get credit for his
work.

SUMMARY OF DARWIN’S THEORY OF
EVOLUTION BY NATURAL SELECTION
1. Organisms differ; variation is inherited
2. Organisms produce more offspring than survive
3. Organisms compete for resources
4. Organisms with advantages survive to pass those
advantages to their children (“survival of the
fittest”)
5. Species alive today are descended with
modifications from common ancestors
SUMMARY OF DARWIN’S THEORY POINT 1 OF
5
Organisms differ; variation is
inherited
OBSERVED
THEORY
OBSERVED
?
HYPOTHESIS
Discuss …
SUMMARY OF DARWIN’S THEORY POINT 2 OF
5
Organisms produce more offspring
than survive
OBSERVED
THEORY
OBSERVED
?
HYPOTHESIS
Discuss …
SUMMARY OF DARWIN’S THEORY POINT 3 OF
5
Organisms compete for resources
OBSERVED
THEORY
OBSERVED
?
HYPOTHESIS
Discuss …
SUMMARY OF DARWIN’S THEORY POINT 4 OF
5
Organisms with advantages survive to pass
those advantages to their children
OBSERVED
THEORY
OBSERVED
?
HYPOTHESIS
Discuss …
SUMMARY OF DARWIN’S THEORY POINT 5 OF
5
Species alive today are descended with
modifications from common ancestors.
THEORY, much
OBSERVED
THEORY
evidence exists
?
HYPOTHESIS
END OF DAY 1 NOTES
Write a two sentence summary of the first half of
your notes in the summary section.
BELLRINGER
Who is Charles Darwin? What influenced Darwin’s Theory of
Evolution? What does descent with modification mean?

WHAT IS EVOLUTION?
 changes in living
organisms over time
 explains how modern
organisms have
descended from ancient
organisms

FITNESS AND ADAPTATION
Organisms compete for limited resources and some organisms are
more “fit” than others
Fitness – the ability of an individual to survive and reproduce in its
specific environment
Adaptation – any inherited characteristic that increases an
organism’s chance of survival, including reproduction

WHAT DETERMINES SURVIVAL?
 Traits that help individuals survive
 survive predators
 survive disease
 compete for food
 compete for territory
 Traits that help individuals reproduce
 attracting a mate
 compete for nesting sites
 successfully raise young

NATURAL SELECTION
1.
There is variation (difference in the physical traits of an
individual from those of other individuals in the group)
in traits.
For example, some beetles are green and some are
brown.
2.
There is differential reproduction.
Since the environment can’t support unlimited population
growth, not all individuals get to reproduce to their full
potential. In this example, green beetles tend to get eaten
by birds and survive to reproduce less often than brown
beetles do.

NATURAL SELECTION
3.
There is heritability.
The surviving brown beetles have brown baby beetles
because this trait has a genetic basis (trait is passed down
from one generation to the next).
4.
End result: Natural Selection
The more advantageous trait, brown coloration, which
allows the beetle to have more offspring, becomes more
common in the population. If this process continues,
eventually, all individuals in the population will be brown.

NATURAL SELECTION
Over time, natural selection results in changes in the inherited characteristics of
a population.
These changes increase a species’ fitness in its environment.
Species: Group of organisms so similar to one another that they can reproduce
and have fertile offspring.
SOURCES OF GENETIC VARIATION
Genetic Variation is stored in a populations Gene Pool, which is the
combined alleles of all of the individuals in a population.
Each allele exists at a certain rate in a population. Allele Frequency, is
a measure of how common a certain allele is in the population.

SOURCES OF GENETIC VARIATION
Gene flow – movement of genes from one population to another (migration)
Mutation – any change in a sequence of DNAMain Source
 Some mutations can affect an organism’s fitness while others have no
effect on fitness.
Recombination –(occurs during meiosis) Main Source
 Independent assortment
 Crossing over
 Sexual reproduction
EVOLUTION AS GENETIC CHANGE
Natural selection determines which alleles are passed from one
generation to the next.
As a result, it can change the relative frequencies of alleles in a
population over time.
Evolution is any change in the relative frequencies of alleles in a
population’s gene pool.
Evolution acts on populations, not on individuals.
*Remember: Populations
include individuals of the
same species living in an
area.
GENETIC DRIFT
Natural selection is not the only source of evolutionary change
Genetic drift – random change in allele frequency
In small populations, individuals that carry a particular allele may leave
more descendants than other individuals, just by chance.
Over time, a series of chance occurrences of this type can cause an allele
to become common in a population.
BOTTLENECK EFFECT
Mechanism of genetic drift, occurs after an event drastically reduces
the size of a population. This causes the population to have very little
variation. The reason for this is that certain alleles have become fixed
in the population and others have been lost.
FOUNDER EFFECT
Occurs when a small group of individuals colonizes a new habitat.
Members of the colony may carry alleles in different relative frequencies
than the larger population from which they came.
If so, the population that they found will be genetically different from the
parent population.
SEXUAL SELECTION
Certain traits increase mating success, so these traits will be passed
down from generation to generation.