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Natural Selection
A Mechanism for Evolutionary
Change in the genes of a population over time.
• includes fossil record, DNA and protein
studies and direct observation.
• indicates that living things on the earth
change over time.
• Example – Increasing bacterial resistance to
antibiotics. We have directly observed this
What is Evolution?
• The processes that have transformed life on
earth from it’s earliest forms to the vast
diversity that characterizes it today.
A change in the genes over time!!
(What does this mean? What will cause this?)
Fossil evidence
• Lowest levels show oldest fossilized
remains of living things
• Lower levels=simpler
• Higher levels=more complex
Charles Darwin
• Darwin read a publication
(by Charles Lyell) that talked
about how natural forces
gradually change Earth’s surface.
• He wondered if this type of gradual
change applied to living organisms…
Charles Darwin
• In 1859, he wrote:
– “On the Origin of Species by Means
of Natural Selection”
Two main points in the article:
1. Species were not created in their
present form, but evolved from ancestral
2. He proposed that NATURAL SELECTION
is the mechanism for evolution
Charles Darwin
• Proposed that Natural Selection is the
cause of evolutionary change in 1859.
• Concept of Natural Selection is AKA
“Survival of the fittest”
• In order for Natural Selection to occur,
population must include diversity (genetic
Natural Selection (4 points)
1. Genetic variation (differences) exists in
all populations.
2. Some variations are favorable
3. Not all young produced in each
generation can survive
4. Individuals with favorable variations have
a greater chance of reproducing and
passing on their variations (genes/traits).
Natural Selection is sometimes
referred to as “Survival of the
fittest”- What does this mean?
• The fittest member of a population is the
individual that produces the most
offspring…passes on the most copies of its
Which variation is favorable?
What will the next generations look like?
• w
Selective Pressures
Factors that result in selection of specific
Changes in climate or other
environmental factors
Competition for food, space, reproductive
resources…survival means passing on
Evidence of Evolution
1. Fossil Record:
Fossils and the order in which they appear in
layers of sedimentary rock (strongest
evidence). Which is older- lower or higher in
the rocks?
2. Homologous structures:
Structures that are similar because of
common ancestry (comparative anatomy)
Chapter 7
Section 1 Change over Time
Evidence of Evolution
3. Molecular biology:
Sequence comparison of DNA and
proteins (amino acids)
4. Taxonomy:
Classification of life forms- how they
compare & relate to other organisms.
• Mutations are random nucleotide changes
in the DNA (genes) of an organism.
• Some mutations are silent (no change in
the protein), some are unfavorable and
occasionally, they may be beneficial and
lead to evolutionary changes.
• Mutations result in the DIVERSITY in a
• Characteristic that helps an organism to
survive and reproduce.
• a BETTER fit between the organism and its
• The result of evolution by natural selection!
• Giraffe… neck
• Peacock… flamboyant feathers
• Bacteria… resistance to antibiotics
• Human…?
Peppered Moth- Light & Dark
Peppered Moths in England
• Majority of moths were white on light trees.
• Factories spewed out massive amounts of air
pollutants which darkened the tree trunks.
• Moths with dark coloration (camouflage)
survived to reproduce…passing on their genes
for dark color to next generation.
• Over time, population became mainly DARK
moths; This change in the genes of the
population over time = EVOLUTION!
•How do the
Peacock’s large
brightly colored
feathers help it
•Do you think these
feathers help it evade
predators or find food?
•Obviously not!
So why the
feathers? Do
they help it fly
• The feathers help
the peacock attract
a mate and thus,
pass on its genes.
• Survival fittest…not
necessarily the
Why/how did the giraffe get
such a long neck?
• Explain this using what you have learned
about natural selection ( the 4 points).
4 Main points of
Natural Selection
1. An early giraffe was born with a longer
neck…..(a CHANGE in her genes- a
2. This giraffe was able to reach the higher,
more plentiful leaves on the tree.
3. Many of her siblings with shorter necks did
not survive (not enough food!).
4. She survived and had more offspring than
other giraffes (& many of them had longer
necks like Mom!).
To summarize:
leads to
the process
of evolution!
Misconception: “Evolution is a theory about
the origin of life.”
• Response: Evolutionary
theory deals mainly with
how life changed after its
origin. Science does
investigate how life
started, but this is not the
central focus of
evolutionary theory. Most
studies of evolution are
focused on the branching
and diversifying AFTER it
Misconception: “Evolution is ‘just’ a
• Response: Scientific theories are explanations
that are based on lines of evidence, enable
valid predictions, and have been tested in many
ways. In contrast, there is also a popular
definition of theory—a “guess” or “hunch.”
These conflicting definitions often cause
unnecessary confusion about evolution.
Misconception: “Natural selection involves
organisms ‘trying’ to adapt.”
• Response: Natural selection
leads to adaptation, but the
process doesn’t involve “trying.”
Natural selection involves
genetic variation and selection
among variants present in a
population. Either an individual
has genes that are good
enough to survive and
reproduce, or it does not—but it
can’t get the right genes by
Would this mutation make you
more fit?