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The Theory of Evolution
In science, theories are
statements or models
that have been tested and
confirmed many times
Some important properties of
theories :
They explain a wide variety of data and
 They can be used to make predictions
 They are not absolute, they serve as a
model of understanding the world and can
be changed as the world view changes
 In science, the term “Theory” does not
express doubt
The Theory of
Evolution is
considered a
Unifying Theory
of Biology
because it
answers many
questions and
explains many
Lamarck's Theory of Acquired
According to Lamarck,
organisms altered their
behavior in response to
environmental change.
Their changed behavior,
in turn, modified their
organs, and their
offspring inherited those
"improved" structures.
Giraffes developed
their elongated necks
and front legs by
generations of
browsing on high tree
leaves. The exercise
of stretching up to
the leaves altered the
neck and legs, and
their offspring
inherited these
A lizard that
didn’t use its
legs would
eventually evolve
into a snake
without legs.
Lamarck’s Theory was
proven to be wrong!
We now know that features gained
during life are not passed onto
Darwin's Theory of Evolution by
Natural Selection
1. Variation exists among individuals in a species.
2. Individuals of species will compete for
resources (food and space)
3. Some competition would lead to the death of
some individuals while others would survive
4. Individuals that had advantageous variations
are more likely to survive and reproduce.
This process he describes came to be known as
Natural Selection
The favorable variations are called Adaptations
Darwin’s observations
of the finches on the
Galapagos island led
to the conclusion that
all the finches had a
common ancestor.
The shape of the
beaks were
adaptations for eating
a particular type of
Evidence for Evolution
1. Evidence from fossils
 If today's species came from ancient species,
the we should be able to find remains of those
species that no longer exist.
 We have tons of fossils of creatures that no
longer exist but bear striking resemblance to
creatures that do exist today.
 Carbon dating--gives an age of a sample based
on the amount of radioactive carbon in a
 Fossil record--creates a geologic time scale.
2. Evidence from Living Organisms
 Evidence of Common Ancestry
 Homologous Structures
 Vestigial Organs
 Cell and DNA
 Embryonic development
 Observation of species change
Evidence of Common Ancestry -Hawaiian Honeycreeper
Homologous Structures-A body part
with the same basic structure and embryonic
origin as that of another organism, though not
necessarily sharing the same function
Vestigial Organs--seemingly
functionless parts
Cell and DNA evidence
All living things are
made of cells which
have similar
Closely related
species are more
similar in their DNA
sequences than
distantly related
Embryonic development--Embryos of
different species develop almost identically
Observation of species change
(wolves/dogs, peppered moths)
Examples of Evolution
Industrial Melanism (Kettlewell's moths)
Dog breeds
Viruses & Vaccines
Bacteria & Antibiotics
Elephant Tusks