Evolution and Natural
Selection
How species change over time
S
Evolution and Natural Selection
S Genetic variations are passed on through
reproduction
S Evidence for evolution illustrates how
organisms are related
S Natural selection leads to evolution
S Our understanding of evolution has changed
over time
Evolution
S The theory that organisms
today developed from more
simple life forms and have
changed (evolved) over time.
Natural Selection
S The theory that states that
those organisms best adapted
to their environment have a
better chance of surviving
and reproducing.
What was Darwin’s hypothesis?
S Darwin hypothesized
that organisms had a
common ancestor,
but had adapted to
their particular
environments and
changed over time.
S Darwin published
his
research in 1859
Natural Selection
S For natural selection to occur, there
must be at least two varieties of a
species.
S For example: the peppered moth
Peppered Moths
S At the beginning of the Industrial
Revolution in England, coal burning
produced soot that covered the countryside
in many areas
What do you think happened?
Evolution/Natural Selection
S White moths became easier
to see, while the black
moths became harder to
see. The black moths were
more likely to survive and
pass on the gene for dark
color to their offspring.
S Over time, the black moths
have become more
common.
Evidence for Evolution:
Common Ancestry
S Common Ancestry: If species evolved from a
common ancestor, then they should share common
anatomical traits
S Hawaiian Honeycreeper: family of
birds in Hawaii that have similar
skeletons and muscles, indicating
they are closely related.
S Over time, their common ancestor evolved
into several species, each with a specialized bill
for eating certain foods. Just like Darwin’s finches
on the Galapagos!
Evidence for Evolution:
Homologous Structures
S If animals evolved from
a common ancestor,
then they should share
common structures –
and they do!
S These are called
homologous structures
Evidence for Evolution
Embryo Development
S What do you notice? List 2 observations
Evidence for Evolution:
Vestigial Organs
S Some organisms have structures or
organs that no longer have a useful
function.
S These structures or organs may have
been useful to the ancestors of a
species, but over time have evolved
into what we term vestigial organs.
Examples of Vestigial Organs
S
Kiwi (flightless bird)
S
Whales (hind leg bones)
S
Humans (tailbone, appendix)
Evidence for Evolution
Fossils
S Fossils provide a look
into the past
S Scientists can trace
how
a species has evolved
by studying fossils
Wrap Up the Evidence
S Common Ancestry
S Homologous Structures
S Vestigial Organs
S Embryonic Development
S Fossils
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?
REMEMBER: Natural Selection Rests on 4 Premises:
1) There is variation in the traits of
individuals within a population
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:
2) There is differential survival and
reproduction, i.e., some individuals
survive and reproduce, some
don’t
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X
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REMEMBER: Natural Selection Rests on 4 Premises:
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.
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X
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X
X
X
X
X
X
X
X
X
X
X
X X
X X
X
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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!
Discussion Topic
S Echidna and Platypus belong in the animal kingdom and in
the Phylum Mammalia, though both Echidna and Platypus
have characteristics that can be categorized in the mammal,
reptile or avian phylum. If you were the scientist to change
the taxonomy, would you change their classification or keep
it the same? Give evidence and logical response.
Activity
S Go to the following website and answer the worksheet.
S http://phet.colorado.edu/en/simulation/natural-selection
S You will need to download Java to play this.