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Ch 14 - Evolution (2)
How change occurs
History:
Jean Baptiste de
Lamark first noticed
that living things
have changed over
time.
 He proposed an
evolutionary theory
based on 3 reasons
for change.

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1. An INNATE urge to
BETTER
THEMSELVES.
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2. “Use and Disuse” CHARACTERISTICS that
were in constant use
developed (were AQUIRED)
and those that were not used
were LOST.
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3. Inherited
Acquired traits
 - traits developed by
extra “use” were
then passed on to
the OFFSPRING
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Lamarck himself
conducted experiments
where he cut the tails
off of mice hoping to
eventually produce a
generation without any
tails. He was not
amused, the joke goes,
when a colleague
noted that the some
doctors had been
performing that same
experiment on infant
boys for thousands of
years.
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Unfortunately,
Lamarck was
INCORRECT
on all three
points, and his
evolutionary
theory was
DISPROVED.
Charles DARWIN
first published
the more modern
theory of
EVOLUTION.
 His ideas were
INFLUENCED by
several other
scientists’ work:

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http://evolution.berkeley.edu/evolibrary/home.php
http://evolution.berkeley.edu/evolibrary/home.php
www.darwinday.org/englishL/life/beagle.html
www.darwinday.org/englishL/life/beagle.ht
Used by permission of Darwin Day
Celebration (at DarwinDay.org), 2006
I have called this principle, by which
each slight variation, if useful, is preserved,
by the term Natural Selection.
—Charles Darwin from "The Origin of Species"
http://evolution.berkeley.edu/evolibrary/home.php
Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.



1. Charles
LYELL
A GEOLOGIST who
published “PRINCIPLES OF
GEOLOGY “
In this book, Lyell proposed
the NEW idea that the Earth
was VERY OLD and that it
had CHANGED greatly over
time. Darwin used this
information to formulate his
THEORY.
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2. Farmers and
ARTIFICIAL selection.
Through SELECTIVE
breeding, farmers were
able to change their
crops and livestock.
Darwin first realised
that natural
VARIATION in the
species was the basis for
change.
ARTIFICIAL SELECTION
Teosinte (left) and its
modern descendent,
corn, a product of
artificial selection

Individuals with UNDESIRABLE traits were not allowed to
BREED, so their specific combination of genes did not get
PASSED ON. Those that had DESIRABLE traits were
breed - therefore the desirable traits were INHERITED by their
offspring. Darwin termed this process ARTIFICIAL
SELECTION.

Link for artificial
selection super cow
http://www.youtube.
com/watch?v=Nmkj
5gq1cQU:
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3. Thomas Malthus
 An ECONOMIST.
 First noted that the

BIRTHRATE was
greater than the
DEATHRATE in
humans. He
hypothesized that the
only things that would
stop the
EXPONENTIAL
growth of humans
would be FAMINE,
DISEASE AND WAR.
They called this the
MALTHUSIAN
DOCTRINE.
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Darwin noticed that other species also have
LIMITING FACTORS that control their
population. He wondered what determined which
individuals would SURVIVE AND REPRODUCE
and which would DIE.
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14.2 - Evolution by
Natural Selection

Using these
concepts, Darwin
developed the idea
of NATURAL
SELECTION.
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“Survival of the
Fittest”
If you are “FIT” you
live and reproduce.
 If you are not as
“FIT”, you do not live
or you do not
reproduce AS
WELL.

Peppered Moth Example

Before Industrial
revolution in
England

After Industrial
revolution
 (they started burning
coal which turned all
the tree’s black from
the soot)
NATURAL SELECTION
SCENARIO
1. There is variation in traits
2. There is environmental pressure (birds
Like the green ones!)
3. There is heredity
4. End result
Variation + differential feeding + Heredity = Natural selection
Natural selection
14.3 - Genetics and
Evolutionary Theory
MUTATIONS:
The RAW MATERIAL for
natural variation.
Changes in our GENES
create the initial
VARIATION in species.
(don’t forget to study DNA
STRUCTURE,
“de-coding DNA” and
MUTATIONS in DNA)
Gene Pool

Total # OF GENES
genes in a
POPULATION at
any one time
SEXUAL
REPRODUCTION
continues to mix up
the gene
combinations in
GENE POOLs, so
there is even more
NATURAL VARIATION
in the species.
Evolution: any change in the
relative frequencies of alleles in the
gene pool of a population.
Before
grassmouse population
After sodinwas
laidyard
down
E.g.
Field
back
Sandy brown
45
Sandy brown
10
Black
4
Black
4
Specked brown
29
Specked brown
29
WHAT HAPPENED?
The specked brown mice had an advantage over the other colours of mice
after the sod was laid.
WHY?
Though the specked brown population did not increase, the number of the
“specked brown” allele changed as compared to the others.
The RELATIVE FREQUENCY of the “specked brown” allele changed.
Therefore, according to the new definition, evolution has occurred.
WHICH ONE IS AN EXAMPLE
OF EVOLUTION?
Beetles on a diet
There was a year or two of drought, there were
less plants that these beetles can eat. All the beetles
have the same chance of survival and reproduction,
but because of food restrictions the beetles are a little
smaller than the previous generation.
Beetles of a different colour
90% of the beetles in the population have the gene for green coloration.
A few generations later 70% of the population have the gene for brown coloration.
14.4 Notes: SPECIATION
how new SPECIES develops from old ones
 usually due to ISOLATION. (they aren’t able to
get to each other, so they are not able to
BREED. )

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GEOGRAPHIC ISOLATION often leads to
REPRODUCTIVE isolation; they are no longer able
to produce FERTILE offspring.
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This might even be
due to differences in
MATING rituals –
they might not
recognize the “signs”!

BIRD OF PARADISE
MATING RITUALS FROM PLANET
EARTH
SEXY? --->
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 Once reproductive
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ISOLATION occurs,
the DIFFERENCES
between the two new
species often increases.
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5 Steps to SPECIATION

1. FOUNDING
Fathers and
Mothers.
 An original
POPULATION is
established in it’s
environment and fills
a particular NICHE.
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2. Separation of the Populations.
(=GEOGRAPHIC
ISOLATION)
- a few individuals
move away from the
original
POPULATION and
don’t RETURN.
-
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3. Changes in the
GENE POOL
 the
two locations
have different
environments.
The populations
slowly “ADAPT”
to the
environment.
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 **Remember
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that adaptation
does not occur because the
populations WANT to change.
 Change occurs because
NATURAL VARIATION is
present in the population.
 Some traits will give an
individual an ADVANTAGE
over others, making them more
FIT to the ENVIRONMENT.
 Greater FITNESS means more
OFFSPRING. Those genes will
be passed on, while those that
are not as FIT to the
environment will not be
PASSED ON..***
4. REPRODUCTIVE Isolation
 The
changes in the GENE
POOL make it impossible
for them to BREED.
 They might not
RECOGNIZE each other
any more, or they might
have different MATING
rituals. Their
“REPRODUCTIVE
MACHINERY” might not
fit together anymore!
There could be many
reasons why they can no
longer produce FERTILE
offspring.
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A niche refers to the “PROFESSION” of the species,
as well as the RESOURSES the species utilizes for
LIVING.
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If, after SPECIATION has
occurred, the two
populations still fill the
same NICHE, they will be
in direct COMPETITION
with each other for
RESOURSES when they
try to share the same
space.
One species may
OUTCOMPETE the other
and cause its
EXTINCTION. However,
the competition may
cause the species to
further ADAPT to fill
separate NICHES so that
they might live in
HARMONY!
How do we define a SPECIES?

They look different, but they can interbreed, so
they are still the same species
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The Western meadowlark (left) and the Eastern
meadowlark (right) appear to be identical, and
their ranges overlap, but their distinct songs
prevent interbreeding.
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But these two ants ARE the same
species - they are sisters, actually!
(they have different jobs)
Adaptive Radiation
(DIVERGENT Evolution) vs.
CONVERGENT Evolution
ADAPTIVE
Radiation – many
different species
evolve from one
COMMON
ANCESTOR.
 (like the SPOKES
on a wheel that
RADIATE from
the centre)
ONVERGENT Evolution

Many different
species will evolve
with similar
SOLUTIONS to
environmental
CHALLENGES
.
.

Different sorts of anteaters
 Though not closely related, they all
INDEPENDENTLY evolved the "tools"
necessary to subsist on an ant diet: a long,
sticky tongue, few teeth, a rugged stomach,
and large salivary glands.

However, unless the
species evolved from a
common ANCESTOR, the
structures formed are
often very DIFFERENT in
form. Convergent
evolution produces
ANALOGOUS structures.
Eg. Birds, BATS, squirrels, flying fish and INSECTS all
have
 “WINGS” so that they can FLY, but the INTERNAL
structure of the wings is very different.

14.5 – Genetic DRIFT
Occasionally, NATURAL SELECTION is not
responsible for evolutionary changes.
Genetic drift is known as evolution “BY
CHANCE.”

There are some
traits that have
evolved despite
the fact that they
do not give an
ADVANTAGE
over another.

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
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Example:
Indian Rhinoceros – ONE
horn
African Rhinoceros – TWO
horns
– but there is no
ADVANTAGE to having
a second horn, or to having
only one.
In many cases,
genetic drift occurs
due to a NATURAL
DISASTER
 Example: A FLOOD
wipes out the most
of the mouse
population in that
area.



By chance, a few of the
black mice were AWAY
FROM THE AREA.
When the water drained
away, they were left to
REPRODUCE. Now the
area has a mostly BLACK
mouse population. It
wasn’t that the black color
was an ADVANTAGEOUS
trait; the black mice were
just LUCKY!
GRADUALISM vs Punctuated
EQUILIBRIUM
Darwin’s theory of evolution supports a
GRADUALISM theory of change. That is, Darwin
believed that species change SLOWLY AND
STEADILY over a very long period of time, and
that they are always changing due to
ENVIRONMENTAL PRESSURES.

However, the FOSSIL RECORD seems to suggest that there
were species that experienced PERIODS
of change
followed by periods of NO CHANGE AT ALL..

It has been suggested that species experience a
type of EQUILIBRIUM with the environment
until something in the environment CHANGES.
Then the species have to ADAPT, so they
undergo RAPID PERIODS of evolution. These
periods are followed by equilibrium, and the
CYCLE REPEATS. This relatively new and
controversial theory is called PUNCTUATED
EQUILIBRIUM.
# of
species
# of
species
Time
Time
Living Fossils

Ex: the horseshoe
crab Limulus. This
species of crab has
not changed in
hundreds of millions
of years. Could it
really have such a
great design that it
didn’t need to
CHANGE?