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Natural Selection
“Survival of the fittest”
More examples of Evolution
 x 2
UNIT 3 Chapter 7: Introducing Evolution
Introducing Evolution
Birds are a diverse group of animals. Traits from beak
to colour to nutrition are adapted to the environment in
which they live and reproduce.
UNIT 3 Chapter 7: Introducing Evolution
Section 7.1
7.1 Adaptation and Variation
• Extinct species have disappeared from
Earth completely, and all species face this
• What factors explain how and why some
species survive and some do not?
– diversity of the organisms within a
– behaviour
– interactions with the
(A) Camouflage allows this stick
insect (Eurycnema goliath) to
blend in with its environment and
avoid being eaten by predators.
(B) Many owls such as this barn
owl (Tyto alba) can sneak up on
their prey because of another
adaptation: fluffy feathers make
their flight quite silent.
UNIT 3 Chapter 7: Introducing Evolution
Section 7.1
• Adaptations of structure, behaviour, or a physiological
process give some organisms a better chance of survival
than those without the adaptations *within a species
• This survival advantage allows those organisms to
reproduce and pass on their adaptations
Let’s take a look at some
adaptations that have “stuck”
Related species of insects called mantids have
diverse shapes and colors that evolved in
different environments.
Animals brought
from Europe
changed in body
size, weight and
ear size as they
adapted to the
hot, dry Australian
As its favourite
source of nectar
disappearing, the
(Hawaii) sought
nectar elsewhere
and its bill
became sharper
Marine snails
(New England)
changed its shell
shape so that it
became thicker,
likely in response
to being hunted
by crabs
Polar Bears
How are they
able to
through the
harsh winters
in the Arctic?
Venus Fly Trap
Plants have
adapted to
UNIT 3 Chapter 7: Introducing Evolution
Section 7.1
Adaptations and Survival
Adaptations occur after long periods of time – Why?
•Adaptations (changes) are the result of random,
heritable mutations in DNA that accumulate over
•Help an organism survive and reproduce
What determines if a change will stay in the
•interaction with the environment determines
whether a mutation is positive or negative for
the individual organism
UNIT 3 Chapter 7: Introducing Evolution
The variations within
a species are the
structural, functional,
or physiological
differences between
As a variation
becomes more
common, it will be
passed on to more
• Eventually, it will
be considered a
trait in the
Section 7.1
UNIT 3 Chapter 7: Introducing Evolution
Section 7.1
• A type of structural adaptation where a harmless species
physically resemble a harmful species – why?
– Predators avoid the harmless species as much as they
do the harmful one
Organisms with the structural
adaptation of mimicry, such as the
viceroy butterfly (top), have
coloration or structures that are
similar to harmful or bad-tasting
species, such as the monarch
butterfly (bottom).
UNIT 3 Chapter 7: Introducing Evolution
Section 7.1
The English Peppered Moth:
From Variation to Adaptation
The English peppered moth (Biston betularia) is an
excellent example of how the proportions of some inherited
characteristics in a population change in response to
changes in the environment. Those changes are viewed as
evolutionary adaptations.
The peppered moth has three colour variations:
• greyish-white with black dots
• black
• intermediate colour between the above
Natural Selection in Action
UNIT 3 Chapter 7: Introducing Evolution
Section 7.1
Around 1848, the black variety made up 2% of the
peppered moth population in Manchester, England.
During the next 50 years, Manchester became the site of
intense industrial development.
By 1898, 95% of the moths were black. However, the rural
areas had a lower frequency of black moths.
What could explain these trends?
UNIT 3 Chapter 7: Introducing Evolution
Section 7.1
• Before the Industrial Revolution, the bark on many trees in
Manchester was covered with light-coloured lichen
• During the Industrial Revolution, soot pollution from factories
killed the lichen and blackened the bark
• At first, greyish-white moths were camouflaged; later, black
moths were camouflaged [camouflage = protection from
• The moths that were camouflaged lived longer, were able to
reproduce, and produced more offspring with the same
UNIT 3 Chapter 7: Introducing Evolution
Section 7.1
The ratio of greyish-white-to-black moths in the
population changed over successive generations due to
an environmental change.
In the 1950s, England enacted clean-air legislation.
How might the environment have changed after the 1950s?
Predict what happened to the peppered moth population.
Natural Selection
Darwin put it best:
“Individuals having any advantage, however
slight, over others, would have the best chance of
surviving and procreating their kind”
This notion did not come to Darwin at
lightning speed! Like a good scientist, his
theory came from several observations and
Darwin’s Observations
Observation #1: Individuals within
a species vary in many ways
Individuals of a Species Vary
Darwin’s Observations
Observation #2: Some of this
variability can be inherited
Darwin’s Observations
Observation #3: Every generation
produces far more offspring than can
survive and pass on their variations
Darwin’s Observations
Observation #4: Populations of
species tend to remain stable in size
Darwin’s Inferences
Inference #1: Members of the same
species compete with each other for
Darwin’s Inferences
Inference #2: Individuals with more
favourable variations are more likely
to survive and pass them on.
Survival is not random.
Darwin’s Inferences
Inference #3: As
these individuals
proportionately more
offspring to
generations, the
favourable variations
will become more
common (i.e. natural
Darwin in 3 Points
Natural selection is differential success in
reproduction (unequal ability of individuals
to survive and reproduce)
 Natural selection occurs through an
interaction between the environment and
the variability inherent among the individual
organisms making up a population
 The product of natural selection is the
adaptation of populations of organisms to
their environment
How did Darwin do it?
Darwin was able to formulate his theory
fossil evidence,
 the ability to date rocks,
 or any knowledge/understanding of the
genetic basis of inheritance and variation!
What is the source of variation?
• This evolutionary tree of the elephant
family is based on evidence from fossils
Artificial Selection
Breeding animals and
plants for desirable
Mass production of
‘ideal’ organisms
artificially removes
unwanted traits
Examples: dogs, horses,
oil and corn
Antibiotic Resistance: Evolution
by Natural Selection
Occurs by bacteria with
specific traits that allow them
to survive exposure to drugs
and therefore thrive, reignite infections, and launch
to new hosts
Two innate characteristics
allow bacteria to evolve that
 Fast doubling time
 Ability to swap genes with
other bacteria
A demonstration….
Clover Case Study