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Natural
Selection
Survival of the Fittest?
 Is this what Darwin meant?
Natural Selection
 The process by which organisms with
favorable traits survive and reproduce
at a higher rate than organisms without
the favorable trait
Natural Selection
 Organisms  Better able to survive and reproduce
in an environment
 More likely to pass their traits on to
future generations
 Traits improve chances of survival or
reproduction
 Likely to accumulate in a population after
several generations
 Traits are “selected”
Natural Selection in Four Steps
 Overproduction
 Genetic Variation
 Struggle to Survive
 Successful Reproduction
Overproduction
 More
individuals
are born
than will
become
adults.
Genetic Variation
 Individuals
 Not exactly the same
 Have own set of traits
(size, color and the
ability to find food)
 Some traits more likely
to survive and reproduce
 Other traits less likely
for survival and
reproduction
Struggle to Survive
 Environment
 Not able to support
all of the individuals
born
 Individuals
 Killed by other
organisms
 Do not find mates
 Only some will
become adults and
reproduce
Successful Reproduction
 Individuals and Their
Environment
 Well Adapted
 More likely to survive
 More likely to
reproduce
 Traits likely to be
selected
 Not Well Adapted
 More likely to die
early
 Have few offspring
 Traits less likely to be
selected
Survival of the Fittest
 Key to Natural Selection – Heredity
 Traits passed from one generation to the
next
 No reproduction – genes will not be passed
on
 Characteristics
 Survival vs. Reproduction
 Peacock’s bright feathers
 Flower’s color
Natural Selection in Action
 Population
 Changes in response to its
environment
 Tends to be well adapted to its
environment
 Environment changes too quickly
 Some organisms may not survive
 Only organisms with certain traits are
able to survive and reproduce in the
new environment
Natural Selection in Action
 Examples
 Insecticide Resistance
 Adaptation to Hunting
 Industrial Melanism
 Butterfly Story
Insecticide Resistance
Adaptation to Hunting
 Tusks of Male African Elephant
 1930 – 99% born with tusks
 Present – as few as 85% have tusks
 Males with tusks killed therefore could
not reproduce
 Males without tusks able to reproduce
 If this trend continues tuskless elephants
will outnumber elephants with tusks
 Males did not lose tusks, tuskless
elephants were able to pass on their traits
Industrial Melanism
How has predation
influenced evolution?
 Adaptations to avoid
being eaten:
 Spines (cactii, porcupines)
 Hard shells (clams, turtles)
 Toxins (milkweeds, dart
frogs)
 Bad taste (monarchs)
 Camouflage
 Mimicry
 Aposematic colors
Quiz
 Adaptation and Survival
 How does this characteristic help with survival or
successful reproduction
 Stripes on a tiger –
 Song of a bird –
 Ears of an elephant –
 Poison of a rattle snake –
 Glow of a firefly –
 Antler of a male deer –
 Bright flowers of a rose –
Quiz
 Adaptation and Survival
 How does this characteristic help with survival or
successful reproduction
 Stripes on a tiger Camouflage for hunting
 Song of a bird –
Attracts mate/defends
territory
Quiz
 Ears of an elephant –
Prevent overheating
 Poison of a rattle snake –
 Capture of prey, protection
from predators
Quiz
 Glow of a firefly –
Attracts mate
 Antler of a male deer –
 Defends right to mate
Quiz
Bright flowers of a rose –
 Attract pollinators
VOCABULARY REVIEW
 EVOLUTION – CHANGE OVER TIME
 NATURAL SELECTION - INDIVIDUALS
BETTER ADAPTED TO THE
ENVIRONMENT ARE ABLE TO
SURVIVE & REPRODUCE.
 A.K.A. “SURVIVAL OF THE FITTEST”
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
mutation!
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
Generation 3: 0.76 not resistant
0.24 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
Generation 3: 0.76 not resistant
0.24 resistant
Generation 4: 0.12 not resistant
0.88 resistant
3 ISOLATING MECHANISMS……..
 BEHAVIORAL ISOLATION- CAPABLE OF
BREEDING BUT HAVE DIFFERENCES IN
COURTSHIP RITUALS (EX.
MEADOWLARKS)
 GEOGRAPHICAL ISOLATION –
SEPARATED BY GEOGRAPHIC BARRIERS
LIKE RIVERS, MOUNTAINS, OR BODIES
OF WATER (EX. SQUIRREL)
 TEMPORAL ISOLATION – 2 OR MORE
SPECIES REPRODUCE AT DIFFERENT
TIMES.
Table 23.1a
3.How did tortoises and birds
differ among the islands of
the Galapagos?
 Each island
had its own
type of
tortoises
and birds
that were
clearly
different
from other
islands
Galapagos
Turtles
5. Geologists:
Hutton and Lyell
Fundamentalists said that the
earth was around 6000 years
old
Hutton and Lyell argued that
the earth is many millions of
years old b/c
 layers of rock take time to
form
 processes such as
volcanoes and earthquakes
shaped the earth and still
occur today
Lamark
Theory of acquired
characteristics

Lamark said
organisms acquired
traits by using their
bodies in new ways

These new
characteristics were
passed to offspring

Lamark was totally
wrong!
9. Artificial Selection
 nature provides variation, humans select
variations that are useful.
 Example - a farmer breeds only his best
livestock
10. Natural
Selection
 The traits that
help an organism
survive in a
particular
environment are
“selected” in
natural selection
11. Natural Selection and
Species Fitness
 Overtime, natural selection results in
changes in the inherited
characteristics of a population.
 These changes increase a species
fitness (survival rate)
Descent with Modification
 Each living
species has
descended
with changes
from other
species over
time
Summary of Darwin’s Theory
1. Organisms differ; variation is inherited
2. Organisms produce more offspring than
survive
3. Organisms compete for resources
4. Organisms with advantages survive to pass
those advantages to their children
5. Species alive today are descended with
modifications from common ancestors
13. Evidence of Evolution
1. Fossil Record
2. Geographic Distribution of Living
Species
3. Homologous Body structures
4. Similarities in Embryology
Evidence of
Evolution
Fossil Record provides
evidence that living
things have evolved
Fossils show the history
of life on earth and
how different groups
of organisms have
changed over time
Relative
vs.
Absolute
Dating
Relative
Dating
 Can determine a
fossil’s relative age
 Performed by
estimating fossil age
compared with that of
other fossils
 Drawbacks – provides
no info about age in
years
Absolute
dating
 Can determine the
absolute age in
numbers
 Is performed by
radioactive dating –
based on the amount
of remaining
radioactive isotopes
remain
 Drawbacks - part of the
fossil is destroyed
during the test
13. Evidence of
Evolution
2. Geographic
Distribution of Living
Species
Similar animals in
different locations
were the product of
different lines of
descent
13. Evidence of
Evolution
Turtle
Homologous Body
Structures
 Structures that have
different mature
forms but develop
from the same
embryonic tissues
Alligator
Bird
e.g. Wing of bat,
human arm, leg of
turtle
Homologous Body Structures
Vestigial Organs
 traces of homologous organs in other
species
 Organ that serves no useful function
e.g. Appendix
13. Evidence of
Evolution
Similarities in
Embryology

In their early
stages of
development,
chickens,
turtles and rats
look similar,
providing
evidence that
they shared a
common
ancestry.
Embryological development
Figure 1. Aligned DNA fragment and first
chromosome banding patterns for man
(Homo sapiens),chimpanzee (Pan
troglodytes), gorilla (Gorilla gorilla), and
orangutan (Pongo pygmaeus).
Pictures/Images
 http://www.cbs.com/primetime/survivor/
 http://www.whimsicalart.com/ProdImages/Survival.jpg
 http://www.gototem.com
 http://www.ebertfest.com/two/grave_firefli
es_bluebat.jpg
 http://www.ohec.org/photos/poster_deer.j
pg
 http://www.seniorsplace.com/shopping/jp_pfc_britereward.jpg
Bibliography
 Holt Science & Technology textbook,
Grade 7
 http://serendip.brynmawr.edu/sci_edu/wa
ldron/pdf/NaturalSelectionProtocol.pdf
 http://www.clas.ufl.edu/users/rhatch/NSFPLANS/4-1_ORIGIN.htm
 http://www.msu.edu/~vogtjeff/biology/unit
_pages/unit_outline_natural_selection_a
nd_evolution.htm
 www.switcheroozoo.com