Natural Selection
4.1.2 OUTLINE THE MECHANISM OF
NATURAL SELECTION AS A POSSIBLE
DRIVING FORCE FOR SPECIATION.
What is evolution?
What does it mean to you?
Do you think it happens?
Evidence? (for or against)
http://evolution.berkeley.edu/evolibrary/article/evo_25
DEFINITIONS:
Evolution are the changes in the gene pool of a population over
time.
Natural selection process by which individuals that are better
suited to their environment survive and reproduce most
successfully.
Adaptation is an inherited characteristic that increases an
organism’s chance of survival.
Darwin and Evolution
1809-1882
Sailed around world 1831-1836
Darwin
Wolf
Pinta
Marchena
Genovesa
Santiago
Bartolomé
Fernandia
Råbida
Pin zon
Seymour
Baltra
Santa Cruz
EQUATOR
Santa Fe
Tortuga
Isabela
San Cristobal
Española
Floreana
Galåpagos
Islands
Each island had its own
type of tortoises and birds
Through his travels he
found that species diversity
was much greater than
previously known.
Marine Iguana
Land Iguana
His observations led
to the development
of the theory of
evolution.
What is a Theory?
 A well tested idea
that explains an
observed phenomena
 Supported by
multiple sources of
evidence
Darwin’s Postulates
Populations have natural Variation
Overproduction of offspring.
Struggle for existence.
Unequal survival and reproduction rates. (Those with
traits more likely to help them survive will pass traits
to their offspring)
What is a species?
A group of individual organisms that are
capable of reproducing and produce fertile
offspring.
When organisms can no longer reproduce or
do not produce viable offspring then they
are no longer the same species.
KONA
FINCH
extinct
KAUAI AKIALAOA
AMAKIHI
LAYSAN
FINCH
IIWI
AKIAPOLAAU
APAPANE
MAUI
PARROTBILL
fruit and seed eaters
insect and nectar eaters
FOUNDER SPECIES
Based on his observations, Darwin proposed that EVOLUTION
occurs by NATURAL SELECTION.
Population of organisms
Overproduction of
offspring
Limited resources
leads to a struggle for
survival between
offspring.
Population changes
over time.
Mutations & Sexual
reproduction
produces variations
among offspring.
Survivors reproduce
more successfully.
The Genetic Makeup of a Population Can Change
• Populations evolve by becoming
genetically different
• Genetic variations
• First step in biological evolution
• Occurs through mutations in
reproductive cells
• Mutations in other cells can
happen , but only reproductive
cell mutations are passed on
• Sometimes a mutation can result
in a new genetic trait that gives it
a better chance to survive,
sometimes not.
Individuals in Populations with Beneficial
Genetic Traits Can Leave More Offspring
• Natural selection: acts on individuals
• Second step in biological evolution
• Adaptation may lead to differential reproduction
• Genetic resistance in bacteria, cockroaches
• When environmental conditions change, populations
• Adapt
• Migrate
• Become extinct
A group of bacteria,
including genetically
resistant ones, are
exposed to an
antibiotic
Normal
bacterium
Resistant
bacterium
Most of the normal
bacteria die
The genetically
resistant bacteria
start multiplying
Eventually the
resistant strain
replaces the strain
affected by
the antibiotic
Evidence Supporting Evolution
Fossil Record
Evidence Supporting Evolution
Homologous Structures
Evidence Supporting Evolution
Vestigial Structures
Evidence Supporting Evolution
Embryo Development
Opposing Theory at the Time
Lamark: Theory of Acquired Traits
 Lamark believed that
organisms acquired
traits by using their
bodies in new ways
 These new
characteristics were
passed to offspring
 Why was
Lamark’s theory
refuted???
Can a fish species willfully
grow limbs and fingers if they
are needed to crawl out of the
water onto dry land?
Origin of Species
 Darwin published his book The Origin
of Species in 1859
 His findings are still supported today
by further evidence and the scientific
community.
Activity:
• Choose two online natural selection simulations.
• Work through the simulation and discuss the
strengths and weaknesses of the simulation with
regard to modeling natural selection.
• Which simulation do you believe does a better job
modeling natural selection? Justify your answer.
• In your own words, explain how a new species forms.
http://phet.colorado.edu/en/simulation/natural-selection (requires shockwave)
http://sepuplhs.org/high/sgi/teachers/evolution_act11_sim.html
http://biologyinmotion.com/evol/
http://www.techapps.net/interactives/pepperMoths.swf (requires flash)
http://www.sciencechannel.com/games-and-interactives/charles-darwin-game.htm