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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
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
Marine Iguana
Land Iguana
Darwin’s Postulates
Variation within populations.
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 viable
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.
Can a fish species willfully
grow limbs and fingers if they
are needed to crawl out of the
water onto dry land?
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
Activity:
• Choose an online natural selection simulation.
• Work through the simulation and discuss the
strengths and weaknesses of the simulation with
regard to modeling natural selection.
• In your own words, explain how a new species forms.
http://www.techapps.net/interactives/pepperMoths.swf
(requires flash)
http://www.sciencechannel.com/games-andinteractives/charles-darwin-game.htm
http://phet.colorado.edu/en/simulation/natural-selection
(requires shockwave)