Transcript Natural Selection PPT

WHAT CAUSES
EVOLUTION TO OCCUR?
DARWIN’S MECHANISM:
THE THEORY OF
NATURAL SELECTION
NATURAL SELECTION
• DEFINITION:
– the process by which organisms that are better suited to
an environment survive and reproduce in greater number
than those less suited.
• What is the KEY to natural selection?
• The environment
• “Survival of the Fittest”
• (But what is fit????)
• Categorized into 5 Steps
STEP 1: Overproduction
• All species over reproduce creating a population with
variation in the gene pool.
STEP 2: Inherited Variation
Variation (varieties) within a species come from 2 places:
MUTATIONS of the gene code
RANDOM MATING- mixing of genes in the
population (no inbreeding). Child looks similar to
but not identical to parents.
A change in the gene for feather color creates different
looking variations of a birds population
VARIATIONS IN BIRD COLOR:
• Most birds are born with traits (genes) for being bluegreen in color.
• Occasionally some birds are born with traits that make
them more green.
• Occasionally some birds are born with traits that make
them more blue.
STEP 3: Struggle to Survive
Members of the same species compete for
resources such as food, shelter, and
mates. Those better suited to meeting
these needs will survive.
The birds face the challenge of blending in to survive.
STEP 3: Struggle to Survive
Ugh!, so
full…
Not all members of the species will
survive this competition. Only
some will survive and have the
opportunity to pass on their
successful genes.
Since blue-green birds
stand out more in the
habitat than green birds,
more blue-green birds are
eaten
EEP
!
STEP 4: Successful Reproduction
Favorable traits are passed to the next generation.
Now, more members of the population are being
born with the successful variation than those with
the less suited trait.
Now more green chicks than blue/ blue-green are being born.
STEP 5: Adaptation of the Species
?
(Not included in the textbook)
Adaptation – process by which a species
becomes better suited to its
environment.
Hee, hee…
NATURAL SELECTION
EXAMPLES
•
Giraffe’s long neck
(see old textbook pg 187)
•
Peppered Moth
•
Ivory tusks of African
elephant (textbook pg 122)
NATURAL SELECTION
EXAMPLES
Antibiotics vs. Bacteria
Salmonella (bacteria that
causes food poisoning)
vs
Salmonycin antibiotic
(fights against Salmonella
bacteria)
Darwin’s
Finches
Examples of Adaptations
flounder
lichen katydid
Camouflage:
Mimicry:
monarch butterfly (left); viceroy butterfly (right)
coral snakes "Red and yellow, kill a
fellow; red and black, venom lack
DEVELOPMENT OF NEW SPECIES?
SPECIES: a group of organisms that can interbreed and produce fertile
offspring.
Steps to a NEW SPECIES
1. Separation: part of a population becomes isolated from the rest.
2. Adaptation: Natural selection constantly improves the fit
between species & environment. Populations diverge.
3. Differences accumulate creating ecological races.
4. Division: Enough differences create a NEW SPECIES.
DIVERGENCE: the accumulation of differences between populations
or species
ECOLOGICAL RACE: populations of the same species that differ
genetically because they have adapted to different conditions
At what pace does evolution occur?
GRADUALISM: states that evolution
occurs slowly over time and
includes many transitions
PUNCTUATED EQUILIBRIUM:
states that evolution occurs in short
bursts followed by long periods of
stasis (no evolving)
Discussion Questions
• According to Natural Selection, explain
why human overpopulation exists?
• Are humans evolving?