Transcript what causes evolution to occur?

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 causes natural selection?
• Environmental Change
• “Survival of the Fittest”
• (But what is fit????)
• Categorized into 5 Steps
STEP 1: Overproduction
• All species over reproduce creating a population with many
variations.
STEP 2: Inherited Variation
Variations within a population come from mutations & random
mating.
MUTATIONS: Changes in an organisms DNA or genes
RANDOM MATING: mixing of genes through
reproduction
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
Organisms 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
Successful 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
•
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)
SPECIATION: Steps to a 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.
•
What could cause separation?
2.
Adaptation: Natural selection improves the fit between species &
environment. Populations diverge.
3.
Division: Enough differences create a NEW SPECIES.
DIVERGENCE: the accumulation of differences between populations
or species
Are these examples of species?
Example of
Speciation:
Darwin’s
Finches
(See page 124 in textbook or
article)
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?