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Mechanisms of Evolution
P. 105
EQ: How does evolution happen?
Natural Selection
Genetic Drift
Gene Flow
Mutation
Recombination
Natural Selection
• Process by which random evolutionary changes are selected for by
nature in a consistent, orderly, non-random way
• Organisms best adapted to their environment have a better chance of
surviving and reproducing
Produces changes
in
POPULATIONS,
not individuals
Natural Selection
• Organisms with traits that are better
suited for a specific environment are
called the “fittest” because their traits
are best fit for their environment
• Because their traits are best suited for
their environment, the most fit
individuals will tend to survive more
often than others with less-desirable
traits for their environment
• Because they are more likely to survive,
they are more likely to reproduce a lot
(live longer)
• This which will pass their better–suited
traits on to future generations
Natural Selection
Elements of natural selection:
• inherited variation
• production of large # of offspring that
won’t all survive & finite supply of
environmental resources result in
competition
• Adaptation
• Descent with modification occurs over
time
“survival of the fittest”
A trait that helps an organism survive and
reproduce, and can be passed down to it’s
offspring, is called an adaptation.
Who will survive? Why?
Predict the amount (%) of light and dark
individuals in the moth population.
Industrial Revolution happens…
Pollution was sent into the
atmosphere. This killed the
lichen that lived on the tree
trunks. Soot also collected on the
tree trunks.
These 2 events caused the tree
trunks to darken.
Who will survive? Why?
How did you do??
Before the Industrial Revolution,
about 99% of the moths were
light.
In just 50 years after the
Industrial Revolution began,
98% of the moths were dark.
Predict the amount (%) of light
and dark individuals in the moth
population.
Explain why this happened. Your
answer should include a
discussion of predation,
survival, and inherited traits.
Speciation
• 2 species arise from one (wolf → dogs)
• Requires Reproductive Isolation
• Geographic – physically separated
• Sexual Selection Differences – different times/rituals
• Anatomical – they have to fit (think about a mouse &
elephant…)
• Allopatric Speciation - occurs when 2 or more
populations of a species are geographically
isolated from each other
• Allele frequencies in these populations change
• Members of each population become so different that
they can no longer reproduce
• Adaptive Radiation - when multiple species have
a common ancestor (ex: Darwin’s Finches)
Natural Selection
Domesticating dogs – wild dogs were trained by man and bred (artificial
selection) for desired traits. After a few generations of this, the wild dogs
were not able to breed with the domesticated dogs – this means the
domesticated dogs are a new species