Download Natural Selection

Name _________________________________________________
Date _____________________
Period _________
Natural Selection (Darwin’s Mechanism)
Natural Selection – 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? _____________________________________
Steps of Natural Selection
1. Overproduction—All species over reproduce creating a population with many __________ (alleles)
–
the total of all _________ (or variations) in the population is called a _______________
2. Inherited Variation—______________ within a population come from _______________ &
__________ ____________ changing the population’s gene pool.
3. Struggle to Survive—Organisms ___________ for resources such as food, shelter, and mates.
Those _____________________ to meeting these needs will ____________. Not all members of the
species will survive this competition. Only some will survive and have the opportunity
______________________ their ______________________.
4. Successful Reproduction—Successful _____________ are passed to the next ________________.
Now, more members of the population are being born with the ______________ variation than those
with the __________________ trait.
5. Adaptation of the Species—process by which a species becomes better __________ to its
environment.
Examples of Natural Selection
1.
2.
3.
Discussion Questions:
1. According to Natural Selection, explain why human over population exists?
2. Is the human species still evolving? Explain.
Name _________________________________________________
Date _____________________
Period _________
Speciation (Steps to a New Species)
Speciation – The formation of a new species by the change of allele frequency (traits) due to natural selection.
Species – a group of organisms that can interbreed and produce fertile offspring.
Steps of Speciation
1. Separation / Isolation:
What could cause separation?
2. Adaptation: Natural selection improves the fit between ____________ & ____________________
created from ___________ in the gene pool.
3. Divergence: _________________ in the gene pool _______________ between populations.
Eventually this could lead to a _____________________.
Examples of Speciation
1.
2.
3.
Factors Contributing to Speciation
1. Isolating Mechanisms - Genetic differences __________ ____________ among related
species, helping to cause speciation. This can happen before or after mating.
2. Genetic Drift - A loss of ____________ ____________ (alleles) brought about by
___________. Usually in small populations.
3. Founders Effect - A loss of genetic variation from a ________ ____________established and
genetically _____________ from a larger population (usually contains some rare variations
(alleles) making the gene pool different from the original). Example:
4. Migration - Gene pools of smaller populations change from the ____________ & ___________
of individuals from _____________ populations with unique variations (alleles)
Pace of Evolution
(1) Gradualism -
(2) Punctuated Equilibrium -