2/1/2014
Who is Charles Darwin?
Charles Darwin and
Natural Selection
Date: _________
• Began the voyage of the Beagle in 1831
– Collected fossils and observed many different types
of wildlife to and from the Galapagos islands
• 1836: came up with the theory of natural
selection, returned to England
• 1859: joint publication of the same theory
with Alfred Russel Wallace
– Book was titled On the Origin
of the Species
NO!
So did he really say that…?
• Humans did not come from monkeys,
nor did we come from chimps or any
other primate.
• We share common ancestors.
• Well, what’s the difference?
– We did not come
from primates
because primates are
still here.
– It works something
like this…
What is Evolution?
• It describes all of the changes that
have transformed life on Earth from its
earliest beginnings to what we see in
the world today.
• It’s a BIG DEAL – probably the biggest
thing about
biology!
• It’s tied in with
EVERYTHING ELSE
we’ve talked about!
Wait…there are types?
• Microevolution
– Small-scale evolution
that only affects a
single population
• Macroevolution
– Large-scale evolution
that affects the entire
species across
multiple populations
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2/1/2014
Evolution by Natural Selection
• Natural selection occurs because
individuals in a population have
different traits that allow them to
survive in the environment more
efficiently than others without these
traits.
– Results in changes in
inherited traits of a
population over time.
– These changes increase a
species’ fitness in its
environment.
Overproduction of Offspring
• How can it lead to natural
selection?
– If a population can have many
offspring, it raises the chance that
some will survive.
• The bad news:
– It can increase
competition for
resources.
Four Principles of Natural Selection
•
•
•
•
Overproduction of offspring
Variation
Adaptation
Descent with modification
Variation
• What kind of variation exists in this room
right now?
– All kinds! An organism’s phenotype may
influence its ability to find, obtain, or use
resources like food, water,
shelter, and oxygen – it may
even affect the ability to
reproduce!
• Phenotypic variation is
controlled by the organism’s
genotype and the
environment.
– Bad phenotype = death 
Adaptation
• Adaptation increases the frequency of a
particular structure, process, or behavior; it
makes the organism able to better survive
and reproduce.
– Good adaptations are passed on while bad
adaptations probably won’t be.
– This leads to a change in the gene pool over time.
• And just when you may have forgotten about
him…
– Fitness is used to measure how successful a trait is
in an environment based on how well it contributes
to reproduction.
Descent with Modification
• When the environment changes, natural
selection can shape new populations with new
phenotypes adapted to new conditions.
• Natural selection can produce
populations with different
structures or that live in
different habitats from their
ancestors – descent with
modification!
• More individuals will have
successful traits in later
generations as long as those
traits help the organism survive.
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2/1/2014
But Wait…There’s More!
• What types of organisms pass on
genetic information to offspring
through reproduction?
– All of them!
• What are the types of reproduction?
– Sexual reproduction
– Asexual reproduction
“I’m simply saying that life…finds a way.”
What’s the Difference?
• Sexual reproduction uses meiosis to
create gametes. Fertilization results in
the embryo receiving alleles from each
parent for every trait, and the individual
expresses a combination of
traits.
– Genetic variability is also a
result of…
• Asexual reproduction involves only one
parent producing offspring that are
basically genetically identical to the
parent.
– Occurs via binary fission (single-celled
organisms) or mitosis (multicellular
organisms)
– Genetic variability
only occurs via
• Mutations in the DNA
passed from parent to
offspring
• Gene shuffling
• Crossing over
• Mutations
Which one is better?
SEXUAL
Lower reproduction Methods of
rate
reproduction
Fewer offspring are
produced at a time
Genetic
Offspring vary greatly variability
from one another
ASEXUAL
Higher reproduction
rate
Many offspring are
produced at a time
Offspring are
genetically identical
An organism that can reproduce both
sexually AND asexually have a great adaptive
advantage for survival!
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