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Evolution and Natural Selection
What Evolution is NOT
What Evolution IS
—  Change in a gene pool
over time
—  Evolution unites all fields of biology!
¡  Cell biology
¡  Genetics/DNA
¡  Ecology
¡  Biodiversity/Taxonomy
Carolus Linnaeus
—  Developed the naming
system that we use to
classify organisms today
—  He grouped organisms
with similar
characteristics together
because their
characteristic implied
they were more closely
related
Jean-Baptiste Lamarck
—  Developed the leading theory of evolution before
Darwin
—  Said that organisms acquired new characteristics
over their lifetime through use/disuse, and could
pass those new characteristics on to their offspring
Geologic Change
—  In the 1700’s scientists started to develop theories
about how the Earth had changed over time
—  These theories made Charles Darwin think about
how life had also changed over time
Catastrophism
—  Things like volcanoes and earthquakes caused mass
extinctions and developed new landforms
¡ 
George Cuvier
Gradualism
—  Changes on Earth occur in small steps over long
periods of time
¡ 
James Hutton
Uniformitarianism
—  Geologic processes add up over long periods of time
to cause great change
¡ 
Charles Lyell
Charles Darwin
—  Set sail on the HMS
Beagle in 1831
—  Recorded information
about the organisms
encountered across the
world
—  Made most of his key
observations in the
Galapagos Islands
What did Darwin observe?
—  Variations among
similar species
¡ 
Variations are differences in
the physical traits between
individuals
—  Species on each island
had differences
¡ 
He thought that maybe the
differences were a result of
different ecosystems and
conditions on each island
Adaptation
—  Because the variations
between island species
often corresponded to
their environment,
Darwin hypothesized
that the species had
adapted to their
conditions
¡ 
An adaptation is a feature
that allows an organism to
survive better in its
environment
Artificial Selection
—  Artificial Selection means
that humans choose the
traits they see as beneficial
in other organisms and
breed those organisms to
make those traits more
prominent
¡ 
People have been doing
artificial selection for
thousands of years!
—  Artificial selections leads
to evolution
Natural Selection
—  Individuals that have
inherited beneficial
adaptations produce
more offspring on
average than other
individuals
—  Natural Selection acts on
the phenotype of
populations
—  The environment acts as
a selective agent-it puts
pressure on populations
to change
Natural Selection is not always at work!
Certain conditions have to be met for natural selection
to occur in a population
—  The trait must be heritable
—  Overproduction of offspring-more babies born than
what the environment can support
—  Variation-some individuals have the trait, some don’t
—  Differential reproduction-individuals with the trait
produce more offspring than individuals without it
Survival of the Fittest
—  Fitness is a measure of how
well an individual can
survive and reproduce
relative to other
individuals
—  The “fittest” individual is
not necessarily the biggest,
smartest, or strongest!
—  Fitness depends on the
environment! If the
environment changes,
what trait are fit for the
environment also change!
Evidence for Evolution
—  Darwin found evidence from a wide range of sources
to support his argument for natural selection.
Fossils
—  Older fossils are in lower
layers of rock than newer
fossils
—  Fossils were found of
many organisms that
had similar
characteristics, but were
different species than
living organisms
—  Types of fossils also
changed over time
Geography
—  Closely related species are usually found in areas
geographically close to each other
—  Species that live in similar conditions across the
world have similar adaptations
Embryology
—  There are structural similarities between the
embryos of many different species
Homologous Structures
—  Similar structure, different function-result of
common ancestor (Divergent evolution)
Analogous Structures
—  Different structure, same function-no common
ancestor (convergent evolution)
Vestigial Structures
—  Evolutionary leftovers-were useful in ancestors, but
no longer serve any purpose
DNA Sequence Analysis
—  The more closely related two organisms are, the
more DNA sequences they have in common
How Populations Evolve
Genetic Variation is a good thing!
—  More versions genes means that the population is
more resilient-if the environment changes, the
population is better equipped to survive it
Gene Pool
—  The number of different traits in a population
Sources of Variation
—  There is only one way for completely new traits to
enter into a population:
¡ 
Mutation
—  When new individuals enter a population through
migration, they also can bring new traits/variations
5 Mechanisms of Evolution
1.  Population shrinks (genetic drift)
2.  Sexual Selection
3.  Mutation
4.  Gene Flow
5.  Natural Selection
Microevolution vs. Macroevolution
—  Microevolution-changes in the gene pool
—  Macroevolution-new species
Types of Natural Selection
—  Directional
—  Stabilizing
—  Disruptive
Directional Selection
—  One extreme phenotype becomes more common
Stabilizing Selection
—  The intermediate phenotype becomes more
common, extremes are selected against
—  Intermediate trait is selected against, extreme
phenotypes become more common
Speciation
The process where reproductively isolated populations
evolve to become two different species.
Reproductive Isolation is Key to Speciation
—  Reproductive isolation is some kind of barrier that
prevents two members of different populations from
mating or producing offspring
What causes reproductive isolation?
—  Behavioral isolation-
differences in courtship
or mating behaviors
—  Geographic isolationphysical barriers that
divide a population into
two or more groups
—  Temporal isolationbarriers involving timing
of reproduction
Divergent Evolution
—  One common ancestor evolves into multiple species
Convergent
—  Unrelated species develop similar adaptations
Coevolution
—  Two species evolve in response to each other
Extinct vs. Extant
—  Extinct-no longer exists
—  Extant-still exists
Punctuated Equilibrium
—  Populations evolve very quickly, followed by periods
of stasis
Adaptive Radiation
—  Process where ancestral species diversifies rapidly
(hundreds to thousands of years) into many new
species after a change in the environment.