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Evolution
Change in life on Earth
Evolution
• Phylogeny : the evolutionary history
of a group of organisms.
• Often drawn as a tree
Charles Darwin
• English naturalist
• Traveled the world
for 5 years on the
HMS Beagle
• Darwin first
produced evidence
of evolution of
living things from a
common ancestor
Charles Darwin
• Darwin identified
natural selection as
the process for
evolution.
• Natural selection :
mechanism for
change in
populations.
Natural Selection
• Natural selection
proceeds in steps
• 1. In nature,
organisms produce
more offspring
than can survive.
(overproduction)
Natural Selection
• 2. Individuals have
variations.
• This may be color,
size, or speed
Natural Selection
• 3. Individuals with
certain useful
characteristics
(variation) survive
in a struggle for
existence.
Natural Selection
• 4. Over time, the
more successful
variations are
“selected” and the
species will
gradually change.
Natural Selection
• This gradual
change in
characteristics
changes the
population’s gene
pool.
• Gene pool : all
available genes for
a population
Evidence of Evolution
• Fossils provide a
record of early
life.
• Fossils of a species
can show change
over time.
Evidence of Evolution
• Homologous
structures:
structures with the
same evolutionary
origin.
• Can be the same in
arrangement,
function or both.
Evidence of Evolution
• Embryology : the
study of the
developing embryo.
• The shared
features of the
young embryos
suggest evolution
from a common
ancestor.
Evidence of Evolution
• Vestigial
structures : a
structure in a
present day
organism that no
longer serves its
original purpose.
• Probably useful to
its ancestor
Evidence of Evolution
• Biochemical :
nearly all organisms
share DNA, ATP
and many enzymes.
• The code for amino
acids is the same in
organisms.
• The more similar
the DNA between
2 organisms, the
more closely
related
Results of Natural Selection
• Speciation : new
species is formed
when similar
populations no
longer interbreed.
• Species: group of
organisms that can
breed and
reproduce
• Some obstacle may
separate
populations.
Results of Natural Selection
Results of Natural Selection
• Diversity : a large
variety of
organisms.
• The more diversity
the healthier the
ecosystem.
Results of Natural Selection
• Genetic Drift : Change in gene
frequency. (how often you see a trait)
• Especially in small populations.
• Recessive trait is expressed
• Results in a decrease in diversity.
Polydactyl
Results of Natural Selection
• Divergent
evolution: related
species become
less alike.
Results of Natural Selection
• Convergent
evolution: unrelated
species become
more alike.
Results of Natural Selection
• Extinction : species
may vanish
• Can be a mass
extinction like
dinosaurs.
Paths of Evolution
• Gradualism :
gradual change
over time in a
species
Which fossils are the oldest?
Paths of Evolution
• Punctuated
equilibrium :
relatively quick
evolution followed
by long periods of
equilibrium.
• Big change in
environment, or
new predator