Unit 7: Theory of Evolution

Unit 7: Theory of Evolution
The history…
• A long time ago
people had no idea just
how old the Earth
truly is (4.6 billion
years old).
• They wondered about
the fossils they found
of animals that no
longer existed. Where
had they all gone?
Charles Darwin
• was a young man, whom
in 1831 was the naturalist
(zoologist, botanist) on
board a an English ship,
the H.M.S. Beagle.
• During their five year
mission who studied
things that helped him
develop the his theory of
The Galápagos
• He visited the Galápagos
Islands and studied its
plants and animals.
• These were unique to
their islands but similar to
species elsewhere.
• Darwin noticed that
species seemed perfectly
built to survive on the
particular islands on
which they all lived.
The Finches
• Each island was home
to its own species of
• Each finch had a beak
that seemed just right
for whatever food was
• What do you think that
these different species
each ate?
The Tortoises
• The Galápagos were
named for the shells of
the giant tortoises found
there that resembled
saddles (Galápagos).
• The tortoise above has a
peaked shell and long
neck, allowing to reach
the high vegetation that
grows on its island.
• The tortoise below has a
low domed shell and
feeds on grasses found
on its island.
So for the next two decades…
• Darwin continued
refining his ideas
about evolution.
• He noticed that when
he breed pigeons
with desirable traits
they produced
offspring with those
same traits.
• Breeding organisms
to produce specific
traits is called
artificial selection.
Darwin explain natural selection
• Natural selection is a
mechanism for change
in populations. it
occurs when
organisms with
favorable variations
survive, reproduced
and pass their
variations to the next
Step by step…
• Fact 1:
• organisms
produce more
offspring than
can survive.
They compete
for food, water,
space, mates,
Fact 2
• Variation exists
individuals in
any species.
Some may be
larger, faster,
less heavy, more
colorful, etc.
Fact 3
• Individuals
exists with
useful variations
for their
• They survive,
reproduce and
pass those
variation or
on to their
Fact 4
• Over time, individuals
with these favorable
characteristics will
make up most of the
population and may
look totally different
from their ancestors.
An example
• A long time ago, in a
savanna far, far away…
a species of deer existed
that needed to eat. But
there was not enough
food to go around.
Some individuals were a
little taller and could
reach the lower branches
on trees to eat. So they
did not need to eat just
And so..
• More of the tall ones
lived and had babies.
• And their babies
looked like them.
• Every generation some
babies were born that
were shorter and some
that were taller. The
taller ones survived
longer and so had
more chances to
reproduce. Their
babies were usually
And over time we got….
of the tall ones
There are several forms of
evidence for evolutionary theory.
structural adaptations
1. Fossils
• provide a record of
early life and
evolutionary history.
• The further down a
fossil is found the
older it is.
• The record is
• Fossils have lead us to
believe that whales
evolved from landdwelling, doglike
2. Anatomy
a. homologous structures
b. analogous structures
c. vestigial structures
2a. Homologous Structures
• are structural features with a common
evolutionary origin.
• The bones in the human arm are also found in
cats, whales and bats.
2b. Analogous Structures
• are body parts of organisms that do not have a common
evolutionary origin but are similar in function.
• The wings of birds, bats and insects all evolved
independently to similar ways of life.
2c. Vestigial Structures
• are body
structures in a
organism that no
longer serves its
original purpose,
but was probably
useful to an
3. Embryology
• embryos are the
earliest stage of
growth of
development of both
plants and animals.
• The embryos of fish,
reptiles birds and
humans look
surprisingly similar .
4. Biochemistry
• Nearly all organisms share DNA, ATP and many
enzymes among their chemical molecules.
5. Structural Adaptations
• Mimicry is a
structural adaptation
that allows one
species to resemble
another species.
• Camouflage is an
adaptation that
enables species to
blend with their
Physiological adaptations can develop fast.
• Some antibiotics that were used 50 years ago are now
useless against certain disease causing bacteria.
The 3 Types of Natural Selection
1. stabilizing selection
2. directional selection
3. disruptive selection
• Natural selection is
survival of the fittest.
• This means those
individuals that are
better suited to a given
environment; not
necessarily the biggest
or strongest
Stabilizing Selection
• is natural selection that
favors average
individuals in a
Directional Selection
• occurs when natural selection favors one of the extremes of
a trait.
• This can be the smallest, longest, strongest or darkest.
Disruptive Selection
• is when individuals with either extreme of a trait’s variation
are selected for
The Evolution of Species
• The evolution of a new species is called
Geographic Isolation
• occurs whenever a physical barrier divides a population.
Reproductive Isolation
• occurs when
organisms can
longer mate and
produce fertile
• refers to an organism
with a multiple if the
normal set of
• This can result in
death or defect but can
also result in new
species, especially in
Speciation rates
• Gradualism is the idea
that species originate
through a gradual
change of adaptations.
• Punctuated
equilibrium is the
hypothesis that argues
that speciation occurs
relatively quickly, in
rapid bursts, with long
periods of genetic
equilibrium in
Patterns of Evolution
• Divergent Evolution (adaptive radiation) is the
patter of evolution in which species that once were
similar to an ancestral species diverge, or become
Patterns of Evolution
• Convergent evolution
is one in which
distantly related
organisms evolve
similar traits.

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