Transcript Unit 7: Theory of Evolution

Unit G: 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 an English ship, the
H.M.S. Beagle.
• During their five year
mission he studied things
that helped him develop
his theory of evolution.
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
finch.
• Each finch had a beak
that seemed just right
for whatever food was
available.
• 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 bred pigeons with
desirable traits they
produced offspring
with those same
traits.
• Breeding organisms
to produce specific
traits is called
artificial selection.
Darwin explained natural
selection
• Natural selection is a
mechanism for change
in populations. It
occurs when
organisms with
favorable variations
survive, reproduce and
pass their variations to
the next generation.
Step by step…
• Fact 1:
Competition
• organisms
produce more
offspring than
can survive.
They compete
for food, water,
space, mates,
etc.
Fact 2
• Variation exists
among
individuals in
any species.
Some may be
larger, faster,
less heavy,
more colorful,
etc.
Fact 3
• Individuals exist
with useful
variations for
their
environment.
• They survive,
reproduce and
pass those
variation or
characteristics
on to their
offspring.
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
grass.
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
taller. More of the tall
ones survived.
And over time we got….
• THE GIRAFFE!
There are several forms of
evidence for evolutionary theory.
•
•
•
•
•
fossils
anatomy
embryology
biochemistry
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
incomplete.
• Fossils have lead us to
believe that whales
evolved from landdwelling, doglike
creatures.
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
present-day
organism that no
longer serves its
original purpose,
but was probably
useful to an
ancestor.
3. Embryology
• embryos are the
earliest stage of
growth and
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
surroundings.
Physiological adaptations can develop fast.
• Some antibiotics that were used 50 years ago are now
useless against certain disease causing bacteria.
IMPORTANT
• 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
individuals.
The 3 Types of Natural Selection
1. stabilizing selection
2. directional selection
3. disruptive selection
Stabilizing Selection
• is natural selection that
favors average
individuals in a
population.
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
speciation.
Geographic Isolation
• occurs whenever a physical barrier divides a population.
Reproductive Isolation
• occurs when
formerly
interbreeding
organisms can no
longer mate and
produce fertile
offspring.
Polyploid
• refers to an organism
with a multiple of the
normal set of
chromosomes.
• This can result in
death or defect but can
also result in new
species, especially in
plants.
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
between.
Patterns of Evolution
• Divergent Evolution (adaptive radiation) is the
pattern of evolution in which species that once
were similar to an ancestral species diverge, or
become different.
Patterns of Evolution
• Convergent evolution
is one in which
distantly related
organisms evolve
similar traits.
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