Transcript Theory of Evolution By Natural Selection

Evolution By Natural Selection
1
Isn’t Evolution Just A Theory?
Video clip: learning and teaching evolution NP-VT 576.8 min 0-7
• How does the scientific meaning of a term
like theory differ from the way it is used in
everyday life?
• Can the “facts” of science change over
time? If so, how?
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Evolution
• Scientific theories
– Concepts based on the conclusions of
observations and experiments.
– A well tested explanation that unifies a broad
range of observations.
– Supported by a large number of observations
and not yet found lacking.
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Evolution
Cell
All organisms are composed of cells.
Biogenesis
Life comes only from life.
Gene
Organisms contain coded information
that dictates their form, function, and
behavior.
All living things have a common
ancestor. Genetic changes in a
population or species over
generations have led to the diversity
of life on Earth.
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Evolution
Introduction
• Evolution: change over time by which modern organisms
have descended from ancient organisms.
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How Does Evolution Really Work?
Video clip: learning and teaching evolution NP-VT 576.8 min 20-27
• What are the 4 components of natural
selection?
• What determines an individual hummingbird’s
beak length?
• What factors in the environment might select
for beak length and shape within the
hummingbird population?
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Introduction
• Natural selection:
– Individuals that are better suited
to their environment are more
likely to survive and reproduce
than those that do not have such
traits.
– testable scientific explanation of
the process by which life on
earth has changed over time.
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Modern understanding of Natural selection
• In nature populations
produce more offspring than
environment can support
 struggle for existence
 survival of the “fittest”
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Modern understanding of Natural selection
1) Populations of a species
have genetic variation
-random mutation creates
new alleles for the
gene pool
-Sexual reproduction
shuffles genetics to
create unique
individuals
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Evolution by Natural selection overview
2)
Certain
phenotypes are
better suited to an
environment
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Modern understanding of Natural selection
3)
Over time, the genetic traits that
make certain individuals better at
surviving & reproducing have
more offspring
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Modern understanding of Natural selection
4) Natural selection selects for phenotypes (physical
characteristics) - ex. Lizard color coded for by genes.
• Alters the gene frequency (microevolution)
Predict what it will the gene frequency be at Gen 40
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Natural selection and Heterozygous individuals
• Lethal recessive alleles – how can they hide in a gene pool?
– Dominant allele: functioning chloride ion channel  healthy lungs
– Recessive cystic fibrosis allele: nonfunctioning ion channel  airways
clogged with mucus and early death
• Sickle cell Heterozygous advantage
– Natural protection against malaria parasite
– No complications of being homozygous
For sickle cell
X
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How Do We Know Evolution Happens
Video clip: learning and teaching evolution NP-VT 576.8 min 14-20
• How do fossils give us a picture of change
over time?
• What distinguishing feature of the fossil
Pakicetus skull identified it as related to a
whale? Why was this surprising?
• Why do scientists seek fossils that are
intermediate in form and time between
modern forms and their probable earliest
ancestors?
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Review of Current Evidence of Evolution
Vestigial
Tail bone
Vestigial
thigh bones
human
monkey
rabbit
chicken
turtle
*
 Has mammary glands
frog
 warm blooded
tuna
Lamprey
Has foramen
Magnum forward*
 Has opposable thumb
 Has amnion (can have offspring away from water)
 Has a paired legs
 Has paired appendages & spinal coard
*the opening between
 Has a Dorsal nerve cord
which the brain and the
spinal cord make
connections
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Review of Current Evidence of Evolution
Fossils from
50 mya
Change over many generations
*
Modern
Baleen whale
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Genetic Drift
• Genetic drift may occur when a small group of individuals colonizes a
new habitat.
• Individuals may carry alleles in different relative frequencies than did
the larger population from which they came.
• The new population will be genetically different from the parent
population.
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Species and Speciation
Species: a group of organisms
that breed with one another
and produce fertile offspring
Speciation: the formation of
new species
Isolating Mechanisms: As a
new species evolves,
populations become isolated
from one another
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Isolation
• Temporal Isolation
prezygotic
– can live in same
place but breeds at
different times
– Frog example 
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Isolation
Behavioral isolation:
courtship rituals
prezygotic
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Isolation
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Isolation
• Geographic isolation:
– population split by barrier (ex: river, mountain…)
Evidence Common ancestor
Separated 10,000 years ago
different sides of the Grand Canyon
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Macroevolution: back to the big picture
• Macroevolution refers to large-scale evolutionary patterns
and processes that occur over long periods of time.
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Macroevolution: back to the big picture
Auxiliary video 4 Billion Year war – 1hr movie: McKay
Extinction
• More than 99% of all species that have ever lived are now
extinct.
• In the past, most researchers looked for a single, major
cause for each mass extinction.
• Many paleontologists now think that mass extinctions were
caused by several factors.
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Macroevolution: back to the big picture
• What effects have mass extinctions
had on the history of life? Mass
extinctions have:
– provided ecological opportunities for
organisms that survived
– resulted in bursts of evolution that
produced many new species
• Punctuated equilibrium is a pattern
of evolution in which long stable
periods are interrupted by brief
periods of more rapid change.
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