Download Evolution and Natural Selection

History of Evolutionary Thought
• Species- a group of organisms that can
interbreed and produce fertile offspring.
• Before 1850, most people believed…
– The earth was formed by supernatural events
– Earth never changes.
– The earth was only a few thousand years old.
– Each species was made by a divine creator.
– Each species was made to fit its environment.
– Species never changed and did not go extinct.
Charles Darwin
• 02/12/1809 – 4/19/1882
• At age of 22, sailed on
•
“HMS Beagle” to
Galapagos islands
Believed God created each
species to match its
habitat and a species
never changed.
Charles Darwin cont.
• Five year journey, he
•
made observations
and recorded them in
a journal.
Darwin began to
doubt that species
remained “constant.”
James Hutton and Charles Lyell
• Founders modern geology.
• The crust of the earth has
•
•
been slowly changing over
time.
Some of earth’s
formations have taken
millions of years to form.
The earth is older than
what people thought.
George Cuvier
• Species can go extinct.
• Proved this studying
fossils.
• Ex.) Mammoth fossils
• The earths crust is
“layered” with fossils.
• Deeper crust = older
fossils
Jean Baptiste Lamarck
• Species change over time.
• Species can “acquire”
traits in their lifetime.
• Ex.) Big muscles.
• These traits can be passed
to offspring.
• Right idea, wrong
explanation.
Alfred Russell Wallace
• Studied different
species around the
world.
• There is a constant
struggle for food.
• Weaker individuals
will die out.
• Survival of the fittest.
Thomas Malthus
• Applied Wallace’s concept
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•
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•
to humans living in
London.
Population growth was
very high.
People were dying due to
starvation and disease.
The environment cannot
support everyone.
This applies to all species.
Lamark
Species do change
Wallace
Sent copy of his essay
to Darwin  Darwin
realized these were
same ideas he had
Malthus
Population ideas apply
to all species… Darwin
felt ideas applied even
more directly to plants
and animals
Lyell
Earth old enough for
change to occur,
causing Darwin to
question if life could
change as well?
Charles Darwin
• In 1859, Darwin published
“The Origin of Species.”
Major points of Darwin’s book:
• Organisms have traits that help them
survive.
• Species do change over time.
• These gradual changes may cause one
species to change into new species.
• African apes are close genetic
relatives of modern humans.
Darwin’s Theory –
Evolution by Natural Selection
What causes evolution?
• Evolution is the GENETIC change in members
•
•
•
•
•
•
of a species over time.
Darwin’s most important insight was that
members of a species vary.
Ex) Livestock
Farmers use variation in artificial selection or
“selective breeding”
Nature provides the variation, humans select
and breed useful variations to improve crops,
etc.
Later, Darwin stated reason for why species in
nature change…
Called “natural selection” …
Natural Selection
• Natural Selection is the “process” that
drives evolution.
• Process by which individuals that are
better suited to their environment
survive and reproduce most
successfully.
Natural Selection
1.) Every species contains variety. Causes?
2.) Living things face a constant struggle for
existence. Why?
3.) Only individuals that survive can reproduce.
“Survival of the fittest”?
Adaptation?
4.) Results in changes in the gene pool.
How is genetic change measured?
5.) Entire species is now better suited for
survival. HOW? If not?
Darwin’s Theory –
Evolution by Natural Selection
Natural Selection (Review)
• Variation (caused by genetics)= neck length
• More individuals than can survive= competition
for leaves in trees
• Members with best adaptation will survive and
•
reproduce – long neck
Results in genetic change= frequency long neck
allele increasing and short neck allele decreasing
• Results in next generation of the species being
“genetically better” than the previous generationnumber of giraffes with long neck more prevalent
in population
Evolution and Natural Selection
“Misconceptions”
• Q: Why is variation important?
• A: Variation is key because the environment an
organism lives in is constantly changing
-ex) England- factories/pollution
-What if amongst the moths there was no
variation… only peppered no dark…
-Result might have been… EXTINCTION
Evolution and Natural Selection
“Misconceptions”
• Q: What is an adaptation?
-adaptation is NOT a process by which organism
“changes” to survive
-It is incorrect to say… “When the environment
changed the dark moths were the best at adapting and
remained hidden from the birds.”
-It is also incorrect to say… “The moth population
adapted to the environment after the pollution increased
and thus lived.”
Evolution and Natural Selection
“Misconceptions”
• A: An adaptation is a trait an organism is born
with that because of what the environment is
like it increases the organism’s chances of
surviving
-peppered moths could not consciously change
their color from peppered to dark
-this is what you are implying if you write “the
dark moths were the best at adapting to …”
-NO organism can change its genetic traits
(DNA)
Evolution and Natural Selection
“Misconceptions”
• Q: Definition of evolution is- genetic change in a
species over time… What does genetic change
refer to?
-It is understood that an organism can NOT change its
DNA …so how does genetic change apply…
• A: Genetic change means changes in allele frequency in
the gene pool, which lead to changes in genotypic
frequency, and then changes in phenotypic frequency as
well
Evolution and Natural Selection
“Misconceptions”
• Q: Entire species is better suited … means…
• A: “The entire population of the species is now
better suited for survival.”
• Q: How would this apply to the peppered
•
moths?
A: The species of moths is now better suited for
survival because the population consists of mostly
dark moths.
Evolution and Natural Selection
• The definition of evolution is …
-genetic change amongst members of a species
-this is happening in the population in terms of
the alleles causing changes in both genotypic
and phenotypic frequencies…
Evolution and Natural Selection
• We can describe the genetic change amongst the
population two ways…
• Directional selection vs. balancing selection
• Both terms describe how the allele frequencies are
changing as a result of natural selection…
Evolution of Peppered Moths…
Genetic Change Amongst the Peppered Moth Population
1.2
1
Allele Frequencies
0.8
p
0.6
q
0.4
0.2
0
Year 1
Year 3
Year 5
Year
Year 7
Year 9
Evolution of Peppered Moths…
• Frequency of the dominant allele (p or
peppered) decreased
• Frequency of the recessive allele (q or
dark) increased
• This is directional selection
Directional Selection
• Frequency of an allele is
pushed in one direction
without opposition
Sickle Cell Anemia: The Puzzle
• Recessive disease
originated in Africa
• Africa
1/100 aa
• United States 1/500 aa
• Why has natural
selection not acted
against the sickle cell
allele (a) in Africa to
reduce its frequency?
Genetic Change Amongst the African
Population
Allele Frequeny
1.2
1
0.8
p
0.6
q
0.4
0.2
0
1
2
3
Year
4
5
Balancing Selection
• Two opposite forces affect the allele in a
population
• Allele frequency may vary year to year, but
over time usually remains same (value)
ex) sickle cell allele (aa) – lethal - death by sickle
cell = decrease
ex) sickle cell allele (a) – favorable - (Aa) resistant
to malaria = increase
ex) no sickle cell allele (AA) – lethal - death by
malaria = decrease
How Species Form?
• Natural selection favors variations
that increases a species survival.
• If environment changes, natural
selection will occur.
• Can members of a species change
enough to form a new species?
• Speciation- generation of a new
species
How Species Form?
• Ecological Races (subspecies)
– Populations of the same species that
differ genetically because they have
adapted to different living conditions.
– Still members of same species.
Why might members of
same species be separated?
• Different groups of subspecies may
•
•
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become isolated from each other.
Isolation makes it difficult for members
of the same species to mate.
Geographic Isolation
Populations separated into different
environments due to geographical
features (mountains, canyons, bodies of
water, etc.)
Speciation cont.
• When geographical isolation prevents
•
interbreeding for long periods of time,
populations in different places become
increasingly different due to different
environments.
Eventually if the groups can no longer
mate and create fertile offspring, they
will be considered separate species.
Macroevolution
• Evolutionary relationships on a “large scale”
• Scientists attempt to explain diversification of life
• Scientists attempt at determining how living
•
organisms on Earth are related to each other
“Common Ancestor”
• Ex) Charles Darwin said…
“Humans and apes shared a common ancestor”
“Modern day whales had a distant ancestor that
lived on land and walked on four limbs”
Evidence of Evolution
• Fossil Evidence
• Structural Evidence
• Developmental Evidence
• DNA Evidence
What is a fossil?
• Any traces of dead organisms.
• Organism must be buried by
sediment. Usually happens in
swamps, mud, tar pits, or the ocean
bottom.
• “Hard stuff” fossilizes.
What can fossils tell us?
• A glimpse into the history of an organisms
•
•
past.
Transitional species = “intermediate forms”
Ex.) Whale evolution
Structural Evidence
• Comparing the way two organisms are put
•
together to determine if related or share
common ancestor.
Homologous Structures: structures that are
similar in structure differ in function.
Analogous structures=
pertain to
the various structures in different species
having the same appearance structure or
function but have evolved separately thus
do not share common ancestor.
Structural Evidence cont.
• Vestigial structures: Structures reduced in
size and have no present function; “remants of
organism’s past”
Developmental Evidence
• Compares embryos of different species to determine
•
how closely organisms are related and whether or not
might share a common ancestor.
Longer early stages of development are similar between
organisms= more closely related
Fish Fish
Salamander
Tortoise
Chicken
Rabbit
Rabbit
Human
DNA Evidence
• DNA evidence supports the other three.
• If species change over time, their DNA will
also change.
• Similar organisms=similar DNA sequences
• More similar DNA = more closely related.