why is darwin’s theory of evolution by natural …...why is darwin’s theory of evolution by...
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Why is Darwin’s
Theory of Evolution
by Natural Selection
controversial?
Or is it?
Why is Darwin’s
Theory of Evolution
by Natural Selection
controversial?
Why is Darwin’s
Theory of Evolution
by Natural Selection
controversial?
Darwin: “species change and form from existing species by natural causes”
vs. species were created “as is” by supernatural causes
…and if new species form by natural causes, does that mean human moral and
rational faculties are the result of natural causes?
-> “humans descended from monkeys”
Why is Darwin’s
Theory of Evolution
by Natural Selection
controversial?
Darwin: “if new species can form, then given a lot of time, the many diverse forms of
life could descend from a common ancestor”
vs. the earth is about 8,000 years old
Darwinian evolution accepts (requires) the conclusion of geologists and physicists
that the earth is very old.
How old is the earth…
and life on earth?
How old is the earth…
and life on earth?
a. Simple eukaryotes b. prokaryotes
c. Cambrian explosion – major animal groups
e.
d.Place these events
on the timeline of
earth’s history
A brief overview of the earth’s history
4 3 2 1 todayTime - billions of years ago
Earth forms
Period of heavy
bombardment
Carbon isotope (first evidence of life)
First fossil microbes
Oldest eukaryotic fossil
dinosaurs
hominids
Animal diversity begins
Oxygen accumulates in atmosphere
Why is Darwin’s
Theory of Evolution
by Natural Selection
controversial?“Evolution is just a theory, and is has not been proven (nor can it be proven because
we can’t go back in time to observe it).”
A scientific theory is a well-substantiated explanation of some aspect of the natural world that is acquired
through the scientific method, and repeatedly confirmed through observation and experimentation. As with
most (if not all) forms of scientific knowledge, scientific theories are inductive and they aim for predictive
and explanatory force.
Cell theory, germ theory, big bang theory, theory of relativity, molecular orbital theory, transition state theory
some theories are discarded when evidence contradicts: Lamarkianism, Spontaneous generation of life, miasma theory of disease
A scientific law is a statement based on repeated experimental observations that describes
some aspect of the world. Laws differ from scientific theories in that they do not posit a
mechanism or explanation of phenomena: they are merely distillations of the results of
repeated observation.Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points.
Newton's law of universal gravitation states that any two bodies in the universe attract each other with a force that is directly proportional to the product
of their masses and inversely proportional to the square of the distance between them.
Hooke's law is a principle of physics that states that the force needed to extend or compress a spring by some distance is proportional to that distance.
The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but
cannot be created or destroyed.
Problem: How did the many diverse forms of life originate?Note: this is not the same as “how did life originate” (e.g. “molecules to man”)
Hypothesis:
1. New species come from previously existing species, and
2. divergent life-forms descended from a common ancestor.
Mechanism:
New species come from previous species by descent with
modification (evolution by natural selection)1. Organisms in a population are born with heritable variation of traits
2. The number of offspring outnumber resources, therefore there is a struggle to survive/reproduce
3. Individuals with some traits will survive/reproduce more than others
4. Over time, the population will change to have more individuals with the traits that promote
survival/reproduction, and hence the population will change to become adapted to its particular environment
Applying the scientific method
Problem: How did the many diverse forms of life originate?
Hypothesis:
1. New species form from previously existing species, and
2. divergent life-forms descended from a common ancestor
Mechanism:
New species form from previous species by descent with modification (evolution by
natural selection)
If so, then:
??
Applying the scientific method
Problem: How did the many diverse forms of life originate?
Hypothesis:
1. New species form from previously existing species, and
2. divergent life-forms descended from a common ancestor
Mechanism:
New species form from previous species by descent with modification (evolution by
natural selection)
If so, then:
1. We should be able to see transitional forms gradually accumulating modifications
of traits over time.
2. We might expect to directly observe species changing over time.
3. Species related by descent from a common ancestor should share traits they
inherited from that common ancestor.
4. Closely related species live near one another, while more distantly related species
are more geographically separated: Species living near each other should be more
similar (share more traits) because they are more closely related, while species
isolated from each other should have less traits in common because they are more
distantly related.
Applying the scientific method
Problem: How did the many diverse forms of life originate?
Alternate Hypothesis:
1. New species are created “as is” and do not change.
Mechanism:
Supernatural causes
If so, then:
??
Applying the scientific method
Problem: How did the many diverse forms of life originate?
Alternate Hypothesis:
1. New species are created “as is” and do not change.
Mechanism:
Supernatural causes
If so, then:
1. Fossils of all organismal types should be present at all geographic levels (ages)
2. And these fossils should not show signs of progression or change between levels.
3. Traits in organisms reflect the “acts of the creator”, without historical traces.
Note: Evolution addresses the origins of the diversity of life, not the origins of the first living organisms.
Scientist are still trying to understand how living organisms could originate from non-living chemicals
…but scientific explanations require reproducible observations (processes that follow natural laws) and not
super-natural causes.
Applying the scientific method
The Evidence for Evolution
What is found? Fossils exist and fossil forms are unlike species living today
1. Fossil Sequence?
When fossils are arranged according to their age, they show successive
evolutionary change
2. Fossil Intermediates?
Transitional fossils have been found between:
Amphibians & reptiles,
reptiles & birds,
reptiles & mammals,
apes and humans
1. We should be able to see transitional forms gradually accumulating modifications of traits over time.
2. We might expect to directly observe species changing over time.
3. Species related by descent from a common ancestor should share traits they inherited from that
common ancestor.
4. Closely related species live near one another, while more distantly related species are more
geographically separated: Species living near each other should be more similar (share more traits)
because they are more closely related, while species isolated from each other should have less traits in
common because they are more distantly related.
The Evidence for Evolution1. We should be able to see transitional forms gradually accumulating modifications of traits over time.
2. We might expect to directly observe species changing over time.
3. Species related by descent from a common ancestor should share traits they inherited from that
common ancestor.
4. Closely related species live near one another, while more distantly related species are more
geographically separated: Species living near each other should be more similar (share more traits)
because they are more closely related, while species isolated from each other should have less traits in
common because they are more distantly related.
The Evidence for Evolution1. We should be able to see transitional forms gradually accumulating modifications of traits over time.
2. We might expect to directly observe species changing over time.
3. Species related by descent from a common ancestor should share traits they inherited from that
common ancestor.
4. Closely related species live near one another, while more distantly related species are more
geographically separated: Species living near each other should be more similar (share more traits)
because they are more closely related, while species isolated from each other should have less traits in
common because they are more distantly related.
The fossil Record is Incomplete
Why is that?
The fossil Record is Incomplete
At the time of Darwin, the fossil record was VERY scanty. A great
deal of progress has been made since, but it is far from finished.
The fossil record is relatively incomplete for several reasons:
1. Soft tissues are rarely preserved
2. Movement of the earth's crust has obliterated and/or
covered many fossils
3. Fossilization takes place only in certain types of
habitats and favorable environments
4. Paleontologists have not dug up every place on earth
The Evidence for Evolution
Artificial Selection:
1. We should be able to see transitional forms gradually accumulating modifications of traits over time.
2. We might expect to directly observe species changing over time.
3. Species related by descent from a common ancestor should share traits they inherited from that
common ancestor.
4. Closely related species live near one another, while more distantly related species are more
geographically separated: Species living near each other should be more similar (share more traits)
because they are more closely related, while species isolated from each other should have less traits in
common because they are more distantly related.
The Evidence for Evolution
Artificial Selection:
1. We should be able to see transitional forms gradually accumulating modifications of traits over time.
2. We might expect to directly observe species changing over time.
3. Species related by descent from a common ancestor should share traits they inherited from that
common ancestor.
4. Closely related species live near one another, while more distantly related species are more
geographically separated: Species living near each other should be more similar (share more traits)
because they are more closely related, while species isolated from each other should have less traits in
common because they are more distantly related.
The Evidence for Evolution1. We should be able to see transitional forms gradually accumulating modifications of traits over time.
2. We might expect to directly observe species changing over time.
3. Species related by descent from a common ancestor should share traits they inherited from that
common ancestor.
4. Closely related species live near one another, while more distantly related species are more
geographically separated: Species living near each other should be more similar (share more traits)
because they are more closely related, while species isolated from each other should have less traits in
common because they are more distantly related.
Natural Selection:
antibiotic resistance in
bacteria
“beak length” in
soapberry bug
The Evidence for Evolution
The underlying design of each structure is similar despite their functional differences
Homologous structures: bones of the forelimb
1. We should be able to see transitional forms gradually accumulating modifications of traits over time.
2. We might expect to directly observe species changing over time.
3. Species related by descent from a common ancestor should share traits they inherited from that
common ancestor.
4. Closely related species live near one another, while more distantly related species are more
geographically separated: Species living near each other should be more similar (share more traits)
because they are more closely related, while species isolated from each other should have less traits in
common because they are more distantly related.
The Evidence for Evolution
Homologous structures in adults develop from homologous groups of cells in embryos
(they share developmental pathways)
Homologous structures in embryos indicate common ancestry
1. We should be able to see transitional forms gradually accumulating modifications of traits over time.
2. We might expect to directly observe species changing over time.
3. Species related by descent from a common ancestor should share traits they inherited from that
common ancestor.
4. Closely related species live near one another, while more distantly related species are more
geographically separated: Species living near each other should be more similar (share more traits)
because they are more closely related, while species isolated from each other should have less traits in
common because they are more distantly related.
The Evidence for Evolution
• Features that have no apparent function
• Typically have an important function in
related species
• reflect history of change
• Ex: Hindlimb joints in whales.
• What other animal has vestigial
hindlimbs?
Vestigial structures – an interesting kind of homologous structure
1. We should be able to see transitional forms gradually accumulating modifications of traits over time.
2. We might expect to directly observe species changing over time.
3. Species related by descent from a common ancestor should share traits they inherited from that
common ancestor.
4. Closely related species live near one another, while more distantly related species are more
geographically separated: Species living near each other should be more similar (share more traits)
because they are more closely related, while species isolated from each other should have less traits in
common because they are more distantly related.
Vestigial Structures in Humans
Appendix
Wisdom Teeth
Tailbone
Vestigial Structures in blind cave fish
The Evidence for Evolution1. We should be able to see transitional forms gradually accumulating modifications of traits over time
2. We might expect to directly observe species changing over time
3. Species related by descent from a common ancestor should share traits they inherited from that
common ancestor.
4. Closely related species live near one another, while more distantly related species are more
geographically separated: Species living near each other should be more similar (share more traits)
because they are more closely related, while species isolated from each other should have less traits in
common because they are more distantly related.
Homologous molecular structures in all life:
Central dogma (DNA -> mRNA -> protein)
Universal codon table
Protein sequences are similar:
hemoglobin
DNA polymerase
cytochrome oxidase, and thousands more
The Evidence for Evolution1. We should be able to see transitional forms gradually accumulating modifications of traits over time.
2. We might expect to directly observe species changing over time.
3. Species related by descent from a common ancestor should share traits they inherited from that
common ancestor.
4. Closely related species live near one another, while more distantly related species are more
geographically separated: Species living near each other should be more similar (share more traits)
because they are more closely related, while species isolated from each other should have less traits in
common because they are more distantly related.
Species that are extremely similar to one another
tend to be clustered geographically, for example:
Darwin’s finches
Hawaiian honeycreepers
The law of succession: Living species are more
similar to fossil species in the same geographic
area than they are to living species in other areas.
Geographic Distributions
Wolves are native to North America, North Africa, and Eurasia
Hares and rabbits are native to North America, Africa, and Eurasia
Cactuses are native to North America
Geographic Distributions
Tasmanian “wolf” Patagonian hare African spurge
Wolves are native to North America, North Africa, and Eurasia
Hares and rabbits are native to North America, Africa, and Eurasia
Cactuses are native to North America
Convergent Evolution
Homology vs. Analogy
Natural selection appears to have favored similar adaptations
independently in distantly related organisms living in similar
environments --> these are analogous structures
homologous structures:
have similar structure (because of
common ancestry),
but do not necessarily have similar
function (because the organisms adapted
differently by divergent evolution).
analogous structures:
have similar function (because of similar
selective pressures),
but the structures are only superficially
similar (because each adaptation evolved
independently by convergent evolution)