chapter 3 darwinian natural selection. the mechanism of natural selection in the last chapter we...
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Chapter 3Chapter 3Darwinian Natural SelectionDarwinian Natural Selection
The Mechanism of Natural SelectionThe Mechanism of Natural Selection
In the last chapter we discussed the evidence that evolution occurs
Now we examine HOW it occurs Darwin tied together pattern with
process Why his argument was so elegant...
In the last chapter we discussed the evidence that evolution occurs
Now we examine HOW it occurs Darwin tied together pattern with
process Why his argument was so elegant...
Darwin’s Four PostulatesDarwin’s Four Postulates
1. Individual species are variable
2. Some variation is passed on to offspring
3. More young are born than can survive
4. Survival and reproduction are not random Individuals with most favorable variations
survive to reproduce more Natural selection, or survival of the fittest
1. Individual species are variable
2. Some variation is passed on to offspring
3. More young are born than can survive
4. Survival and reproduction are not random Individuals with most favorable variations
survive to reproduce more Natural selection, or survival of the fittest
Darwin’s Four PostulatesDarwin’s Four Postulates
HIV There is variation among virions in their
resistance to AZT The ability to distinguish between AZT and
thymidine is inherited Not all virions are able to infect T cells and
reproduce The virions that distinguish AZT the best
produce more offspring and are naturally selected for
HIV There is variation among virions in their
resistance to AZT The ability to distinguish between AZT and
thymidine is inherited Not all virions are able to infect T cells and
reproduce The virions that distinguish AZT the best
produce more offspring and are naturally selected for
Fitness and AdaptationFitness and Adaptation
Individuals who win the competition and survive to reproduce are more fit
Darwinian fitness is the ability of an individual to survive and reproduce in its environment
An adaptation is a trait that increases an individual’s fitness in its environment
Adaptations are enhanced and favored by natural selection
Individuals who win the competition and survive to reproduce are more fit
Darwinian fitness is the ability of an individual to survive and reproduce in its environment
An adaptation is a trait that increases an individual’s fitness in its environment
Adaptations are enhanced and favored by natural selection
Darwin’s Four PostulatesDarwin’s Four Postulates
Alfred Russel Wallace had independently developed the theory of natural selection before Darwin published his book
Wallace is not as famous because Darwin’s argument was more complete and he eventually published it first
The four postulates can be independently verified Natural selection is testable
Alfred Russel Wallace had independently developed the theory of natural selection before Darwin published his book
Wallace is not as famous because Darwin’s argument was more complete and he eventually published it first
The four postulates can be independently verified Natural selection is testable
Finch Beak Evolution in the Galápagos IslandsFinch Beak Evolution in the Galápagos Islands
Peter and Rosemary Grant Studying Darwin’s finches since 1973 14 finch species Species differ in overall size, beak
dimensions, and other characters Variation in beak morphology tied to
feeding habits Insects, seeds, nectar, parasites, leaves, fruit
Peter and Rosemary Grant Studying Darwin’s finches since 1973 14 finch species Species differ in overall size, beak
dimensions, and other characters Variation in beak morphology tied to
feeding habits Insects, seeds, nectar, parasites, leaves, fruit
Finch Beak Evolution in the Galápagos IslandsFinch Beak Evolution in the Galápagos Islands
Study of ground finches on Daphne Major Very small island Distant from others Good natural laboratory Finches cannot easily disperse to or from
Daphne Major
Study of ground finches on Daphne Major Very small island Distant from others Good natural laboratory Finches cannot easily disperse to or from
Daphne Major
Finch Beak Evolution in the Galápagos IslandsFinch Beak Evolution in the Galápagos Islands
Geospiza fortis, medium ground finch 1200 finch individuals on island
All marked Eats seeds
Crack by grasping at base of bill and applying force Beak size is variable within species
Bigger beaks eat bigger seed species Smaller beaks eat smaller seed species
Geospiza fortis, medium ground finch 1200 finch individuals on island
All marked Eats seeds
Crack by grasping at base of bill and applying force Beak size is variable within species
Bigger beaks eat bigger seed species Smaller beaks eat smaller seed species
Evolutionof GalapagosFinches
Evolutionof GalapagosFinches
Finch Beak Evolution in the Galápagos IslandsFinch Beak Evolution in the Galápagos Islands
Testing Postulate 1: Are Populations Variable? Because each finch is marked, each can be
measured Weight, wing length, beak width, beak depth,
beak length, etc. Beak depth is variable within this species
Testing Postulate 1: Are Populations Variable? Because each finch is marked, each can be
measured Weight, wing length, beak width, beak depth,
beak length, etc. Beak depth is variable within this species
Beak depth in medium ground finches on Daphne Major in 1976.
VARIATION
Beak depth in medium ground finches on Daphne Major in 1976.
VARIATION
Finch Beak Evolution in the Galápagos IslandsFinch Beak Evolution in the Galápagos Islands
Testing Postulate 2: Is Variation Heritable? Beak depth variation could be genetic or
environmental Must estimate heritability
Proportion of variation observed in a population due to variation in the effects of genes
Compare parents and offspring Beak depth is heritable
Testing Postulate 2: Is Variation Heritable? Beak depth variation could be genetic or
environmental Must estimate heritability
Proportion of variation observed in a population due to variation in the effects of genes
Compare parents and offspring Beak depth is heritable
Heritability of beak depth in G. fortis. VARIATION IS HERITABLE
Heritability of beak depth in G. fortis. VARIATION IS HERITABLE
Finch Beak Evolution in the Galápagos IslandsFinch Beak Evolution in the Galápagos Islands
Testing Postulate 3: Is There an Excess of Offspring so that Only Some Individuals Live to Reproduce? In 1977 there was a severe drought
84% of finch population died
In normal times 89% of finches die before they reproduce
Clearly, more individuals are born than can survive and reproduce
Testing Postulate 3: Is There an Excess of Offspring so that Only Some Individuals Live to Reproduce? In 1977 there was a severe drought
84% of finch population died
In normal times 89% of finches die before they reproduce
Clearly, more individuals are born than can survive and reproduce
Ex. of Exponential Growth and Its Potential Role in Selection…Ex. of Exponential Growth and Its Potential Role in Selection…
Wallace: 1 pair birds produces 4 young per year each pair produce 4 times in a life 15 years each pair produces 10 million birds
Darwin: Elephant lives 100 yrs, produces about 6 progeny between 30-90 1 pr produces 19 million in 750 yrs if all offsp.
reproduce
Wallace: 1 pair birds produces 4 young per year each pair produce 4 times in a life 15 years each pair produces 10 million birds
Darwin: Elephant lives 100 yrs, produces about 6 progeny between 30-90 1 pr produces 19 million in 750 yrs if all offsp.
reproduce
Brodie: 2 Bullfrogs-----50,000 eggs/life (frog = .5 lb; egg mass=25 cm2)
if 10 survive (.02%)...........250,000 eggs
if .02% surv. (50 frogs).......1,250,100 eggs
250 frogs.......6,250,000 eggs (4th generation)
by 10th gen. 19,531,250......~500 billion eggs
which is about 2 sq km of eggs and about 10,000 (9,866 tons) of frog
Brodie: 2 Bullfrogs-----50,000 eggs/life (frog = .5 lb; egg mass=25 cm2)
if 10 survive (.02%)...........250,000 eggs
if .02% surv. (50 frogs).......1,250,100 eggs
250 frogs.......6,250,000 eggs (4th generation)
by 10th gen. 19,531,250......~500 billion eggs
which is about 2 sq km of eggs and about 10,000 (9,866 tons) of frog
Finch Beak Evolution in the Galápagos IslandsFinch Beak Evolution in the Galápagos Islands
Testing Postulate 4: Are Survival and Reproduction Nonrandom? After drought, the Grants measured the surviving
birds again Found that finches with deepest beaks survived
more than others Deep beaks were favorable during drought
because only one plant produced a lot of fruit Tribulus cistoides has large, hard fruits Only birds with deep, narrow beaks can crack them
Testing Postulate 4: Are Survival and Reproduction Nonrandom? After drought, the Grants measured the surviving
birds again Found that finches with deepest beaks survived
more than others Deep beaks were favorable during drought
because only one plant produced a lot of fruit Tribulus cistoides has large, hard fruits Only birds with deep, narrow beaks can crack them
Result of 1977 DroughtResult of 1977 Drought
Seed abundance droppedSeed abundance dropped
Bird abundance droppedBird abundance dropped
Average type of seeds available for food on Daphne Major
Average type of seeds available for food on Daphne Major
Finch Beak Evolution in the Galápagos IslandsFinch Beak Evolution in the Galápagos Islands
Testing Postulate 4: Are Survival and Reproduction Nonrandom? Natural selection caused deep beaks to be
favored during the drought Other birds died out Other droughts produced similar effects El Niño produced the opposite
A very wet year caused the production of small, soft seeds Small birds with shallow beaks were selected for
Natural Selection is dynamic
Testing Postulate 4: Are Survival and Reproduction Nonrandom? Natural selection caused deep beaks to be
favored during the drought Other birds died out Other droughts produced similar effects El Niño produced the opposite
A very wet year caused the production of small, soft seeds Small birds with shallow beaks were selected for
Natural Selection is dynamic
Natural selection caused deep beaks to be favored during the drought
Natural selection caused deep beaks to be favored during the drought
Natural selection caused deep beaks to be favored during the drought
LOOK HOW PRONOUNCED TREND IS IN NEXT YEAR’S OFFSPRING!
Natural selection caused deep beaks to be favored during the drought
LOOK HOW PRONOUNCED TREND IS IN NEXT YEAR’S OFFSPRING!
Finch Beak Evolution in the Galápagos IslandsFinch Beak Evolution in the Galápagos Islands
Did evolution occur? Natural selection acted on finch
population Evolution is a response to selection A change in populations over generations To know if evolution occurred, must see if
characteristics changed over time ....Evolution did occur
Did evolution occur? Natural selection acted on finch
population Evolution is a response to selection A change in populations over generations To know if evolution occurred, must see if
characteristics changed over time ....Evolution did occur
30 Years of evolution in Daphne Major finches30 Years of evolution in Daphne Major finches
The Nature of Natural SelectionThe Nature of Natural Selection
Even though the process is quite simple, it is sometimes difficult to think statistically to understand natural selection
Will discuss popular ideas about natural selection that are incorrect
Show how natural selection does and does not operate
Even though the process is quite simple, it is sometimes difficult to think statistically to understand natural selection
Will discuss popular ideas about natural selection that are incorrect
Show how natural selection does and does not operate
The Nature of Natural SelectionThe Nature of Natural Selection
Natural selection acts on individuals but evolution occurs in populations When HIV virions are exposed to AZT or finches
are exposed to changes in seed availability, those selected individuals are not changed
They just live through selection event and produce more offspring than others
The populations of finches or virions then change, not the individuals
Natural selection acts on individuals but evolution occurs in populations When HIV virions are exposed to AZT or finches
are exposed to changes in seed availability, those selected individuals are not changed
They just live through selection event and produce more offspring than others
The populations of finches or virions then change, not the individuals
The Nature of Natural SelectionThe Nature of Natural Selection
Natural selection acts on phenotypes, but evolution changes allele frequencies If deep beaks had not been heritable, the deep
beaked individuals would have survived the drought, but evolution could not have occurred because the trait would not be passed on to the offspring
The next generation would still have a wide range of beak depths
Natural selection can only act on traits that have a genetic basis
Natural selection acts on phenotypes, but evolution changes allele frequencies If deep beaks had not been heritable, the deep
beaked individuals would have survived the drought, but evolution could not have occurred because the trait would not be passed on to the offspring
The next generation would still have a wide range of beak depths
Natural selection can only act on traits that have a genetic basis
The Nature of Natural SelectionThe Nature of Natural Selection
Natural selection is backward looking, not forward looking Each generation is a product of selection by the
environmental conditions from the generation before
AZT resistant virions and deep beaked finches are well adapted to the situations introduced in their parent’s generation
If there is a new environmental change, they may not be well adapted to it
Organisms cannot adapt to future conditions, only those in the past
Natural selection is backward looking, not forward looking Each generation is a product of selection by the
environmental conditions from the generation before
AZT resistant virions and deep beaked finches are well adapted to the situations introduced in their parent’s generation
If there is a new environmental change, they may not be well adapted to it
Organisms cannot adapt to future conditions, only those in the past
The Nature of Natural SelectionThe Nature of Natural Selection
Natural selection can produce new traits, even though it acts on existing traits Can select from variation present
Cannot instantly create a new beak for cracking a certain fruit
Over time, natural selection can produce new traits
New mutations every generation for natural selection to act upon
Natural selection can produce new traits, even though it acts on existing traits Can select from variation present
Cannot instantly create a new beak for cracking a certain fruit
Over time, natural selection can produce new traits
New mutations every generation for natural selection to act upon
The Nature of Natural SelectionThe Nature of Natural Selection
Artificial selection experiment Started with 163 ears of corn Found variation of 4–6% oil content Selected 24 ears with highest oil content per
generation for 60 years Now those ears have 16% oil No overlap with original population Evolution produced a new trait
Artificial selection experiment Started with 163 ears of corn Found variation of 4–6% oil content Selected 24 ears with highest oil content per
generation for 60 years Now those ears have 16% oil No overlap with original population Evolution produced a new trait
The Nature of Natural SelectionThe Nature of Natural Selection
Natural selection can also lead to novel traits Selection can repurpose traits for new
functions Giant panda’s thumb
Used to strip bamboo stalks “thumb” is actually a wrist bone modified to act as a
thumb Must have been variation in size of wrist bone and
selection for elongation Preadaptation, or exaptation
Natural selection can also lead to novel traits Selection can repurpose traits for new
functions Giant panda’s thumb
Used to strip bamboo stalks “thumb” is actually a wrist bone modified to act as a
thumb Must have been variation in size of wrist bone and
selection for elongation Preadaptation, or exaptation
Giant Panda’s ThumbGiant Panda’s Thumb
The Nature of Natural SelectionThe Nature of Natural Selection
Natural selection is not perfect Can only work with variation present Finches with deep, narrow beaks can break hard
seeds the best Most of the selected birds had wide beaks
Genes for wide beaks and deeps beaks must be linked
Natural selection could not make the perfect beak because the genes for it were not present
Adaptation, not perfection
Natural selection is not perfect Can only work with variation present Finches with deep, narrow beaks can break hard
seeds the best Most of the selected birds had wide beaks
Genes for wide beaks and deeps beaks must be linked
Natural selection could not make the perfect beak because the genes for it were not present
Adaptation, not perfection
The Nature of Natural SelectionThe Nature of Natural Selection
Natural selection is nonrandom, but not progressive Natural selection increases adaptation
but is not directional We see trend to increased complexity but
some organisms decrease in complexity Tapeworm Snake Cave fish
Natural selection is nonrandom, but not progressive Natural selection increases adaptation
but is not directional We see trend to increased complexity but
some organisms decrease in complexity Tapeworm Snake Cave fish
The Nature of Natural SelectionThe Nature of Natural Selection
Natural selection acts on individuals, not groups Organisms are never self-sacrificing or
altruistic Only endanger themselves for selfish gain
Prairie dog alarm calls Lions nursing other cubs
Do so because of relatedness or reciprocity
Natural selection acts on individuals, not groups Organisms are never self-sacrificing or
altruistic Only endanger themselves for selfish gain
Prairie dog alarm calls Lions nursing other cubs
Do so because of relatedness or reciprocity
The Evolution of DarwinismThe Evolution of Darwinism
Since Darwin did not know about mutation, he had no idea how variation was generated in populations
Since Darwin did not know about genetics, he did not understand how variations were passed to offspring The Idea of blending inheritance
Since Darwin did not know about mutation, he had no idea how variation was generated in populations
Since Darwin did not know about genetics, he did not understand how variations were passed to offspring The Idea of blending inheritance
The (Wrong) Idea of Blending InheritanceThe (Wrong) Idea of Blending Inheritance
Genes are like pigments in paint... Mixing two colors of paint (i.e., the mixing
of genes from parents) would result in an even blend of traits (in offspring)...
We know this is not the case... although some phenotypes of offspring may be
intermediate between those of parents GENOTYPES ARE DISTINCT, DISCRETE
CHARACTERS! E.g. Mammalian Hair Color...
Genes are like pigments in paint... Mixing two colors of paint (i.e., the mixing
of genes from parents) would result in an even blend of traits (in offspring)...
We know this is not the case... although some phenotypes of offspring may be
intermediate between those of parents GENOTYPES ARE DISTINCT, DISCRETE
CHARACTERS! E.g. Mammalian Hair Color...
Evolution of DarwinismEvolution of Darwinism
Evolution is the unifying theory of biology
Was not the standard in biology until 70 years after Darwin’s publication
Darwin’s ideas had three problems that had to be solved before full acceptance on evolution by natural selection
Evolution is the unifying theory of biology
Was not the standard in biology until 70 years after Darwin’s publication
Darwin’s ideas had three problems that had to be solved before full acceptance on evolution by natural selection
History of Evolutionary Thought History of Evolutionary Thought
I. Early Ideas of Change the Greeks
II. Darwinian Revolution Intellectual environment pre-Darwin Change as
a concept Darwin and contemporaries III. Post Darwin
Blending Inheritance Mendel Biometrics IV. The Modern Synthesis
Hardy-Weinberg Dobzhansky Haldane, Fisher, Wright Recent innovations
I. Early Ideas of Change the Greeks
II. Darwinian Revolution Intellectual environment pre-Darwin Change as
a concept Darwin and contemporaries III. Post Darwin
Blending Inheritance Mendel Biometrics IV. The Modern Synthesis
Hardy-Weinberg Dobzhansky Haldane, Fisher, Wright Recent innovations
Natural Selection (by Darwin and Wallace)Natural Selection (by Darwin and Wallace)
Did not incorporate any element of inheritance, taken for granted
that parents produce like offspring
Did not incorporate any element of inheritance, taken for granted
that parents produce like offspring
Evolution of DarwinismEvolution of Darwinism
Darwin did not know how variability was created Thought that variation in organisms would
be used up eventually New variation created continuously by
mutation
Darwin did not know how variability was created Thought that variation in organisms would
be used up eventually New variation created continuously by
mutation
Evolution of DarwinismEvolution of Darwinism
Darwin did not know how traits were inherited Believed in blending inheritance
Individual traits would be lost by merging with other traits
After Mendel was re-discovered we know that alleles are inherited independently
Darwin did not know how traits were inherited Believed in blending inheritance
Individual traits would be lost by merging with other traits
After Mendel was re-discovered we know that alleles are inherited independently
Mendelian inheritanceMendelian inheritance
Gregor Mendel (Czech Monk) performed experiments demonstrating particulate inheritance in mid 1800's but they were unknown until "rediscovered" by De Vries and Tschermak
Initially a great blow, because characters that are controlled by one or a few loci exhibit discrete variation -- differences between genotypes was too big to fit into Darwin's theory
Gregor Mendel (Czech Monk) performed experiments demonstrating particulate inheritance in mid 1800's but they were unknown until "rediscovered" by De Vries and Tschermak
Initially a great blow, because characters that are controlled by one or a few loci exhibit discrete variation -- differences between genotypes was too big to fit into Darwin's theory
The Modern SynthesisThe Modern Synthesis
For first 70 years after Origin of Species was published, biology was in turmoil
Between 1932 and 1953 the Modern Synthesis answered Darwin’s original problems with new data
For first 70 years after Origin of Species was published, biology was in turmoil
Between 1932 and 1953 the Modern Synthesis answered Darwin’s original problems with new data
Biometricians Biometricians
Karl Pearson, August Weismann, Francis Galton were demonstrating that most genes have only small effect, and that most variation is continuous
(eg, body size, speed, vs eye color) this fit fine into Darwinian theory
Karl Pearson, August Weismann, Francis Galton were demonstrating that most genes have only small effect, and that most variation is continuous
(eg, body size, speed, vs eye color) this fit fine into Darwinian theory
The Modern SynthesisThe Modern Synthesis
Again around the 1930's, Natural Selection and gradual evolution started to come back, primarily through the efforts of a few geneticists responsible for what is now called the New Synthesis or Neo-Darwinian theory.
Primarily combines genetics, mathematics and evolutionary theory into a set of ideas called population genetics
Again around the 1930's, Natural Selection and gradual evolution started to come back, primarily through the efforts of a few geneticists responsible for what is now called the New Synthesis or Neo-Darwinian theory.
Primarily combines genetics, mathematics and evolutionary theory into a set of ideas called population genetics
The Modern SynthesisThe Modern Synthesis
Grounded in two propositions Gradual evolution results from small
genetic changes that are acted upon by natural selection
The origin of species and higher taxa, macroevolution, can be explained in terms of natural selection acting on individuals, microevolution
Grounded in two propositions Gradual evolution results from small
genetic changes that are acted upon by natural selection
The origin of species and higher taxa, macroevolution, can be explained in terms of natural selection acting on individuals, microevolution
Hardy-Weinberg (-Castle) theorem Hardy-Weinberg (-Castle) theorem
A demonstration that frequencies of genes do not change from one generation to the next if all members mate at random and there is no advantage to any gene. This is the foundation of all population genetics, because by adding terms for selection and migration, it can be shown that gene frequencies do change in the face of very weak forces.
A demonstration that frequencies of genes do not change from one generation to the next if all members mate at random and there is no advantage to any gene. This is the foundation of all population genetics, because by adding terms for selection and migration, it can be shown that gene frequencies do change in the face of very weak forces.
The MODERN SYNTHESIS The MODERN SYNTHESIS
Theodosius Dobzhansky (1900-1975)Theodosius Dobzhansky (1900-1975)
With fruitflies, revealed hidden genetic variation and demonstrated that the differences between races and species were genetic --- led to the understanding that species are not "morpho-types" but variable populations that are reproductively isolated from one another
One of the main fathers of the New Synthesis, by combining genetics with the more established views of evolutionary process
With fruitflies, revealed hidden genetic variation and demonstrated that the differences between races and species were genetic --- led to the understanding that species are not "morpho-types" but variable populations that are reproductively isolated from one another
One of the main fathers of the New Synthesis, by combining genetics with the more established views of evolutionary process
The MODERN SYNTHESIS The MODERN SYNTHESIS
Other Major PlayersOther Major Players
Sewall Wright: used Guinea pig as eraser, worked on polydactyly and coat color in guinea pigs. He was an intimidating mathematician, pioneer in multivariate approaches to evolution. Developed shifting balance theory of maintenance of variation
R. A. Fisher: Competing mathematician and father of linear statistics (Regression); "The Genetical Theory of Natural Selection"
Sewall Wright: used Guinea pig as eraser, worked on polydactyly and coat color in guinea pigs. He was an intimidating mathematician, pioneer in multivariate approaches to evolution. Developed shifting balance theory of maintenance of variation
R. A. Fisher: Competing mathematician and father of linear statistics (Regression); "The Genetical Theory of Natural Selection"
The MODERN SYNTHESIS The MODERN SYNTHESIS
Recent Innovations Recent Innovations
Cladistics -- Willi Hennig, a new and more rigorous means of approaching questions of relationship founded on a specific model of evolution including parsimony
Neutral Theory -- Mootoo Kimura, suggested that most evolution is neutral and has no effect on the phenotype, based on the idea that most changes to DNA do not have noticeable effects on phenotype
Cladistics -- Willi Hennig, a new and more rigorous means of approaching questions of relationship founded on a specific model of evolution including parsimony
Neutral Theory -- Mootoo Kimura, suggested that most evolution is neutral and has no effect on the phenotype, based on the idea that most changes to DNA do not have noticeable effects on phenotype
Recent Challenges or InnovationsRecent Challenges or Innovations
Punctuated equilibrium -- Stephen Jay Gould & Niles Eldridge, later Stephen Stanley; motivated by observation that fossil record tends to reflect a less continuous change than expected by gradual change. Referred to by some as “evolution by jerks”. Non-constant mode and rate of evolution, at times suggested that most evolutionary change occurs at level of species-selection
Punctuated equilibrium -- Stephen Jay Gould & Niles Eldridge, later Stephen Stanley; motivated by observation that fossil record tends to reflect a less continuous change than expected by gradual change. Referred to by some as “evolution by jerks”. Non-constant mode and rate of evolution, at times suggested that most evolutionary change occurs at level of species-selection
The Modern SynthesisThe Modern Synthesis
Can re-state Darwin’s postulates As a result of mutation creating new
alleles, and segregation and independent assortment shuffling alleles into new combinations, individuals within populations are variable for nearly all traits
Individuals pass their alleles on to their offspring
Can re-state Darwin’s postulates As a result of mutation creating new
alleles, and segregation and independent assortment shuffling alleles into new combinations, individuals within populations are variable for nearly all traits
Individuals pass their alleles on to their offspring
The Modern SynthesisThe Modern Synthesis
Can re-state Darwin’s postulates In most generations, more offspring are
produced than can survive
Individuals that survive and reproduce, or who reproduce the most, are those with alleles and allelic combinations that best adapt them to their environment
Can re-state Darwin’s postulates In most generations, more offspring are
produced than can survive
Individuals that survive and reproduce, or who reproduce the most, are those with alleles and allelic combinations that best adapt them to their environment
The Modern SynthesisThe Modern Synthesis
We also now know, as Darwin suspected, that natural selection is not the only cause of evolution
It is usually the primary cause
Will examine other mechanisms for evolution later in the course
We also now know, as Darwin suspected, that natural selection is not the only cause of evolution
It is usually the primary cause
Will examine other mechanisms for evolution later in the course
Scientific Creationism DebateScientific Creationism Debate
Evolution totally accepted by biologists since Modern Synthesis
Political and philosophical controversy still exists in U.S.
Scopes Monkey Trial of 1925 John Scopes taught evolution to his
students despite a Tennessee law preventing the teaching of Darwinism
Evolution totally accepted by biologists since Modern Synthesis
Political and philosophical controversy still exists in U.S.
Scopes Monkey Trial of 1925 John Scopes taught evolution to his
students despite a Tennessee law preventing the teaching of Darwinism
Scientific Creationism DebateScientific Creationism Debate
Scopes Monkey Trial of 1925 A widely publicized trial William Jennings Bryan prosecutor Clarence Darrow defense attorney The prosecution won but Scopes was only
fined $100 and the prosecution looked ridiculous in their arguments
Considered a win for Darwinism
Scopes Monkey Trial of 1925 A widely publicized trial William Jennings Bryan prosecutor Clarence Darrow defense attorney The prosecution won but Scopes was only
fined $100 and the prosecution looked ridiculous in their arguments
Considered a win for Darwinism
Scientific Creationism DebateScientific Creationism Debate
In 1967 U.S. Supreme Court struck down state laws prohibiting teaching of evolution
Fundamentalists reformed argument to be called Creation Science Wanted equal time in schools
In 1987 Supreme Court declared a religious idea could not be taught in public schools Violates first amendment
In 1967 U.S. Supreme Court struck down state laws prohibiting teaching of evolution
Fundamentalists reformed argument to be called Creation Science Wanted equal time in schools
In 1987 Supreme Court declared a religious idea could not be taught in public schools Violates first amendment
Scientific Creationism DebateScientific Creationism Debate
Recently, a new name (with similar ideas) has been used for the creationist viewpoint: Intelligent Design Theory Discuss “organs of extreme perfection” The vertebrate eye example... William Paley in 1802 stated that if you found
a watch you would assume that it had to be made by an intelligent creator
He said it is the same for the vertebrate eye It is too intricate and complex to arise from
random events
Recently, a new name (with similar ideas) has been used for the creationist viewpoint: Intelligent Design Theory Discuss “organs of extreme perfection” The vertebrate eye example... William Paley in 1802 stated that if you found
a watch you would assume that it had to be made by an intelligent creator
He said it is the same for the vertebrate eye It is too intricate and complex to arise from
random events
Scientific Creationism DebateScientific Creationism Debate
Of course, natural selection is not random
According to Darwin, the vertebrate eye must have arisen from simpler eyes that evolved in grades
Found examples of intermediate eyes from other living organisms that probably mimic the evolutionary pathway of the vertebrate eye
Of course, natural selection is not random
According to Darwin, the vertebrate eye must have arisen from simpler eyes that evolved in grades
Found examples of intermediate eyes from other living organisms that probably mimic the evolutionary pathway of the vertebrate eye
Variation in mollusc eyesVariation in mollusc eyes
Simple pigmented spot
Simple pigmented cup
Optic cup in Abalone
Complex lensed eyes of marine snail Littorina
Complex lensed eyes of an octopus
Simple pigmented spot
Simple pigmented cup
Optic cup in Abalone
Complex lensed eyes of marine snail Littorina
Complex lensed eyes of an octopus
Another arguement that has been used to discount evolution..:
Irreducibility complex – single system in which all of its multiple parts are required for function
Eukaryotic flagella example
Is it reasonable to think that multiple complex parts can be derived evolutionarily through the mechanisms we know operate in nature??
Co-option of Crystalline genes example...
Another arguement that has been used to discount evolution..:
Irreducibility complex – single system in which all of its multiple parts are required for function
Eukaryotic flagella example
Is it reasonable to think that multiple complex parts can be derived evolutionarily through the mechanisms we know operate in nature??
Co-option of Crystalline genes example...
Scientific Creationism DebateScientific Creationism Debate
Gene co-option crystallins of animal eye lensesGene co-option crystallins of animal eye lenses
Scientific Creationism DebateScientific Creationism Debate
“Because organisms progress from simpler to more complex forms evolution violates the second law of thermodynamics” Organisms do not necessarily evolve to
be more complex The second law, entropy, only applies to
closed systems The earth is an open system with plants
capturing light from the sun
“Because organisms progress from simpler to more complex forms evolution violates the second law of thermodynamics” Organisms do not necessarily evolve to
be more complex The second law, entropy, only applies to
closed systems The earth is an open system with plants
capturing light from the sun
SummarySummary
For our purposes, we need to remember that if we are discussing science, evidence must be allowed to make scientific decisions
The evidence for evolution is compelling and, single handedly, explains essentially all facets of patterns in biology
It is important to recognize the simplistic requirements for evolution, upon which we will continue to build details and examples for the next several months...
For our purposes, we need to remember that if we are discussing science, evidence must be allowed to make scientific decisions
The evidence for evolution is compelling and, single handedly, explains essentially all facets of patterns in biology
It is important to recognize the simplistic requirements for evolution, upon which we will continue to build details and examples for the next several months...
Darwin’s Four PostulatesDarwin’s Four Postulates
1. Individual species are variable
2. Some variation is passed on to offspring
3. More young are born than can survive
4. Survival and reproduction are not random Individuals with most favorable variations
survive to reproduce more Natural selection, or survival of the fittest
1. Individual species are variable
2. Some variation is passed on to offspring
3. More young are born than can survive
4. Survival and reproduction are not random Individuals with most favorable variations
survive to reproduce more Natural selection, or survival of the fittest
The Modern SynthesisThe Modern Synthesis
Restating Darwin’s postulates As a result of mutation creating new
alleles, and segregation and independent assortment shuffling alleles into new combinations, individuals within populations are variable for nearly all traits
Individuals pass their alleles on to their offspring
Restating Darwin’s postulates As a result of mutation creating new
alleles, and segregation and independent assortment shuffling alleles into new combinations, individuals within populations are variable for nearly all traits
Individuals pass their alleles on to their offspring
The Modern SynthesisThe Modern Synthesis
Restating Darwin’s postulates In most generations, more offspring are
produced than can survive
Individuals that survive and reproduce, or who reproduce the most, are those with alleles and allelic combinations that best adapt them to their environment
Restating Darwin’s postulates In most generations, more offspring are
produced than can survive
Individuals that survive and reproduce, or who reproduce the most, are those with alleles and allelic combinations that best adapt them to their environment