Download (Part 2) The formulation of Theory of natural selection

BIOE 109 Evolution
Summer 2009
Lecture 2- Part II
Formulation of theory of natural selection
Darwin’s “Five Theories”
Darwin’s “Five Theories”
1. Evolution per se
Darwin’s “Five Theories”
1. Evolution per se
• the world is steadily changing and populations of
organisms are transformed over time.
Darwin’s “Five Theories”
1. Evolution per se
• the world is steadily changing and populations of
organisms are transformed over time.
2. Common descent
Darwin’s “Five Theories”
1. Evolution per se
• the world is steadily changing and populations of
organisms are transformed over time.
2. Common descent
• every group of organisms has descended from a
common ancestor.
Darwin’s “Five Theories”
1. Evolution per se
• the world is steadily changing and populations of
organisms are transformed over time.
2. Common descent
• every group of organisms has descended from a
common ancestor.
• all species can ultimately be traced to a single origin
of life on earth.
• this “dethroned” man from the pinnacle of “scala naturae”
Darwin’s tree of life
Tree of Life: the first-known sketch by Charles Darwin of an evolutionary tree
describing the relationships among groups of organisms.
“Life had been originally breathed into a few
forms or into one” (Origin, page 490)
Caricatures of Darwin…
London Sketch Book, 1874
Hornet Magazine, 1872
Darwin’s “Five Theories”
3. Multiplication of species
Darwin’s “Five Theories”
3. Multiplication of species
• this process is now called “speciation”.
Darwin’s “Five Theories”
3. Multiplication of species
• this process is now called “speciation”.
• Darwin’s view similar to what is now called allopatric
speciation.
Darwin’s “Five Theories”
3. Multiplication of species
• this process is now called “speciation”.
• Darwin’s view similar to what is now called allopatric
speciation.
4. Gradualism
Darwin’s “Five Theories”
3. Multiplication of species
• this process is now called “speciation”.
• Darwin’s view similar to what is now called allopatric
speciation.
4. Gradualism
• most evolutionary change occurs slowly.
Darwin’s “Five Theories”
3. Multiplication of species
• this process is now called “speciation”.
• Darwin’s view similar to what is now called allopatric
speciation.
4. Gradualism
• most evolutionary change occurs slowly.
5. Natural selection
Darwin’s “Five Theories”
3. Multiplication of species
• this process is now called “speciation”.
• Darwin’s view similar to what is now called allopatric
speciation.
4. Gradualism
• most evolutionary change occurs slowly.
5. Natural selection
• this was Darwin’s mechanism for how evolutionary
change occurred.
• very few supported this explanation.
Similarities between Lamarck’s and
Darwin’s theories
Similarities between Lamarck’s and
Darwin’s theories
1. Lineages change over time - “evolution” occurs.
Similarities between Lamarck’s and
Darwin’s theories
1. Lineages change over time - “evolution” occurs.
2. A continually changing world drives evolutionary
change.
Similarities between Lamarck’s and
Darwin’s theories
1. Lineages change over time - “evolution” occurs.
2. A continually changing world drives evolutionary
change.
3. The rate of change is slow (gradualism).
Differences between Lamarck’s and
Darwin’s Theories
Differences between Lamarck’s and
Darwin’s Theories
Lamarck
Inheritance
soft
Darwin
hard
Differences between Lamarck’s and
Darwin’s Theories
Lamarck
Darwin
Inheritance
soft
hard
Extinction
no
yes
Differences between Lamarck’s and
Darwin’s Theories
Lamarck
Darwin
Inheritance
soft
hard
Extinction
no
yes
Orthogenesis
yes
no
Differences between Lamarck’s and
Darwin’s Theories
Lamarck
Darwin
Inheritance
soft
hard
Extinction
no
yes
Orthogenesis
yes
no
Common descent
no
yes
Differences between Lamarck’s and
Darwin’s Theories
Lamarck
Darwin
Inheritance
soft
hard
Extinction
no
yes
Orthogenesis
yes
no
Common descent
no
yes
Speciation
no
yes
Differences between Lamarck’s and
Darwin’s Theories
Lamarck
Darwin
Inheritance
soft
hard
Extinction
no
yes
Orthogenesis
yes
no
Common descent
no
yes
Speciation
no
yes
Role of environment
“creates”
variation
“sorts”
variation
The Darwinian Revolution
The Darwinian Revolution
Darwin’s theory challenged the most basic
beliefs of his day:
The Darwinian Revolution
Darwin’s theory challenged the most basic
beliefs of his day:
1. The belief in a constant world of limited age.
The Darwinian Revolution
Darwin’s theory challenged the most basic
beliefs of his day:
1. The belief in a constant world of limited age.
2. The belief in a world designed by a wise and benign
creator.
The Darwinian Revolution
Darwin’s theory challenged the most basic
beliefs of his day:
1. The belief in a constant world of limited age.
2. The belief in a world designed by a wise and benign
creator.
3. The belief in the immutability of species.
The Darwinian Revolution
Darwin’s theory challenged the most basic
beliefs of his day:
1. The belief in a constant world of limited age.
2. The belief in a world designed by a wise and benign
creator.
3. The belief in the immutability of species.
4. The belief in the unique position of man in creation.
The Darwinian Revolution
Darwin’s theory challenged the most basic
beliefs of his day:
1. The belief in a constant world of limited age.
2. The belief in a world designed by a wise and benign
creator.
3. The belief in the immutability of species.
4. The belief in the unique position of man in creation.
5. The belief in the philosophy of essentialism.
Darwin’s formulation of the principle of
natural selection
Darwin’s formulation of the principle of
natural selection
Example of a syllogism
Darwin’s formulation of the principle of
natural selection
Example of a syllogism – “a form of reasoning
in which a conclusion is drawn from two or
more given, or assumed, propositions”.
Darwin’s formulation of the principle of
natural selection
Fact 1: Natural populations have large excess
reproductive capacities.
Darwin’s formulation of the principle of
natural selection
Fact 1: Natural populations have large excess
reproductive capacities.
Fact 2: Population sizes generally remain stable.
Darwin’s formulation of the principle of
natural selection
Fact 1: Natural populations have large excess
reproductive capacities.
Fact 2: Population sizes generally remain stable.
Fact 3: Resources are limiting.
Darwin’s formulation of the principle of
natural selection
Fact 1: Natural populations have large excess
reproductive capacities.
Fact 2: Population sizes generally remain stable.
Fact 3: Resources are limiting.
Inference 1: A severe struggle for existence must
occur in nature.
Robert Thomas Malthus (1766-1834)
An essay on the principle of population, 1798
Darwin’s formulation of the principle
of natural selection
Fact 4: An abundance of variation exists
among individuals of a species.
Darwin’s formulation of the principle
of natural selection
Fact 4: An abundance of variation exists
among individuals of a species.
Fact 5: A proportion of this variation is
heritable.
Darwin’s formulation of the principle
of natural selection
Fact 4: An abundance of variation exists
among individuals of a species.
Fact 5: A proportion of this variation is
heritable.
Inference 2: Genetically superior individuals
will outsurvive and/or outreproduce others.
Darwin’s formulation of the principle
of natural selection
Fact 4: An abundance of variation exists
among individuals of a species.
Fact 5: A proportion of this variation is
heritable.
Inference 2: Genetically superior individuals
will outsurvive and/or outreproduce others.
Inference 3: Over many generations,
evolutionary change occurs in the population.
Evolution by natural selection can be defined as:
“changes in the relative frequencies
of different genotypes (genes) in a population
because of differences in the survivorship and/or
reproduction of their phenotypes”.
Objections to evolution by natural selection:
1. Objections from essentialists- selection can never
touch the underlying “essence” of species
2. Objections from creationists
Objections to evolution by natural selection:
1. Objections from essentialists- selection can never
touch the underlying “essence” of species
2. Objections from creationists
3. Ambiguity of the term “selection”- it implies
someone who selects (is “nature” a replacement of God?)
Objections to evolution by natural selection:
1. Objections from essentialists- selection can never
touch the underlying “essence” of species
2. Objections from creationists
3. Ambiguity of the term “selection”- it implies
someone who selects (is “nature” a replacement of God?)
Survive
Who survives?
Fittest
Objections to evolution by natural selection:
1. Objections from essentialists- selection can never
touch the underlying “essence” of species
2. Objections from creationists
3. Ambiguity of the term “selection”- it implies
someone who selects (is “nature” a replacement of God?)
Survive
Who survives?
Who is the fittest?
Fittest
Objections to evolution by natural selection:
1. Objections from essentialists- selection can never
touch the underlying “essence” of species
2. Objections from creationists
3. Ambiguity of the term “selection”- it implies
someone who selects (is “nature” a replacement of God?)
4. Probabilistic nature of evolution
Objections to evolution by natural selection:
1. Objections from essentialists- selection can never
touch the underlying “essence” of species
2. Objections from creationists
3. Ambiguity of the term “selection”- it implies
someone who selects (is “nature” a replacement of God?)
4. Probabilistic nature of evolution
Step 1: genetic variation is created
Objections to evolution by natural selection:
1. Objections from essentialists- selection can never
touch the underlying “essence” of species
2. Objections from creationists
3. Ambiguity of the term “selection”- it implies
someone who selects (is “nature” a replacement of God?)
4. Probabilistic nature of evolution
Step 1: genetic variation is created
Step 2: variation is sorted due to process of selection
Objections to evolution by natural selection:
1. Objections from essentialists- selection can never
touch the underlying “essence” of species
2. Objections from creationists
3. Ambiguity of the term “selection”- it implies
someone who selects (is “nature” a replacement of God?)
4. Probabilistic nature of evolution
5. Objections to methods used- inductive vs.
hypothetico-deductive
Objections to evolution by natural selection:
1. Objections from essentialists- selection can never
touch the underlying “essence” of species
2. Objections from creationists
3. Ambiguity of the term “selection”- it implies
someone who selects (is “nature” a replacement of God?)
4. Probabilistic nature of evolution
5. Objections to methods used- inductive vs.
hypothetico-deductive
6. Absence of proof