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 LamarckDarwin Inheritance soft hard

Differences between Lamarck’s and Darwin’s Theories LamarckDarwin Inheritance soft hard Extinction no yes

Differences between Lamarck’s and Darwin’s Theories LamarckDarwin Inheritance soft hard Extinction no yes Orthogenesis yes no

Differences between Lamarck’s and Darwin’s Theories LamarckDarwin Inheritance soft hard Extinction no yes Orthogenesis yes no Common descent no yes

Differences between Lamarck’s and Darwin’s Theories LamarckDarwin Inheritance soft hard Extinction no yes Orthogenesis yes no Common descent no yes Speciation no yes

Differences between Lamarck’s and Darwin’s Theories LamarckDarwin Inheritance soft hard Extinction no yes Orthogenesis yes no Common descent no yes Speciation no yes Role of environment “creates” “sorts” variationvariation

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 ( ) 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 Fittest Who survives?

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 Fittest Who survives?Who is the 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