Lecture 2 The Darwinian Revolution Theories of evolution
• first developed by the Greek philosophers.
Theories of evolution
• first developed by the Greek philosophers.
• Anaximander (610-546 BC) wrote about the sudden appearance of humans from fish- like creatures.
Is this evolution?
Is this evolution?
NO! It is “spontaneous generation”!
Two characteristics of spontaneous generation were common to early Greek philosophers:
Two characteristics of spontaneous generation were common to early Greek philosophers:
1. Resulted from the generative powers of nature (i.e., not actions of a God).
Two characteristics of spontaneous generation were common to early Greek philosophers:
1. Resulted from the generative powers of nature (i.e., not actions of a God).
2. Were nonteleological (i.e., without an underlying design or goal).
The influence of Aristotle (384-322 BC)
Plato and Aristotle The influence of Aristotle (384-322 BC)
1. All species are fixed and eternal
The influence of Aristotle (384-322 BC)
1. All species are fixed and eternal
• evolution not possible!
The influence of Aristotle (384-322 BC)
2. The philosophy of essentialism
The influence of Aristotle (384-322 BC)
2. The philosophy of essentialism
• each species represented by its “eidos”
The influence of Aristotle (384-322 BC)
2. The philosophy of essentialism
• each species represented by its “eidos”
• variation among individuals of a species is not “real”, nor important.
The influence of Aristotle (384-322 BC)
3. The scala naturae or “great chain of being”
The influence of Aristotle (384-322 BC)
3. The scala naturae or “great chain of being”
• refers to a linear progression of organisms from most simple to most complex.
The influence of Aristotle (384-322 BC)
3. The scala naturae or “great chain of being”
• refers to a linear progression of organisms from most simple to most complex.
• over time, believed to reflect the actions of a creator.
A 1579 drawing of the scala naturae How did evolutionary thinking develop?
How did evolutionary thinking develop?
1. The scientific revolution
How did evolutionary thinking develop?
1. The scientific revolution
• Astronomy → earth not the center of the universe!
How did evolutionary thinking develop?
1. The scientific revolution
• Astronomy → earth not the center of the universe!
• Geology → evidence for great age of earth, study of fossils
How did evolutionary thinking develop?
1. The scientific revolution
• Astronomy → earth not the center of the universe!
• Geology → evidence for great age of earth, study of fossils
2. The discovery of new faunas
How did evolutionary thinking develop?
1. The scientific revolution
• Astronomy → earth not the center of the universe!
• Geology → evidence for great age of earth, study of fossils
2. The discovery of new faunas
3. Extinction
How did evolutionary thinking develop?
4. The microscope
How did evolutionary thinking develop?
4. The microscope
• provided support for “spontaneous generation”.
How did evolutionary thinking develop?
4. The microscope
• provided support for “spontaneous generation”.
5. Development of the science of systematics
How did evolutionary thinking develop?
4. The microscope
• provided support for “spontaneous generation”.
5. Development of the science of systematics
• undermined the scala naturae.
Evolution according to Lamarck (1744-1829)
Evolution according to Lamarck (1744-1829)
Recognized two causes of evolutionary change:
Evolution according to Lamarck (1744-1829)
Recognized two causes of evolutionary change:
1. Life has an innate potential to acquire greater and greater complexity.
Evolution according to Lamarck (1744-1829)
Recognized two causes of evolutionary change:
1. Life has an innate potential to acquire greater and greater complexity.
- now called “orthogenesis”.
Recognized two causes of evolutionary change:
2. Organisms “reacted” to their environments and changed form.
Recognized two causes of evolutionary change:
2. Organisms “reacted” to their environments and changed form.
• changes were then transmitted to subsequent generations.
Recognized two causes of evolutionary change:
2. Organisms “reacted” to their environments and changed form.
• changes were then transmitted to subsequent generations.
• now called the “inheritance of acquired characteristics” or “soft inheritance”. The science of epigenetics Lamarck’s theory of organic progression
Charles Darwin Alfred Russel Wallace Thomas Robert Malthus (1766-1834)
Evolution according to Charles Darwin (1809-1882) Evolution according to Charles Darwin (1809-1882)
- publication of “On the origin of species by means of natural selection or the preservation of favored races in the struggle for life” (“The origin”) occurred in 1859. Darwin had two main objectives in writing this book
Darwin’s objectives:
1. To make the case that evolution had occurred.
Darwin’s objectives:
1. To make the case that evolution had occurred.
2. To provide a mechanism for how evolutionary change occurs.
Alfred Russel Wallace and the Ternate paper Alfred Russel Wallace and the Ternate paper 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.
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.
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. 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 Darwin
Inheritance soft 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” “sorts”
variation variation
The Darwinian Revolution
The Darwinian Revolution
Darwin’s theory challenged the prevailing beliefs of his day:
The Darwinian Revolution
Darwin’s theory challenged the prevailing beliefs of his day:
1. The belief in a constant world of limited age.
The Darwinian Revolution
Darwin’s theory challenged the prevailing 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 prevailing 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 prevailing 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 prevailing 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.
Evolution in action: the HIV virus
Peter and Rosemary Grant
Barry Sinervo The HIV/AIDS pandemic Life expectancy in Botswana What is HIV?
What is HIV?
• HIV is a retrovirus (i.e., RNA-based) with 9 genes
What is HIV?
• HIV is a retrovirus (i.e., RNA-based) with 9 genes
• is diploid (i.e., has 2 copies of each RNA strand)
The life cycle of HIV Q: How does HIV cause AIDS?
Q: How does HIV cause AIDS?
A: By attacking a key player in our immune system – CD4 helper T cells.
The role of helper T cells in the immune response The progression of an HIV infection Changes in CD4 T-cell count during HIV infection The life cycle of HIV Natural selection, AZT, and the
HIV virus
• What is AZT?
Natural selection, AZT, and the
HIV virus
• What is AZT?
• AZT (azidothymidine) is a base analogue.
Structure of azidothymidine Natural selection, AZT, and the
HIV virus
• What is AZT?
• AZT (azidothymidine) is a base analogue.
• Incorporation of AZT (instead of T) by reverse transcriptase halts replication.
How AZT blocks reverse transcriptase Evolution of AZT resistance Resistance evolves in the polymerase’s active site Evolution of the HIV virus Resistance to AZT has evolved in all patients taking the drug (usually in ~6 months)!
• This is an example of parallel evolution.
How does HIV evolve so rapidly?
How does HIV evolve so rapidly?
1. High mutation rate
• HIV’s mutation rate is 106 higher than ours!
How does HIV evolve so rapidly?
1. High mutation rate
• HIV’s mutation rate is 106 higher than ours!
2. Short generation time
• 1 year ≅ 300 viral generations.
How does HIV evolve so rapidly?
1. High mutation rate
• HIV’s mutation rate is 106 higher than ours!
2. Short generation time
• 1 year ≅ 300 viral generations.
10 years of viral ≅ 2-3 x 106 years of evolution human evolution!
Evolution of HIV within an individual patient Where did HIV come from?
Phylogeny of HIV-1 and related viruses Where did HIV come from?
• HIV “jumped” to humans multiple times from different primate hosts.
Where did HIV come from?
• HIV “jumped” to humans multiple times from different primate hosts.
Where did HIV come from?
• HIV “jumped” to humans multiple times from different primate hosts.
• Inter-species transfers of infectious diseases are called zoonoses.
Other examples of zoonoses…
Malaria (P. falciparum) Marburg fever Cholera Leishmaniasis Plague Hantavirus Dengue fever Toxoplasmosis H1N1 swine flu Rabies Ebola Ringworms SARS Cowpox West Nile virus Lyme disease Creutzfeldt-Jakob disease Yellow fever
Human Plasmodium falciparum
Chimpanzee Plasmodium spp.
see Rich et al. Proc. Natl. Acad. Sci. U.S.A. 106: 14902
Dating the origin of HIV-1 in humans Dating the origin of HIV-1 in humans Dating the origin of HIV-1 in humans Q: Why is HIV infection usually fatal?
Q: How do viruses achieve reproductive success?
Q: How do viruses achieve reproductive success?
à
1. Infect host Q: How do viruses achieve reproductive success?
à
1. Infect host 2. Reproduce within host Q: How do viruses achieve reproductive success?
à à
1. Infect host 2. Reproduce 3. Infect new host within host Q: How do viruses achieve reproductive success?
à à
1. Infect host 2. Reproduce 3. Infect new host within host Strategy 1: Reproduce rapidly within host Strategy 1: Reproduce rapidly within host ↓ ↑ Chance of infecting new host ↓ Host viability Strategy 1: Reproduce rapidly within host ↓ ↑ Chance of infecting new host ↓ Host viability
Strategy 2: Reproduce slowly within host Strategy 1: Reproduce rapidly within host ↓ ↑ Chance of infecting new host ↓ Host viability
Strategy 2: Reproduce slowly within host ↓ ↓ Chance of infecting new host ↑ Host viability Q: Why is HIV infection usually fatal?
Q: Why is HIV infection usually fatal?
A: Because the virus is “short- sighted”
Q: Why is HIV infection usually fatal?
A: Because the virus is “short- sighted”
- lethal strains predominate because of a short- term advantage in survival and reproduction.
Q: Why has a vaccine for HIV-1 not been successfully developed?
Q: Why has a vaccine for HIV-1 not been successfully developed?
A1: Because the virus evolves very rapidly.
Q: Why has a vaccine for HIV-1 not been successfully developed?
A1: Because the virus evolves very rapidly.
A2: Because of HIV-1 strain diversity.
Distribution of HIV-1 major clades The CCR5-Δ32 allele confers resistance to HIV infection