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 fishlike 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? 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

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 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.

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. 3. The belief in the immutability of species. 4. The belief in the unique position of man in creation.

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 What is AZT? HIV virus

Natural selection, AZT, and the What is AZT? HIV virus AZT (azidothymidine) is a base analogue.

Structure of azidothymidine

Natural selection, AZT, and the What is AZT? HIV virus 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 10 6 higher than ours!

How does HIV evolve so rapidly? 1. High mutation rate HIV s mutation rate is 10 6 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 10 6 higher than ours! 2. Short generation time 1 year 300 viral generations. 10 years of viral 2-3 x 10 6 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. 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

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 within host 3. Infect new 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 shortterm 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