Evolution
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Introduction
Historical context of evolution
Processes and mechanisms of evolution
Origin and evolution of life
Specific topics for discussion
Take-Home Messages
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Darwin: Voyage of the Beagle and the Origin of Species: the epitomy of
the scientific method
Mechanism: natural selection operates on genetic variation at the
level of populations and over time gradually changes the gene pool,
leading to microevolution (populations) and/or macroevolution
(species)
“As you sleep”, evolution is in action: GMO’s, pesticide resistance
in plants and animals, and antibiotic resistance in microbes
Theory of evolution extraordinarily provides the mechanism to
explain two sides of the same coin: diversity and similarity of living
systems
Theory of evolution is a gift of monumental importance in the life
sciences, and its importance has only grown since Darwin’s seminal
publication in 1859 (Origin of Species)
Introduction
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Two sides of the same coin: diversity and similarity
Theory of evolution
 Define theory of evolution
 Species evolve gradually from ancestral species
 Mechanism is natural selection
Gift to biology
 Unifying theory to explain diversity and similarity of
all living systems
 Impressive and substantial underpinning to the life
sciences (ecology, environmental sciences, genetic
engineering, astrobiology, etc.)
Historical Context: Darwin
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Voyage of the Beagle on the HMS
Beagle (1831)
 Age 22 as naturalist to
catalogue plants and animals
 Convention at the time: static
view (pre-ordained)
 Frame of reference for Darwin:
UK landscape and biodiversity
as bland as UK food
Notable Observations by Darwin
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South American diversity of
landscapes and biota
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Brazilian rainforest
Savannas of Argentina
Dry deserts of Terra del Fuego
Towering mountains of the Andes
Flora and fauna distinct from
Europe
Plethora of structures with
intuitive value in the
environment (adaptations)
Seeding of idea: living systems
are not static but vary as a
function of the environment
Observations (Galapagos)
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Galapagos Islands (seminal
event)
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Volcanic islands off Ecuador
and Peru
Fauna (birds, tortoises, plants,
etc.)
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Distinct lineage to species on S.
American mainland
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Finches
Tortoise
Seeding of idea:
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fauna arrived from mainland, then
Fauna diversified in new
environment
Darwin back to the UK (1836)
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Two seminal ideas in 1830’s
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Malthus: population growth exceeds available resources
Competition for limited resources (food, water, light, mates)
limits number of offspring
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maple tree produces 1000’s of seed of which ~ 10 germinate and grow
– 0.0001%)
Hypothesis:
Environment drives the origin of species via the gradual
accumulation of traits that incrementally improve survival
over time (centuries to millennia)
Darwin and Natural Selection (1840)
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Idea No. 1: Organisms differ in their success in
reproduction and therefore contribute
differently to future generations
Idea No. 2: Driving force for this differential
success is natural selection acting on the
variability among individuals
Product: Evolution of adaptations that enhance
success (fitness)
Darwin: Origin of Species (1859)
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Two principal tenets
Species evolve gradually from ancestral species
 Mechanism is natural selection
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Theory of Evolution as a gift to biology
Origin of diversity
 Origin of similarity
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Heads: Diversity
Tails: Similarity
Molecular Similarity/Dis-similartity
Number of amino
acid differences
among animals in
reference to humans
in the protein
hemoglobin
Human beta chain
0
Gorilla
1
Gibbon
2
Rhesus monkey
8
Dog
15
Horse, cow
25
Mouse
27
Gray kangaroo
38
Chicken
45
Frog
67
Lamprey
125
Sea slug (a mollusk)
127
Processes and Mechanisms
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Populations and species evolve (hierarchy)
Kingdom
Family
Species
Populations
Individuals
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Evolution at the population level is called
microevolution
Evolution at the species level is called macroevolution
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Concept of Fitness
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Fitness = relative contribution of an individual to
the next generation
Positive fitness
 Negative fitness
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Contrast fitness to “survival of the fittest” and
“struggle for survival”
Variation in Fitness
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Organisms vary in their morphology, physiology
and biochemistry
Source of variation is genetics (yet to be
discovered)
Inheritance of traits by Mendel (1860’s)
 DNA structure by Watson and Crick (1950’s)
 Gene sequences (1970’s)
 Genetic engineering (2000’s)
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Summary of Mechanism (1940’s)
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Two cardinal tenets
 Natural
selection (Darwin)
 Individuals differ genetically (Mendel)
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Result:
gene pool of the next generation is a
consequence of the action of natural
selection on inherited variation at the level of
populations
First Generation
Gene Pool
Selection
Fitness
Gene Pool
Second Generation
Gene Pool
N>100 Generations
Gene Pool
N>1000 Generations
Gene Pool
Microevolution
Macroevolution
Large-Scale Changes: Global
Selective Agents
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Progressive
physical/chemical changes
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Catastrophic climate change
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Carbon dioxide in the
atmosphere
Oxygen in the atmosphere
Breakup of Pangeae
Asteroid impacts (dinosaurs
followed by mammals)
Instantaneous biological
changes
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Evolution of enzymes
Origin and Evolution of Life on Earth
Origin of Life in the Universe:
Astrobiology
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Chemicals of life
 Information brokers: nucleic acids and nucleotides
 Carbohydrates (carbon skeletons for polymers)
 Lipids (e.g., membranes)
 Proteins (e.g., enzymes)
Medium for life is water (H2O)
Elements for life are common in the Universe
Probability: extremely high probability that life has
originated and evolved elsewhere in the Universe at
multiple times
Panspermia: hypothesis that life on Earth originated
elsewhere in the Universe
Panspermia
Origin and Evolution of Life: Classification
Domain
Bacteria
Domain
Archaea
Common Ancestor
(4 - 4.5 Billion Years Ago)
Domain
Eukarya
Classification of Life on Earth
Illustration of a Virus
Figure 24.28
24-519
Some Common Viruses
Virus
HIV
Influenza
Ebola virus
Influenza virus
Smallpox
Some forms of cancer
Colds
Polio
HIV
Evolution of Humans
Evolution in Action “As You Sleep”
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Antibiotic resistance in
microbes
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100+ antibiotics since 1940’s
(penicillium)
Efficacy of antibiotics
Resistance to insecticides in
cockroaches
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“Godzilla the Cockroach”
Evolution While You Sleep
Industrial melanism in
the peppered moth in
UK
Peppered Moth
pollution as stress
followed by
selection predation
by birds
Melanic Peppered Moth
Evolution As You Sleep
Genetically Modified
Organisms (GMO’s)
Cotton plants
engineered for frost
resistance with DNA
insert (Bt gene) from
a bacterium