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Lecture #1 – Darwinian Evolution
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Key Concepts:
• Evidence for evolution
• Darwin’s theory
• The Modern Synthesis
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Spiritual vs. Intellectual
Different, but not necessarily in conflict
The human emotional experience
The human intellectual experience
“The Bible tells us how to go to Heaven, not how the heavens go”3
Galileo
Reality Check:
The world’s major religions and the dominant
religion in the world’s four most populous countries
Religious
Affiliation
World
China
India
United
States
8
6
82
Muslim
33
21
2
14
2
13
77
Nonbelievers
14
50
1
12
2
Hindu
13
12
6
~0
~0
73
1
3
32
6
1
4
9
1
1
1
~0
~0
2
~0
Christian
Other
Buddhist
Jewish
SOURCE – National Geographic, December 2007
Indonesia
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There are many equally valid ways
“to go to Heaven”
• We rely on our religious texts for moral,
emotional and spiritual guidance
• We rely on science and other intellectual
pursuits to gain knowledge about the
natural world
There need be no conflict in these different
ways of thinking and learning
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Defining Evolution:
• A process of change over time
• Cannot deny that this occurs
• Evidence is overwhelming:
Historical – within the span of recorded
human history
Fossils – the very long term geological record
Comparative morphology and anatomy
Biogeography – the geographic distribution of
species
The unity of life
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Historical Evidence: observed character
displacement
Changes in beak size recorded over about 2 decades
after a natural migration event
Image – finches on the Galapagos
Resident species shifted
to smaller beak size
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Photographs by B. Rosemary Grant/Science, 2006
Big-beaked invader
All of agriculture is based on
human selection events
• The domestication of
grass ~12,000 years ago
• Led to the first cultural
shift in human civilization
Image – wheat
Nomadic hunter-gather
tribes  villages based
on agricultural production
• Other plants and
animals as well….
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Artificial Selection – Brassica
oleracea in all its forms
Image – cabbage, kale, cauliflower, broccoli, Brussels sprouts
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Farm Animals – different breeds
Images – different
breeds of cattle and
chickens
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Cats and Dogs
A great dane is the same species as a toy poodle!
Images – different
breeds of cats and
dogs
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The development of pesticide
resistance
• Resistance to
insecticides,
herbicides,
antibiotics…..
• All natural responses
to human generated
changes in the
environment
Diagram – development
of pesticide resistance
due to use of insecticides
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Defining Evolution:
• A process of change over time
• Cannot deny that this occurs
• Evidence is overwhelming:
Historical – within the span of recorded
human history
Fossils – the very long term geological record
Comparative morphology and anatomy
Biogeography – the geographic distribution of
species
The unity of life
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The fossil record extends back
BILLIONS of years
Images – fossils of plants and fish
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Most form in marine sediments
Diagram – formation of sedimentary rocks with fossils embedded
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Fossil substrates – can you think of others???
Images – other fossil substrates
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Formation of sedimentary rocks is
not uniform in time or space
Same diagram as #15
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Critical Thinking
• The formation of sedimentary rocks is not
uniform in time or space
• Why not???
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Critical Thinking
• The formation of sedimentary rocks is not
uniform in time or space
• Why not???
• Dynamic processes!
Geological activity
Climate
Depositional environments
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Formation of sedimentary rocks is
highly dynamic
• Varies with geological activity
Tectonic movements, mountain building,
erosion
Varies with climate
Rain, wind, freeze/thaw cycles, water
temperature – all affect erosion and
sedimentation
• Varies with the depositional environment
Finer sediments in still water, coarser
sediments with more wave action or other
energy
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The earth’s crust is very dynamic
Diagram – dynamic geological processes:
tectonic movements, mountain building, erosion
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Formation of sedimentary rocks is
highly dynamic
• Varies with geological activity
Tectonic movements, mountain building,
erosion
• Varies with climate
Rain, wind, freeze/thaw cycles, water
temperature – all affect erosion and
sedimentation
• Varies with the depositional environment
Finer sediments in still water, coarser
sediments with more wave action or other
energy
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Climate is naturally dynamic on
a geological time scale
Graph – benthic carbonates; analogous
to climate change over the past 5
million years
Benthic carbonates parallel atmospheric
temperature changes
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Critical Thinking
• How could water temperature affect the
formation of sedimentary rocks???
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Critical Thinking
• How could water temperature affect the
formation of sedimentary rocks???
• Limestone is a sedimentary rock that is
formed from the tiny shells of marine
organisms
• The abundance of these organisms is
partially dependent on water temperature
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Formation of sedimentary rocks is
highly dynamic
• Varies with geological activity
Tectonic movements, mountain building,
erosion
• Varies with climate
Rain, wind, freeze/thaw cycles, water
temperature – all affect erosion and
sedimentation
• Varies with the depositional environment
Finer sediments in still water, coarser
sediments with more wave action or other
energy – WHY???
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Play with the “ocean”
• In high energy environments (waves) only
the heaviest sediments can settle
Coastal environments produce sandstones
• In off-shore environments (no waves) finer
sediments can settle
Off-shore environments produce siltstones,
slates, limestones…
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Sediment size depends on the energy level at
the site of deposition
Diagram of different depositional environments
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Formation of sedimentary rocks is
highly dynamic
• THUS sediments tend to be deposited in
identifiable layers
• THUS organisms trapped in sediments
form a time sequence
The earliest organisms are in the bottom
layers and the most recent organisms in the
upper layers
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The Grand Canyon – a time sequence
Image – the Grand Canyon
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Formation of sedimentary rocks is
highly dynamic
• THUS sediments tend to be deposited in
identifiable layers
• THUS organisms trapped in sediments
form a time sequence
The earliest organisms are in the bottom
layers and the most recent organisms in the
upper layers
Dating these fossils reveals the history of
change
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Study the
geological time
scale – it’s the
history of life on
earth!
The geological time scale
Use a search
engine to find the
geological time
scale
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Of course the fossil record is
incomplete!
• Organisms must be trapped in the right
place under the right conditions – a rare
event
• Fossils must survive geological processes
such as subduction, metamorphosis and
erosion
• Fossils must be found!
Have you ever found a fossil???
• But what we do have is irrefutable evidence
of change over time
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Fossil Evidence Shows Progression
Over Time – new species….
Diagram – evolution of elephant lineages
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….new traits….
Diagram – limbs developing from bony fins in tetrapods
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….transitional forms….
Diagram – transition from bony fins to limbs
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Defining Evolution:
• A process of change over time
• Cannot deny that this occurs
• Evidence is overwhelming:
Historical – within the span of recorded
human history
Fossils – the very long term geological record
Comparative morphology and anatomy
Biogeography – the geographic distribution of
species
The unity of life
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Comparative morphology – homologous
structures are derived from a common ancestor
Diagram – forelimbs of various mammals
showing identical bone structure with
variation in bone size
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Fish SalamanderTortoise Chicken Pig
Cow
Rabbit
Human
Stage of
Development
Early
Diagram – similarities in the embryos of a
wide variety of vertebrates
Later
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Strickberger, 1996
Images – orchid floral structure
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Comparative morphology –
vestigial traits
• Structures that are physically or
functionally reduced but clearly similar to
functional structures in related organisms
Tiny limb bones in some snakes and aquatic
mammals
Non-flying wings in ostriches emus, kiwis,
penguins
Blind eyes in cave-dwelling animals
Vestigial tails in humans
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Defining Evolution:
• A process of change over time
• Cannot deny that this occurs
• Evidence is overwhelming:
Historical – within the span of recorded
human history
Fossils – the very long term geological record
Comparative morphology and anatomy
Biogeography – the geographic distribution of
species
The unity of life
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Biogeography – Darwin observed patterns
of species distribution during his voyage
on the Beagle
Diagram – the voyage of the Beagle
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Sloths – found only in South America, even though
similar habitats exist on other continents
Image – modern and fossil sloths
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Marsupials – almost restricted to Australia
…though convergent evolution has resulted in many
similar eutherian mammals on other continents
Diagram of marsupial and eutherian mammals showing similar forms
Convergent evolution –
similar traits in unrelated
organisms that evolved
under similar selection
pressures….more later
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The Galápagos and other volcanic islands
Many closely related endemic species….that are
similar to those found on the closest mainland
Darwin’s conclusion – species migrated and
evolved new adaptations in their new home
Diagram of Darwin’s finch lineages
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Defining Evolution:
• A process of change over time
• Cannot deny that this occurs
• Evidence is overwhelming:
Historical – within the span of recorded
human history
Fossils – the very long term geological record
Comparative morphology and anatomy
Biogeography – the geographic distribution of
species
The unity of life
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Uniformity and Diversity:
same DNA, same ATP, same amino
acids, same membranes, same
aerobic respiration….
Image – frog in the center of a bromeliad
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Critical Thinking
• What is the implication of this uniformity in
the basic building blocks of life, even
though there are many millions of
organisms both extant and extinct???
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Critical Thinking
• What is the implication of this uniformity in
the basic building blocks of life, even
though there are many millions of
organisms both extant and extinct???
• These structures and processes emerged
at the very beginning of life on this planet
and have been conserved in all organisms
throughout evolutionary history
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Defining Evolution:
• A process of change over time
• Cannot deny that this occurs
• Evidence is overwhelming:
Historical – within the span of recorded
human history
Fossils – the very long term geological record
Comparative morphology and anatomy
Biogeography – the geographic distribution of
species
The unity of life
Step 1: accepting that evolution occurs….Step 2:
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HOW???
Historical Context
The development of ideas about biological evolution
and the age of the earth began in the 1700’s –
Darwin was just the first to publish!
Timeline – the development of thought on evolution
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Darwin’s voyage on the Beagle, 18311836…..publication of his theory, 1859
Map – the voyage of the Beagle
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Darwin’s Theory of Evolution by Natural
Selection
based on observation + logical inference
• OBSERVATION #1 – all species have the reproductive
potential for exponential population growth
• OBSERVATION #2 – populations tend to remain stable
OBSERVATION #3 – environmental resources are limited
 INFERENCE #1 – excess of offspring leads to a struggle for
existence
• OBSERVATION #4 – significant variation exists between
individuals of the same species
• OBSERVATION #5 – some variation is heritable
 INFERENCE #2 – individuals that are best adapted to their
environment contribute more offspring to the next generation =
differential reproductive success = Darwin’s natural selection
 INFERENCE #3 – TIME X CHANGE = DIVERSITY
Don’t panic – this is just a summary slide for you to look at later
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Observation #1: All species have the
potential for exponential population growth
Images – examples of high reproductive potential in various organisms
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Observation #2:
Populations tend to
remain stable
(though sometimes within a fluctuating range)
not exponential
Graphs – examples of
actual population growth
patterns
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Observation #3: Environmental
resources are limited
Image – lynx chasing rabbit
food….
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water….
Image – desert landscape
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habitat….
Images – various animals in habitat
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Inference #1: Excess offspring in a
resource-limited environment leads to a
“struggle for existence”
Image – resource competition between aquatic plants
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Observation #4: Variation exists in all
natural populations
Diagram – natural variation in beetles
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Image – natural variation in plants
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Image – natural variation in mollusks
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Images – natural variation in humans
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Observation #5: Some variation is heritable
Images – heritable variation in various animals
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Inference #2: Best adapted individuals
reproduce the most
Differential Reproductive Success!!!
Image – polar bears fighting
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Inference #3: Darwin’s Big One
Over long periods of time and many
generations the incremental results of
differential reproductive success will
lead to divergence between
populations in different environments
and eventually to the development of
new species
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Key Conclusion
Small changes over long periods of time result
in adaptations to different environments and to
the emergence of new species
Image – orchid mantis
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Same as #68
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Same as #68
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Images – additional cryptic animals; through slide #78
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Critical Thinking
• What other testable explanation is there
for an insect or other animal that evades
predation by mimicking its habitat???
• How else might this cryptic form and
coloration benefit the animal???
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Critical Thinking
• What other testable explanation is there
for an insect or other animal that evades
predation by mimicking its habitat???
None
• How else might this cryptic form and
coloration benefit the animal???
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Critical Thinking
• What other testable explanation is there
for an insect or other animal that evades
predation by mimicking its habitat???
None
• How else might this cryptic form and
coloration benefit the animal???
More likely to catch their own prey items
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Darwin originally predicted gradual
speciation from a common ancestor…..
• Now we know
that abrupt
changes are also
possible
• Also, some
gradual changes
may not be
recorded in the
fossil record
Diagram – mammal lineages
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Questions Remain
• We don’t, and may never, know exactly
how life originated on this planet
• But we do have a pretty good explanation
for how diversity developed and why
diversity changes over time
Conditions change
Organisms adapt
Images – more cryptic animals; same on next slide
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Questions Remain
• We don’t, and may never, know exactly
how life originated on this planet
• But we do have a pretty good explanation
for how diversity developed and why
diversity changes over time
Conditions change
Organisms adapt
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The Modern Synthesis
• Darwin’s concepts of natural selection and
differential reproductive success leading to
adaptations and speciation
• Mendel’s work on heredity and hypothesis of
a particulate method of hereditary transfer
• Microscopic revelation of chromosomes as
that particle in the late 1800’s – early 1900’s
• Discovery of the structure of the DNA
molecule in the early 1950’s
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The Theory of Evolution
A comprehensive body of knowledge
that describes a known fact of nature
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Key Concepts:
• Evidence for evolution
• Darwin’s theory
• The Modern Synthesis
Questions???
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