1 lecture #1 – darwinian evolution. 2 key concepts: evidence for evolution darwin’s theory the...
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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”Galileo
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Reality Check:The world’s major religions and the dominant
religion in the world’s four most populous countries
Religious Affiliation
World China IndiaUnited States
Indonesia
Christian 33 8 6 82 13Muslim 21 2 14 2 77
Non-believers 14 50 1 12 2
Hindu 13 ~0 73 1 3
Other 12 32 6 1 4
Buddhist 6 9 1 1 1
Jewish ~0 ~0 ~0 2 ~0
SOURCE – National Geographic, December 2007
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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 recordComparative morphology and anatomyBiogeography – the geographic distribution of
speciesThe unity of life
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Image – finches on the Galapagos
Photographs by B
. Rosem
ary Grant/S
cience, 2006Historical Evidence: observed character
displacement Changes in beak size recorded over about 2 decades
after a natural migration event
Big-beaked invader
Resident species shifted to smaller beak size
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Image – wheat
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 civilizationNomadic hunter-gather
tribes villages based on agricultural production
• Other plants and animals as well….
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Image – cabbage, kale, cauliflower, broccoli, Brussels sprouts
Artificial Selection – Brassica oleracea in all its forms
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Images – different breeds of cattle and chickens
Farm Animals – different breeds
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Images – different breeds of cats and dogs
Cats and DogsA great dane is the same species as a toy poodle!
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Diagram – development of pesticide resistance due to use of insecticides
The development of pesticide resistance
• Resistance to insecticides, herbicides, antibiotics…..
• All natural responses to human generated changes in the environment
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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 recordComparative morphology and anatomyBiogeography – the geographic distribution of
speciesThe unity of life
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Images – fossils of plants and fish
The fossil record extends back BILLIONS of years
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Diagram – formation of sedimentary rocks with fossils embedded
Most form in marine sediments
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Images – other fossil substrates
Fossil substrates – can you think of others???
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Same diagram as #15
Formation of sedimentary rocks is not uniform in time or space
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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 activityClimateDepositional environments
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Formation of sedimentary rocks is highly dynamic
• Varies with geological activityTectonic movements, mountain building,
erosionVaries with climateRain, wind, freeze/thaw cycles, water
temperature – all affect erosion and sedimentation
• Varies with the depositional environmentFiner sediments in still water, coarser
sediments with more wave action or other energy
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Diagram – dynamic geological processes:tectonic movements, mountain building, erosion
The earth’s crust is very dynamic
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Formation of sedimentary rocks is highly dynamic
• Varies with geological activityTectonic movements, mountain building,
erosion
• Varies with climateRain, wind, freeze/thaw cycles, water
temperature – all affect erosion and sedimentation
• Varies with the depositional environmentFiner sediments in still water, coarser
sediments with more wave action or other energy
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Graph – benthic carbonates; analogous to climate change over the past 5 million years
Climate is naturally dynamic on a geological time scale
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 activityTectonic movements, mountain building,
erosion
• Varies with climateRain, wind, freeze/thaw cycles, water
temperature – all affect erosion and sedimentation
• Varies with the depositional environmentFiner 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 settleCoastal environments produce sandstones
• In off-shore environments (no waves) finer sediments can settleOff-shore environments produce siltstones,
slates, limestones…
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Diagram of different depositional environments
Sediment size depends on the energy level at the site of deposition
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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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Image – the Grand Canyon
The Grand Canyon – a time sequence
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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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The geological time scale
Study the geological time scale – it’s the
history of life on earth!
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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Diagram – evolution of elephant lineages
Fossil Evidence Shows Progression Over Time – new species….
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Diagram – limbs developing from bony fins in tetrapods
….new traits….
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Diagram – transition from bony fins to limbs
….transitional forms….
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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 recordComparative morphology and anatomyBiogeography – the geographic distribution of
speciesThe unity of life
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Diagram – forelimbs of various mammals showing identical bone structure with variation in bone size
Comparative morphology – homologous structures are derived from a common ancestor
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Diagram – similarities in the embryos of a wide variety of vertebrates
FishSalamanderTortoiseChickenPig Cow Rabbit Human
Strickberger, 1996
Stage of Development
Early
Later
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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 organismsTiny limb bones in some snakes and aquatic
mammalsNon-flying wings in ostriches emus, kiwis,
penguinsBlind eyes in cave-dwelling animalsVestigial 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 recordComparative morphology and anatomyBiogeography – the geographic distribution of
speciesThe unity of life
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Diagram – the voyage of the Beagle
Biogeography – Darwin observed patterns of species distribution during his voyage
on the Beagle
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Image – modern and fossil sloths
Sloths – found only in South America, even though similar habitats exist on other continents
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Diagram of marsupial and eutherian mammals showing similar forms
Marsupials – almost restricted to Australia
…though convergent evolution has resulted in many similar eutherian mammals on other continents
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 recordComparative morphology and anatomyBiogeography – the geographic distribution of
speciesThe unity of life
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Image – frog in the center of a bromeliad
Uniformity and Diversity:same DNA, same ATP, same amino
acids, same membranes, same aerobic respiration….
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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 recordComparative morphology and anatomyBiogeography – the geographic distribution of
speciesThe unity of life
Step 1: accepting that evolution occurs….Step 2:HOW???
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Timeline – the development of thought on evolution
Historical ContextThe development of ideas about biological evolution
and the age of the earth began in the 1700’s – Darwin was just the first to publish!
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Map – the voyage of the Beagle
Darwin’s voyage on the Beagle, 1831-1836…..publication of his theory, 1859
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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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Images – examples of high reproductive potential in various organisms
Observation #1: All species have the potential for exponential population growth
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Graphs – examples of actual population growth patterns
Observation #2: Populations tend to
remain stable(though sometimes within a fluctuating range)
not exponential
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Image – lynx chasing rabbit
Observation #3: Environmental resources are limited
food….
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Image – desert landscape
water….
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Images – various animals in habitat
habitat….
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Image – resource competition between aquatic plants
Inference #1: Excess offspring in a resource-limited environment leads to a
“struggle for existence”
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Diagram – natural variation in beetles
Observation #4: Variation exists in all natural populations
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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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Images – heritable variation in various animals
Observation #5: Some variation is heritable
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Image – polar bears fighting
Inference #2: Best adapted individuals reproduce the most
Differential Reproductive Success!!!
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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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Image – orchid mantis
Key Conclusion
Small changes over long periods of time result in adaptations to different environments and to
the emergence of new species
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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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Diagram – mammal lineages
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
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Images – more cryptic animals; same on next slide
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 timeConditions changeOrganisms adapt
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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 timeConditions changeOrganisms 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 EvolutionA 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???