Darwin’s Theory of Evolution
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Transcript of Darwin’s Theory of Evolution
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DARWIN’S THEORY OF EVOLUTION
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Organisms Change Over Time
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Common Descent with Modification
Darwin proposed that organisms descended from common ancestors
Idea that organisms change with time, diverging from a common form
Caused evolution of new species
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Natural Selection Driving force for
evolution During the
struggle for resources, strongest survive & reproduce
Idea that at least some of the differences between individuals, which impact their survival and fertility, are inheritable
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ORIGIN OF SPECIES
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Darwin Presents His Case
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Publication of “On The Origin of Species”
Upon His Return To England, Darwin Developed His Observations Into The Theory of Evolution
But He Did Not Publish For 25 Years –
Why?
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Publication of “On The Origin of Species”
Darwin Knew That His Theory Would Be Extremely Controversial And Would Be Attacked
His Theory Challenged Established Religious & Scientific Beliefs, Particularly About The Creation Of Man
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Publication of “On The Origin of Species”
He Refused To Publish Until He Received An Essay From Alfred Wallace Fellow Naturalist Independently
Developed The Same Theory
After 25 Years, Someone Else Had Come To The Same Conclusions From Their Observations Of Nature
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Wallace’s Contribution
• Alfred Russel Wallace Independently came to same Conclusion as Darwin that species changed over time because of their struggle for existence
• When Darwin read Wallace’s essay, he knew he had to publish his findings 8
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Publication of “On The Origin of Species”
Darwin Presented Wallace’s Essay & Some Of His Work At A Scientific Conference of the Linnaean Society in July of 1858
Then He Started On his book “Origin of Species”
It Took Darwin 18 Months To Complete The Book
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Natural Variation and Artificial Selection
Abandoned The Idea That Species Were Perfect & Unchanging
Observed Significant Variation in All Species Observed
Observed Farmers Use Variation To Improve Crops & Livestock
Called Selective Breeding
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Natural Variation and Artificial Selection
Natural VariationDifferences Among
Individuals Of A Species Artificial Selection
Selective Breeding To Enhance Desired Traits Among Stock or Crops
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Natural Variation and Artificial Selection
Key Concept:In Artificial Selection, Nature Provided The Variation Among Different Organisms, And Humans Selected Those Variations That They Found Useful
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ORIGIN OF SPECIES
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Concepts and Controversy
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Evolution By Natural Selection Concepts
The Struggle for Existence (compete for food, mates, space, water, etc.)
Survival of the Fittest (strongest able to survive and reproduce)
Descent with Modification (new species arise from common ancestor replacing less fit species)
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Survival of the Fittest Fitness
Ability of an Individual To Survive & Reproduce
Adaptation Inherited Characteristic That
Increases an Organisms Chance for Survival
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Survival of the Fittest Adaptations Can Be:
Physical Speed, Camouflage, Claws, Quills, etc.
Behavioral Solitary, Herds, Packs, Activity, etc.
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Survival of the Fittest Fitness Is Central To The
Process Of Evolution Individuals With Low Fitness
DieProduce Few Offspring
Survival of the FittestAKA Natural Selection
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Survival of the FittestKey Concept
Over Time, Natural Selection Results In Changes In The Inherited Characteristics Of A Population. These Changes Increase A Species Fitness In Its Environment
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Natural Selection Cannot Be Seen Directly It Can Only Be Observed As
Changes In A Population Over Many Successive GenerationsRadiationFossil Record
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Descent With Modification Takes Place Over Long
Periods of Time Natural Selection Can Be
Observed As Changes InBody StructuresEcological NichesHabitats
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Descent With Modification Species Today Look Different
From Their Ancestors Each Living Species Has
DescendedWith ChangesFrom Other SpeciesOver Time
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Descent With Modification
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Descent With Modification Implies
All Living Organisms Are Related
Single Tree of Life DNA, Body Structures, Energy Sources
Common DescentAll Species, Living & Extinct,
Were Derived From Common Ancestors
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Major Problem in Darwin’s Theory
• No mechanism to explain natural selection
• How could favorable variations be transmitted to later generations?
• With the rediscovery of Mendel’s work in the first half of the 20th century, the missing link in evolutionary theory was found 25
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Opposition to Evolution• The upheaval
surrounding evolution began with Darwin’s publication of On the Origin of Species By Means of Natural Selection
• The debate continues nearly 150 years later
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THEORY OF EVOLUTION TODAY
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Supporting Evidence
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Homologous Structures
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Evidence for Evolution - Comparative Embryology
Similarities In Embryonic Development
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Evolution of
pesticide resistanc
e in response
to selection
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Evidence for Evolution – Evolution Observed
Evolution of drug-resistance in HIV
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Evidence for Evolution – Evolution Observed
Selection against small guppies results in an increase in average size
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Evolutionary Time Scales
Macroevolution: Long time scale events
that create and destroy species.
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Microevolution:
Short time scale events
(generation-to-generation) that
change the genotypes and phenotypes of
populations
Evolutionary Time Scales
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Evidence of EvolutionKey Concept
Darwin Argued That Living Things Have Been Evolving On Earth For Millions of Years. Evidence For This Process Could Be Found In:
The Fossil RecordThe Geographical Distribution of
Living SpeciesHomologous Structures of Living
OrganismsSimilarities In Early Development
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Fossil Record Earth is Billions of Years Old Fossils In Different Layers of Rock
(sedimentary Rock Strata) Showed Evidence Of Gradual Change Over Time
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Geographic Distribution of Living Species
Different Animals On Different Continents But Similar Adaptations To Shared Environments
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Homologous Body Structures
Scientists Noticed Animals With Backbones (Vertebrates) Had Similar Bone Structure
May Differ In Form or Function
Limb Bones Develop In Similar Patterns
Arms, Wings, Legs, Flippers
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Homologous Body Structures
Structures That Have Different Mature Forms But Develop From The Same Embryonic Tissues
Strong Evidence That All Four-Limbed Animals With Backbones Descended, With Modification, From A Common Ancestor
Help Scientist Group Animals
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Homologous Body Structures
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Homologous Body Structures
Not All Serve Important Functions Vestigial Organs
Appendix In Man Legs On Skinks
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Similarities In Early Development
Embryonic Structures Of Different Species Show Significant Similarities
Embryo – early stages of vertebrate development
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Human Fetus – 5 weeks
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Chicken Turtle
Rat
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Review
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Darwin's Theory1. Individual Organisms In Nature
Differ From One Another. Some Of This Variation Is Inherited
2. Organisms In Nature Produce More Offspring Than Can Survive, And Many Of These Offspring Do No Reproduce
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Darwin's Theory3. Because More Organisms Are
Produced Than Can Survive, Members Of Each Species Must Compete For Limited Resources
4. Because Each Organism Is Unique, Each Has Different Advantages & Disadvantages In The Struggle For Existence
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Darwin's Theory5. Individuals Best Suited To Their
Environment Survive & Reproduce Successfully – Passing Their Traits To Their Offspring.
6. Species Change Over Time. Over Long Periods, Natural Selection Causes Changes That May Eventually Lead To New Species
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Darwin's Theory7. Species Alive Today Have Descended
With Modifications From Species That Lived In The Past
8. All Organisms On Earth Are United Into A Single Tree Of Life By Common Descent
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