Pal Chap 5 Evolution
Transcript of Pal Chap 5 Evolution
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EVOLUTION
The Principle of Evolution
z Living things have evolved through time in anorderly fashion, without repetition and withoutreversal, to produce modern life. OR
z All existing life has its origins in pre-existing
life and has changed to its present state
through successive generations.
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Contributing Concepts
to Evolution
z Lucretius 96-55 BC
Universe-shower of atoms with eddies
Nature in a constant state of change, growth,deathspecies change with time
z Read by scholars in spite of conflict withBible
z Note conflict with Creationists universemade all at once then decay
Concepts Contributing to Darwin'sEvolution
z Exploration of the world in 1700s
World too large for biblical accounts
Too many animals for the ark
Animals (and plants) differ markedly in different parts of the
world
z
Linneuss books Huge number of living things
Living things are naturally related to one another
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Contributing Concepts
to Evolution
z Geology William Smith
z Studied fossils of England
z Developed the Law of Fossil Succession
Fossils succeed one another in an orderly fashionthrough time
New forms appear as time passes not all atonce
Flood (s) dont explain it
Concepts Contributing to Darwin'sEvolution
z Geology
James Hutton and Charles Lyell
Geologic Time and Uniformitarianism
z The earth is very, very old (more than 6000 yrs.)
z Present day processes explain past changes in rocks
(and fossils)
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Concepts Contributing to Darwin's
Evolution
Count Buffon (1707-1788)
The Ladder of Creation Theorized thetransmutation of species into one another
Simple to complex with man at top but belowangels and God.
Still accepted by some; was accepted by
Thomas Jefferson
Ladder of Creation
z Depends on spontaneous generation
z Each group evolves parallel to others
z Problems:
Fossil record not a picture of simple to complex
Cambrian Explosion Spontaneous generation disproved by Louis
Pasteur
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Concepts Contributing to Darwin's
Evolution
z Jean Baptiste Lamark (1744-1829) Inheritance of acquired characteristics
Characteristics acquired during organismslifetime can be passed on, inherited.
Life evolved by accumulation of
acquired characters
Inheritance of AcquiredCharacteristics
z Problems
August Weismann (1834-1914 experimentsproved it isnt so with mice
James Watson (1928-) described a one-wayrelationship between DNA and RNA
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Concepts Contributing to Darwin's
Evolution
z Georges Cuvier (1769-1832)
z Catastrophism: Catastrophies explained extinctionsand new creations
z Unconformities were evidence of catastrophies
z Problems:
Extinctions didnt always correspond to unconformities New forms arose between unconformities
Concepts Contributing to Darwin'sEvolution
z Erasmus Darwin (1731-1802)
z Poem on Evolution
Evolution of all life from a singleancestor
Like a branching tree
z Problem
Lacking a mechanism for speciation
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Concepts Contributing to Darwins
Evolution
z Thomas Malthus (1766-1834)
Many more are born than survive
Individuals in a population compete forlimited resources
Evolution by Means of NaturalSelection
Alfred Russel Wallace(1823-1913)
Charles Darwin (1809-1882)
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Darwins Evidence in Origin of
Species
z Domestic selective breeding
z Natural adaptation to the environment
z Natural variation within populations
z Malthusian population and competition
z Fossils
z
Geographic distribution of speciesz Linnaeuss taxonomy
Darwins Evidence
z Domestic animals and selective breeding
Produces new forms like new varieties
The boundaries between varieties and speciesare blurred.
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Darwins Evidence
z Adaptation to the environment
Animals are physically and behaviorally adaptedto their immediate environments
Darwins finches
Diversification of
island life
Darwins evidence
z Variation within Populations Variations occur in all species
The boundary between species, sub-species andvarieties is blurred
Variations can be selected for (as in domesticselective breeding)
Variations become species in islands bydiversification into different environments
Variations can become new species characters
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Darwins Evidence
z Many more are born than survive
Competition must determine which survive
z Fossil Records show species arising andbecoming extinct (although imperfect recordof gradual change)
Darwins Evidence
z Geographic distribution
Species in proximity show closer relationships to each other
than to more geographically distant relatives.
Islands near continents are populated with species closelyrelated to those on the adjacent continent
Species are not randomly distributed around the world as a
creator would have made them
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Darwins Evidence
z The natural system of classification (Linneantaxonomy) reflects a belief in descent.
Genera and Families imply that their membersare descended from common ancestors (acommon ancestor)
Evolution is an underlying principle of taxonomy
Darwins Conclusions
z Natural Selection
z Evolution
z Phyletic Gradualism
z Cladism
z Competition
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Darwins Conclusions
z Natural Selection Organisms that inherit favorablevariations for their immediate environment will tendto survive more often than others (and reproduce). Traits appear in a population
Nature selectively acts on individuals with that trait todestroy or perpetuate
If favorable, trait spreads to whole population making achange toward new variety or species
Traits add up
Darwins Conclusions
z Evolution
Life has changed constantly through time
New species have arisen and species havebecome extinct
This occurs because of natural selection acting on
variations within populations
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Darwins Conclusions
z Phyletic Gradualism
The change from one species to another is agradual process
If change in the fossil record seems abrupt it isbecause the record is so imperfect.
Darwins Conclusions
z Cladism
Similar organisms aredescended from a singleancestor
Evolution is like a branching
tree
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Neodarwinism
z Mutation Changes in the genotype that produce changes in
the phenotype
Most mutations are detrimental to the phenotype,but not all.
z Population Genetics Mathematics show natural selection could make
major changes in the gene pool even with lowrates of mutation.
The 4 ISMs of Neodarwinism
z Reductionism
z Panselectionism
z Extrapolationism
z Gradualism
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Panselectionism
z While recognizing the importance of random drift forsilent mutations, selectionists hypotheses arguethat balancing and positive selection are the drivingforces of molecular evolution. Those hypotheses areoften based on the broader view calledpanselectionism, the idea that selection is the onlyforce strong enough to explain evolution, relaying
random drift and mutations to minor roles.
Panselectionism
z Natural selection is a continuously operatingforce that acts on all traits of the phenotype(hence all genes)
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Panselectionism
z All changes in the population are adaptive insome way
z All traits of the species are adaptive in someway
Panselectionism
z Nothing is neutral or wasted
The lions archetypal roar is used to communicate withother group members and warn intruders of territorial
boundaries.Long, retractable claws help the lion to grab and hold
prey.The species rough tongue helps it to peel the skin ofprey animals away from flesh and flesh away from
bone.Loose belly skin allows the African lion to be kicked by
prey with little chance of injury.
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Extrapolationism
z Part of Microevolution
Small changes seen in modern populations (suchas fruit flies) can be extrapolated to explain allmajor evolutionary change
Small changes add up to create larger changes
Microevolution is evolution on a small scalewithin asingle population. That means narrowing our focus toone branch of the tree of life.
Extrapolationism
z Microevolution
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Phyletic Gradualism
z Phyletic gradualism is a speciationhypothesis rooted in uniformitarianism. Thehypothesis states that species continue toadapt to new environmental and biologicalselection pressures over the course of theirhistory, gradually becoming new species
Gradualism
z Part of Microevolution
Evolution takes place gradually by theaccumulation of small steps that add up to largerchanges.
Numerous transitional stages should be
observable in evolution from one species toanother
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Gradualism: A long time ago, there were a lot of tiger-like animals, but withoutstripes. Most of them were unmarked, but a few had light markings and color
variation in their fur. These few blended in with the tall grasses a little bit better,so they were generally able to catch more food, and fewer of the marked than
unmarked ones died of hunger, so more of them were able to reproduce. In thenext generation, more animals were marked than in the previous generation. Ofthose that were marked, some had more, some less, and some the same amountof marks than in the previous generation. Also, the marks were more, less, or thesame amount clearly defined. Again, the ones with marks did better than the ones
without, and the ones with more, clearly defined marks did better than the oneswith fewer or fainter marks. Very gradually, over many, many generations, stripes
over the tigers' whole bodies formed and appeared in the whole population,because the tigers that survived in each generation were those whose marks weremost clear and contrasted most with the rest of the fur, and those that covered the
most area on the bodies of the tigers.
Challenges to Neodarwinism
z New Lamarkian Ideas
z Neutralism
z Types of Strange Genes
z Macroevolution
z Evolution and Paleontologyz New Theory of Evolution Punctuated
Equilibrium
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New Lamarkian Ideas
z Genetic assimilation shock orenvironmental stimulus seems to causegenetic change
z Experiential genes immunity inheritance
z Jumping genes and viruses
Jumping genes
z Transposons are sequences of DNA that can movearound to different positions within the genome of asingle cell, a process called transposition. In theprocess, they can cause mutations and change theamount of DNA in the genome. Transposons werealso once called jumping genes, and are examplesof mobile genetic elements. They were discovered
by Barbara McClintock early in her career, for whichshe was awarded a Nobel prize in 1983.
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Neutralism
z The neutral theory of molecular evolutionwas introduced by Motoo Kimura in the late1960s and early 1970s. The theory statesthat the vast majority of evolutionary changesat the molecular level are caused by randomdrift of selectively neutral mutants.
Neutralism
z Many genes never used (cant be subject toselection)
z Both genes and mutations (selectivelyneutral) can accumulate for large changes
z Pleiotropy Genes that code for multiple
features- some features carried along
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Types of Strange Genes
z Quantitative Inheritance
Eg. Weight/height depends on several Genes
AABBCCDD-biggest
aabbccdd- smallest
AAbbCCdd in between
Types of Strange Genes
z Structural genes and regulatory genes-regulatory genes control many structuralgenes so change in reg. means manychanges in structure.
z Junk genes dont seem to do anything
z Homeotic genes make major changes limb in wrong place
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Macroevolution
z Robert Goldschmidt
Structural and regulatory genes
Macroevolution and the hopeful monster- theproblem of a mate
Breakthroughs in embryology change can takeplace in several individuals
Evolution and Paleontology
z G. G. Simpson gradualism in the fossilrecord
z Biostratigraphy Practitioners used stasis inthe fossil record
z
Eldrich and Gould Species are inflexibleand non-responsive to the environment
z Sewall Wright Species are a heirarchicallevel above individuals and populations.
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Evolution and Paleontology
z Species Sorting
Does natural selection work on species?
Competition is between species (not individuals?)
Extinction
Species speciate, not organisms
A new theory of evolution
z Macroevolution
z Allopatric Speciation
z Punctuated Equilibrium
z Species sorting
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Answers to the isms
z Reductionism neither the individual nor thespecies is merely the sum of its genes
z Panselectionism some changes are neutralto selection; many of such changes are pre-adaptive
Answers to isms
z Extrapolationism small changes do not addup. Small changes are irrelevant; speciationrequires large changes
z Gradualism Species are static. They do
not change gradually. New species appear
fully formed, abruptly.