Biological Evolution: Observation vs' Mechanism

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Biological Evolution Observation vs. Mechanism

• Definition a change in the inheritable
  composition of a biological population over time
  (time generations)
• Observable in Present
• Antibiotic resistance
• http//evolution.berkeley.edu/evosite/relevance/IA
  1antibiotics.shtml
• Pesticide resistance
• http//www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd
  RetrievedbPubMedlist_uids2212232doptAbstract
  
• Elephants being born without tusks
• http//www.elefantasia.com/modules/news/article.ph
  p?storyid71
• http//www.bbcwildlifemagazine.com/newsread.asp?id
  12842scrollCount2

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Thus, biological evolution in historical times is
an OBSERVATION
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Tuskless Elephanthttp//www.wildlife-pictures-onl
ine.com/image-files/xepkp5.jpg
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What About Prehistory?

• Is biological evolution responsible for the
  existence and variety of all life?
• Mutation (random) and natural selection
  (non-random) proposed as primary mechanism for
  evolution

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Hypothesis what are the implications?

• Inefficiency
• Lack of perfect adaptations
• Extreme genetic similarities due common descent
• Is there evidence to support these implications?

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YES - Five main categories of evidence

• Fossils - evidence for extinction(http//www.talko
  rigins.org/faqs/homs/specimen.htmlrobustus)
• http//www.toyen.uio.no/palmus/galleri/montre/engl
  ish/highlights/01.htm
• Biogeography - biological distributions
  reflecting barriers and geological
  transitions(http//www.amnh.org/exhibitions/expedi
  tions/treasure_fossil/Treasures/Tasmanian_Wolf/tas
  mania.html?acts)
• http//www.nearctica.com/ecology/habitats/biogeo.h
  tm

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Additional Factors

• Ontogeny - existence of physiological and
  anatomical characteristics which appear ancestral
  http//www.skepticreport.com/creationism/vestigial
  .htm
• Vestigial organs and behavior
• Whale hips
• Snake legs
• Goose pimples in humans http//www.livescience.com
  /animalworld/top10_vestigial_organs-9.html

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DNA Homologieshttp//www.mydna.com/genes/genetics
/genetics101/primer_phylogenetics.html
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Imperfections/maladaptations demonstrates
biological evolution has been working throughout
Earths existence
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Story of Biological Evolution

• Early evolution
• Survival of fittest is a subset of survival of
  the stable
• More stable things last longer than unstable
• Stability through duplication

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Stability Through Duplication

• Example Word Processing Document
• One copy and loose power - very unstable
• Two copies (one saved on hard drive) - more
  stable
• Several copies saved on floppies - yet more
  stable

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Note that each individual copy is no more stable
than any other - the increase is in the
document's (information content) stability
because of the existence of multiple copies
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First genes simply molecules with capacity for
self-replication - so-called replicators - leads
to stability through copies
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Early Problems

• Duplication not perfect
• Errors lead to new replicators
• Soon many different replicators
• Question which are more stable?

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Three Essential Characteristics

• Longevity of individual molecules
• Fidelity/accuracy of duplication
• Fecundity/speed of duplication

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Problem 2 - Limited Resources

• What happened when all replicator building blocks
  were used up?
• Two choices
• Stop replicating become unstable
• Find new source of building materials

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Primary source - other replicators
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Results

• Any replicator which could use building blocks
  from another automatically more stable
• Chemical carnivores evolve
• New problem - how do prey replicators respond?

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Stability also linked now to resistance to
chemical attack

• Replicators which protect themselves (i.e.,
  surround themselves with a protein coat) more
  stable than those who could not
• Next step - carnivores capable of eating through
  the protein coat

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Co-Evolutionary Arms Race

• Competition for limited resources fuels
  evolutionary change

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Recall Basic Mechanism

• Source of new types of replicators - copy errors
  (now called mutations)
• Stability of different types of replicators
  linked to numbers of copies produced
• Basic characteristics - longevity, fidelity,
  fecundity

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New Conditions

• Stability now linked to physical and social
  environment
• Type of protection needed depends on type of
  chemical attack
• Successful attack dependent on overcoming
  existing protection
• Called Co-Evolution

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Process of Informational Stability now called
Natural Selection
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Long-Term Results

• Replicators (now called genes) often live in
  colonies inside survival machines
• Survival of machine itself a secondary
  consideration
• Most important increase representation of genes
  (mostly through direct reproduction)

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Ultimate Purpose of All Life Survival of Genes
through Replication
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Critical Perspectives

• Natural selection selects among preexisting
  features
• Natural selection not 100 efficient
• Biological organisms history-dependent

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Selecting among Preexisting Features

• POW-made radio sets vs. engineered stereos
  evolution works only with what is available at
  the time- does not create best but rather best
  available
• Odd results might not match engineer's idea of
  how to accomplish task

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The Irish Elk (Megaloceros) Sexual Attraction
Gone Awry?

• Right Photo from http//sunset.ennis.ie/article.ph
  p3?id_article289
• Left Photo from http//www.ucmp.berkeley.edu/mamma
  l/artio/irishelk.html

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Efficiency Limitation

• Natural Selection not remove characteristics
  unless sufficiently harmful
• Vestigial organs/behaviors always possible, even
  likely

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Vestigial Legs in Some Snakeshttp//www.synapses.
co.uk/evolve/lec3i.html
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History-Dependence

• Analogy - computer program with IF...Then
  statement
• Ex. IF (I 10) THEN EXECUTE STATEMENT 10
• If I never 10, then statement 10 never executed
• Biological evolution leaves a lot of IF.. THEN..
  statements lying around

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Implications

• As environment changes, statements may lie
  dormant because conditions are not correct
• If conditions change, however, unexpected
  statements (i.e., physiological/behavioral
  responses) may be executed
• Genetic terms
• Penetrance
• Expressivity
• http//www.dogstuff.info/penetrance_kral.html

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Later Evolution

• Selection of genes within genomes (individuals
  live and die but genes go on and on)
• Team analogy
• You are a coach deciding on players from a pool
  of quarterbacks, defensive linemen, etc.
• Conditions
• Have no idea of initial talents of individuals
• Can only use team contests to select players for
  final roster

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Anyone Is Eligible to Try Out!http//www.umich.ed
u/bhl/stadium/stadtext/fbchi04.htm
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Procedure

• Create teams at random and have them play each
  other
• After each victory, player on that team gets a
  '' and after each loss, the player on the
  loosing side gets a '-
• As time goes on, better players show up more
  consistently on victorious teams, less capable on
  loosing teams

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Typical Results
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Consistency is the Critical Factor

• Good player occasionally on loosing team and bad
  player on winning team
• However, when players consistently on winning or
  loosing teams, that indicates the players are
  better or worse than their competitors

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Note that teams win or loose but individual
players are being selected (i.e., individual
animals live or die but particular genes are
being selected)
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Improve the Model

• Add Language as a Factor
• Consider situation if individual players spoke
  either French or German but not both
• Over time, teams would become all-French or
  all-German because of the importance of
  communication
• Even a good player, if he spoke only German,
  would have a difficult time if placed on the
  French team and vice versa

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In the final analysis, the frequency of genes in
succeeding generations is the only criteria for
evolutionary success
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Same is True In Biological Evolution

• Suppose there was a gene for sharp canines this
  might be selected for in a carnivore but selected
  against in a cow or horse
• The quality of a gene in terms of stability
  depends on its physical, social, and genetic
  environment

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Modeling Evolution

• Assume the following sentences represent
  perfect adaptations to a particular environment
• Target Adaptations
• THE CAT SWIMS WELL
• RED HATS WERE COOL
• BIG FAT SWANS HONK

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Beginning Sequence

• RHDGATSWPNCOELK

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One Possible Pathway

• RHDGATSWPNCOELK
• First Mutation
• RHDCATSWPNCOELK
• Next Retained
• THDCATSWPNCOELK

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• Next Retained
• THECATSWPNCOELK
• Next Retained
• THECATSWINCOELK
• Next Retained
• THECATSWIMCOELK

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• Next Retained
• THECATSWIMSOELK
• Next Retained
• THECATSWIMSWELK
• Next Retained
• THECATSWIMSWELL

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Final Product

• THE CAT SWIMS WELL

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Another Possible Pathway

• RHDGATSWPNCOELK
• First Mutation
• RHDHATSWPNCOELK
• Next Retained
• REDHATSWPNCOELK

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• Next Retained
• REDHATSWPNCOOLK
• Next Retained
• REDHATSWONCOOLK
• Next Retained
• REDHATSWONCOOLY

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Final Product

• RED HATS WON COOLY

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Another Possible Pathway

• RHDGATSWPTCOELK
• First Mutation
• RHDFATSWPTCOELK
• Next Retained
• RHDFATSWATCOELK

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• Next Retained
• RHDFATSWATSOELK
• Next Retained
• REDFATSWATSOELK
• Next Retained
• REDFATSWATSAELK

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Final Product

• RED FAT SWATS A ELK