The Origin and Evolution of Life by Z0Kgs0P

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									The Origin and Evolution of
            Life
                      The Nature of Life
• Life
  – During last 4 by adapted to many environments and
    physico-chemical conditions
  – Most organisms live at 1 atm and 0-40oC; Some
    Bacteria can live up to 1400 atm or -18 to 104oC
  – Unicellular Organisms vs Non Living Molecules
    (Amino acids, RNA (ribonucleic acid)
     •   reproduction
     •   growth via nutrients and energy
     •   responds to outside stimuli
     •   Share same genetic code
     •   chemical uniformity
          – C, O, H, N, P >> nucleic acids, proteins, carbohydrates, fats
             The Nature of Life
• Prokaryote vs. Eukaryote
  – small (1-10 um) vs large (10-100um)
  – No nucleus vs Nucleus
  – DNA in nucleoid vs Membrane bounded
    nucleus containing chromosomes made of
    DNA, RNA
  – Cell division direct (binary fission) vs mitosis
    and miosis
  – Rare multicellular forms vs Multicellular
    organism with extensive development of tissues
     Building Blocks: Pattern shared by all life
• All Life: DNA => RNA => Protein
• DNA architect plans for building (instructions to build
  proteins in the ribosome) transcribes information into
  RNA (Blueprint)
• RNA messenger translates blueprint into proteins in
  the ribosomes
• Genes code for specific proteins (enzymes)
• Enzymes are proteins that control all chemical
  reactions
• Order of nitrogenous bases (read in groups of 3) {A,
  T, C, G} determines the type of proteins made
• Each group of 3 codes for a specific amino acid
                        DNA: Our Genetic
                             Code
Spiral double helix of sugars and
phosphate linked together by
nitrogenous bases such as Thymine,
Cytosine, Adenine and Guanine.

A Gene is a portion of the DNA
molecule that includes approximately
1500 base pairs and a Chromosome
contains many genes
    The Origin of Life
• 19th Century Ideas
  – life created supernaturally
     • cannot be proven scientifically
  – continually being formed by
    spontaneous generation of nonliving
    matter
     • untenable by numerous experiments
• 20th Century
  – life generated spontaneously and
    evolved through different steps
                   The Origin of Life
• Origin of life is NOT an event
• Origin of life is a continuous process
• Stages
   – inorganic production of key simple organic molecules
   – production of more complex molecules that can synthesize
     more of the same molecule
   – development of a genetic code of self-replicating molecules
     (RNA,DNA,proteins)
   – production of the first cell by separation of these codes
     from the outer world by a membrane
• Ocean environment by 4.0 by- fossils evident at
  3.8by
         The Origin of Life
• Many complex organic molecules must
  have formed before an organism produced
• The process of life took many steps over
  the first 600 my
• Probability theory would dictate that at
  least one random event would have
  produced a result
• This process cannot occur on Earth today
  because the simple organism would be
  destroyed by oxidation or predation
      Steps in the Origin of Life
• Aerobic vs. Anaerobic
  – oxygen poisons living cells so early life was
    anaerobic
• Lack of free Oxygen >> No Ozone layer
  – UV radiation kills cells so life had to originate at
    depth
  – Water depths of 10m or more
• Models
  – non-oxidizing secondary atmosphere rich in the
    constituent chemicals for life--H2O, CO2, N
  – Energy in the form of UV radiation & Hot springs
            Steps in Origin of Life
• Before the first cell>>Chemical Evolution
  – production of significant molecules necessary for life
• Phosphoric acid crucial to cell chemistry>> phosphoric
  acid can bond molecules and promote long chain
  molecule formation
• Amino acids formed first since they do not form if
  oxygen present
  – probably formed on clay surfaces since they are attractive
    and absorptive, also protection from UV
• Larger Molecules
  – amino acids are linked together by dehydration synthesis
    (water loss), clays have potential to absorb water, thus
    amino acids could be linked on clay surfaces
             Experimental Studies
• A. I. Oparin- 1930s
  – Produced sugars and fatty acids from the constituents of
    an early atmosphere
• Urey and Miller- 1953
  – Production of cyanide, formaldehyde and 4 different amino
    acids from water vapor, methane, hydrogen and ammonia
    and electrical sparks
• Subsequent Experiments
  – Production of 18 of the 20 known amino acids and
    extremely simple forms of DNA from gases rich in water
    vapor, CO2, and nitrogen and UV radiation
  – S.W. Fox (1959) produced protein-like (protenoids) chains
    from a mixture of 18 amino acids at 70oC in the presence
    of phosphoric acid
     The Environment for Life
• Volcanic Hot Springs
• Oceanic hydrothermal
  vent system
• Deep (below the level
  of UV penetration)
• Clays and/or Zeolites
  as templates
• Similarity with present
  day chemosynthetic
  heterotrophic
  organisms
              The First Cells
• All cells use the same genetic code
• Archaeobacteria- most primitive
  – Heterotrophs: obtain energy from surroundings by
    some chemical reaction
  – Obtain energy by converting CO2 and H2 to CH4 or by
    the reduction of sulfur compounds
• Eubacteria
  – 10 Phyla, including cyanobacteria (Autotrophs:
    manufacture their own food source)
• First Cells poorly developed metabolic
  systems
  – absorbed nutrients directly
  – fermentation
                        Life
• Prokaryota
  –   Appear 3.8-3.6 by
  –   no nucleus
  –   single loop chromosome with all genes
  –   reproduction-binary fission
• Eukaryota
  – Single cell appear 2 by
  – Multicellular appear as trace fossils 1by and as body
    fossils 700my
  – Nucleus with 2 pairs of chromosomes (2 copies of all
    genes)
  – Asexual and SEXUAL reproduction>> more
    combinations
Endosymbiotic Theory- Evidence the
 observation that mitochondria and chloroplasts
      posses their own genetic apparatus
• Stromatolites:
  laminated structures
  composed of layers
  of cyanobacterial
  (Prokaryotic
  photosynthetic
  bacteria) filaments
  and sediment
• Foraminifera:
  Calcium carbonate
  secreting unicellular
  eukaryotic organisms,
  planktonic and
  marine
                       Taxonomic Hierarchy
• Linnean Classification
  –   Kingdom
  –   Phylum (Phyla)
  –   Class
  –   Order
  –   Suborder
  –   Superfamily
  –   Family
  –   Genus (genera)
  –   Species
• Example
  – Animalia, Chordata,
    Mammalia, Primate,
    Anthropoidea, Hominoidea,
    Hominidae, Homo sapiens
           Organic Evolution
• Challenge to special creation in the 18th
  century
• Buffon
  – Environment involved
  – Concept of species
• Lamarck
  – “inner want”
     • Inherited characteristics
     • Little used structures dissappear
               How Evolution Works
• Organic Evolution is the change in populations
  of species with time
  –   between species
  –   within a species
  –   during the lifetime of an individual
  –   at the chromosomal level
  –   at the molecular DNA level
• Species produce more offspring than can survive to
  maturity
• Individual species have different genetic combinations,
  thus also different anatomical attributes
• Some individuals better suited to their environments
         How Evolution Works
• Organic Variation and Heredity
  – individuals look like their parents but are not
    exactly like them
  – sexual reproduction design to produce many
    and varied combinations
  – random mutations in gene replication 1 in
    10,000
  – mutations due to chemical reactions and
    radiation
• Reproductive Potential
• Natural Selection
(A) mitosis, (B)
meiosis, and (C)
  fertilization.
       How Evolution Works
• Reproductive Potential
  – potential for rapid expansion of a species in a
    given geographical area
  – a species will fill a niche until it reaches a
    climax
• Natural Selection (Darwin)
  – interaction between genetics and environment
  – “survival of the fittest” (H. Spencer)
  – certain individuals are better suited
    (engineered) for the habitat they inhabit
Physical Factors Controlling Natural
             Selection
•   Temperature (land and sea)
•   Water Depth (sea)
•   Altitude (land)
•   Rainfall (land)
•   Humidity (land)
•   Salinity (sea)
•   Light Intensity (land and sea)
•   Substrate (sea and land)
•   Seasonality (land)
•   Tidal Range (sea)
      Biological Factors: The Trophic
•
                       Relationship
    Food web sets limits on
  the number of species
• Elements govern the
  structure
    –   predation
    –   parasitism
    –   competition
    –   symbiosis
• Pyramid structure
   – each trophic level
     must have a lower
     biomass than the
     level below it (as
     much as 90% drop)
           Modes of Evolution
•   Transformation
•   Speciation
•   Extinction
•   Adaptive Radiation
•   Divergent, Parallel and Convergent
    Evolution
  Modes of Evolution: Transformation
• Gradualism (Darwinian
  concept)
• Change of properties
  (morphological) so that over
  time it warrants to be called
  something else
• Transitional forms
• This mode occurs in
  species with a relatively
  small breeding population
• Common in vertebrates of
  small isolated populations
  that are broad ranging
• Adaptations to changing
  environments
   Gradualism
• Evolution of the Horse
• Fossils preserved in
  consecutive formations
  exhibit sequential
  morphologic changes
• Paleocene: small browsing
  animal the size of a dog,
  with 4 toes on the front feet
  and 3 on the back, low
  crown and weak enamel on
  teeth (woodland-leaves)
• In progressively younger
  rocks the fossils exhibit
  larger size, reduction of side
  toes, increase in height and
  complexity of teeth
  (grasslands-grasses w/ silt)
Fig. 3.15a
   An example of
    progressive
    evolutionary
 change in a group
     of Permian
     ammonoid
   cephalopods.
 (From Spinosa,C. Furnish, W.
M., and Glenister, B. F. 1975. J.
   Paleontol. 49(2): 239-283.)
   Modes of Evolution: Punctuated
             Equilibria
• 2 species A-B, and C
• A is a widespread species
  evolving slowly or not at all
• B is an isolated small part
  of species A with a deviant
  anatomy
• After extinction event, B is
  the only survivor and it
  spreads out over a larger
  area
• Unless the small population
  B is found, then A appears
  to change abruptly into C
Modes of Evolution: Punctuated
   Equilibria vs Gradualism
• Morphological change occurs
  in a sideward direction
• Time is depicted in a vertical
  direction
• The short horizontal side
  brances of the punctualistic
  model depict sudden change,
  whereas the inclined
  branches of the gradualistic
  model suggest slow uniform
  change through time
 Modes of Evolution: Speciation
• The splitting of a
  species into two
  or more parts as
  the result of some
  ecological or
  geographic barrier
  or due to
  migration
• Barriers can be
  canyons,
  mountain ranges,
  isthmus, deserts,
  ocean basin
                      Speciation
• Intercontinental
  migrations of
  members of the
  camel family
• Camels originate
  in North America
  during the
  Eocene
• Migration through
  land bridges
• Geographic and
  ecological
  barriers
              EXTINCTION
• The rapid disappearance of a group of
  organisms
• As a response to an ecological catastrophe
  – Climatic Change
• The extinction of one group releases the
  resources for another group to thrive
• Background Rate as a result of random factors:
  – competition, predation, changes in temp., changes in
    salinity
• Mass extinctions >> Catastrophic
  – asteroid collision, rapid oceanic turn-over;
    accelerated rates of plate tectonic (volcanism)
               Adaptive Radiation
• Organisms rapidly filling new ecological niches
  increasing both numbers and diversity
• Typically lasts from 5 to 10 my
• Major expansion in adaptation of one or more
  original minor taxa
• Steps
  –   extinction rate drops
  –   competition is reduced
  –   speciation occurs
  –   species transforms rapidly into different descendants
• Creation of new ecological niches by plate tectonics
         Divergent Evolution: Homologous
                    Structures
• In 4-limbed vertebrates, the
  bones of the limbs may vary
  in size and shape but they
  are fundamentally similar and
  in similar relative positions
• Basically similar structures in
  dissimilar organisms are
  referred to as homologous
• The differences in
  homologous structures are
  the result of variations and
  adaptations to particular
  environmental conditions,         c:carpal; h:humerous;
  similarities >>common             m:metacarpal; r:radius;
  ancestry                          u:ulna; 1-5:digits
              Parallel Evolution
• Two related species that evolve
  similar specializations to the same
  sort of habitat but independently
• a) Thoatherium, a Miocene
  litoptern
• b) Equus, a modern horse
• Both shared a common 5 toed
  hoof mammal ancestor and
  independently evolved to a one-
  toed foot for maximum running
  endurance
           Convergent Evolution
• Represented by animals with
  different ancestry evolving to
  similar forms and functions in
  different places or at different times
• a) Dinogorgon, a saber-toothed
  therapsid from the Permian of S.
  America
• b) Thylacosmilus, a saber-toothed
  marsupial from the Miocene of
  Argentina
• c) Smilodon, a saber-toothed cat
  from the Pleistocene of N. America
• The historical development of
                                    Phylogeny
  groups of organisms so as to
  depict descent from ancestors
• The depiction is called a
  phylogenetic tree
• Branches on the tree are called
  clades
• In cladistic phylogeny
  organisms are analyzed on the
  basis of characteristics they
  share in order to determine
  their ancestor-descendent          Simple cladogram
  relationship                       showing the simple
• The shorter the links between      primitive trait of a
  groups the closer the              vertebral column
  relationship
          Evolutionary “Laws”
•   Haeckel’s Law
•   Dollo’s Law
•   Cope’s Law
•   Williston’s Law
Haeckel’s Law: Ontogeny Recapitulates Phylogeny
In its development
from embryo to
adult, the individual
passes through
(recapitulates) the
evolutionary stages
of its ancestors. Thus
the human embryo
progresses from a
single cell thru
higher invertebrate
stages to resembling
a fish, a reptile and
finally a mammal
              Dollo’s Law
• Structures once lost cannot be regained
• Difficulty in duplicating the genetic
  mechanism of the development of a
  structure
                      Cope’s Law
• Organisms generally increase
  in size from their ancestors
• This is possibly due to
   – larger organisms have fewer
     predators and a larger size
     protects against many smaller
     predators
   – food utilization is more efficient
   – thermal inertia increases, constant
     body temperature
• Increase in size >> decrease in
  population >> decrease in
  biomass
• Leads to extinction and
  increases opportunity for others
             Williston’s Law
• Common
  evolutionary trends
  occur in related
  organisms with
  serially homologous
  structures
• Thus structures are
  reduced in numbers
• Structures become
  more differentiated

								
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