Evolution by fdshsdhs



Chapters 22 - 26
Processes by which living organisms originated on
Earth and have been diversified and modified
through sustained changes in form and function.
The earliest known fossil organisms are single-
celled forms resembling modern bacteria (3.4 bya)
Evolution has resulted in successive radiations of
new types of organisms, many which have become
extinct…and some which are present day flora and
fauna…extinction & diversification continue
      Origin of Life on Earth
Steps Proposed in the Origin of Life
  Formation of the Earth ~4.6 bya and its acquisition of volatile
  organic chemicals by collision with comets and meteorites
  (precursors of biochemical molecules)
  Prebiotic synthesis and accumulation of amino acids, purines,
  pyrimidines, sugars, lipids and other organic molecules in the
  primitive terrestrial environment
  Prebiotic condensation reactions involving synthesis of polymers
  of peptides (proteins), and nucleic acids (RNA/ ribozymes) with
  self-replicating and catalytic abilities
        Origins continued…
Steps Proposed in the Origin of Life
  Synthesis of lipids, their self-assembly into double-
  layered membranes and liposomes, and the “capturing”
  of prebiotic (self-replicating and catalytic) molecules
  within their boundaries
  Formation of a protobiont; this is an immediate
  precursor to the first living systems. Such protobionts
  would exhibit cooperative interactions between small
  catalytic peptides, replicative molecules, proto-tRNA,
  and protoribosomes. Ex., Liposome
  RNA (PNA, more stable early form) arose before DNA
Scenarios to the Origin of Life
Ocean Surface (Tidal
Pools) – This popular
hypothesis suggests life
arose in a tidepool, pond
or on moist clay on the
primeval Earth. Gases
from volcanoes would
have been energised by
UV light or electrical
discharges to form the
prebiotic molecules in
froth (Miller-Urey Expt)
Scenarios for the Origin of Life
Panspermia – Cosmic ancestry is a serious
scientific hypothesis that proposes living
organisms were “seeded” on Earth as passengers
aboard comets and meteors. Such incoming
organisms would have to survive the heat of re-
20080326.html Probe Finds Organic soup on Saturn Moon (Enceladus)
  Scenarios for Origin of Life
Undersea Thermal Vents
– A recently proposed
hypothesis suggests that
life may have arisen at
ancient volcanic vents
(called smokers). This
environment provides the
necessary gases, energy,
and a possible source of
catalysts (metal sulfides).
   Origin of Eukaryotic Cells
(know the endosymbiotic theory)
Geologic (3D)
         Geologic Time (video)
Life originated 3.4 bya Early Earth Environment lacked free oxygen (Urey-
Miller Experiment)  concentrations of molecules led to synthesis of active
chemical groupings of molecules and interactions of chemical compounds 
rudimentary genetic system  Natural Selection  Anaerobic Prokaryotes
(bacteria) Blue-Green Algae and aerobic photosynthesis Amalgamation
of distinct cell types (first eukaryotes; endosymbiotic theory) blue-green
algae evolved into chloroplasts & aerobic bacteria evolved into mitochodria
DNA may have arisen through prokaryotic symbionts  single-celled
eukaryotes developed complex modes of living and advanced types of
reproduction multicellular plants and animals w/ free oxygen and food
supplies abundant (700 mya) basic body plans of modern animals developed
with a remarkable burst of evolutionary diversity (700 – 570 mya)  jellyfish
and burrowing worm skeletons (570 mya)fishland plants (400
mya)arthropods (some evolving into insects) (360 mya)Dinosaurs and
mammals (135 mya)extinction of dinosaurs (65 mya)human evolution (2
mya) *Know general steps (See pbs evolution web site!)
Landmarks in the Origin of Life
4.6 bya Formation of the Earth and acquisition of volatile organic chemicals
4.0 bya protobiont
3.5 bya oldest microbial community now known is from Apex chert of northwestern
Australia (cyanobacteria fossils and stromatolites)
2.7 bya Compounds of oily residue squeezed out of Australian Shale suggests presence
of eukaryotic cells (1 by before original prediction)
2.5 bya Molecular fossil of cyanobacteria, 2-methylhopane, is abundant in organic rich
sedimentary rocks from the Mount McRae shale in western Australia
2.1 bya fossil imprints appear in the geological record that are so large they can only be
eukaryotic cells
1.1 bya Grooves in sandstone fron the Vindhyan Basin (central India) may be burrows
of ancient worm-like creatures (500 my before other previous evidence)
0.55 bya fossils of more complex, multi-celled creatures (e.g., fossils 1 meter across
have been found in Ediacara Hilles, Finders Ranges, South Australia)
To present Fossil history of large eukaryotic organisms is well documented
Do Activity on PBS Evolution Website- Deep Time
Extra Credit: Go to Ocean Journey, Prehistoric Journey and/or new A&P exhibit
or Ecology extra credit, DMNS
Evidence for Evolution (See Word table)
 Paleontology (fossil record)
 Comparative anatomy
 Vestigial Structures
 Comparative Embryology (developmental stages)
 Comparative Physiology (similar enzymes, hormones, etc…)
 Taxonomy (classification…see overhead schemas)
 Biogeography (isolation mechanisms)
 Genetics (gene mutations, chromosomal rearrangements, chromosome
 segment doubling produce variations)
 DNA, RNA, Protein comparative analysis
 Artificial Selection (See “Dog Evolution” video)
 See: http://www.pbs.org/wgbh/evolution/
 See: Campbell Powerpoint 22-09 to 22-15
 Video Clips: Evidence for Theory of Evolution and Agents of
           Fossil Formation
Fossils are remains of long-dead organisms that have
escaped decay and have, after many years, become part of
the Earth’s crust.
Preserved remains such as an impression (cast), or marks
made during lifetime (trace fossils)
Rapid burial of the organism usually in water-borne
sediment where minerals are added and removed
Provide a record of the appearance and extinction of
organisms; calibrated against a time scale (dating
techniques-relative v. radiometric)…build a picture of
evolutionary changes over time.
                   Fossil Formation
Modes of Preservation
    Silification- silica weathered volcanic ash is gradually
    incorporated into partly decayed wool (petrification)
    Phosphatisation- bones and teeth are preserved phosphate
    Pyritisation- Iron pyrite replaces hard remains of the dead
    Tar pit- animals fall into and are trapped in a mixture of tar and
    Trapped in Amber- gum from conifers traps insects and then
    Limestone- Calcium carbonate from the remains of marine
    plankton is deposited as a sediment that traps te remains of sea
    Show fossils!
Transitional Fossils- a mixture of traits that are found
in 2 different, but related, taxonomic groups (e.g., Archaeopteryx)

            Walking with the Dinosaurs: Genetics Video
                  Dating Fossils
Fossils are rarely dated directly; the rocks in which they are found are
Methods using Radioisotopes: Fission Track (U-235); Radiocarbon
(C-14); Potassium/Argon (volcanic rocks above or below fossil
strata); Uranium series (U-235, U-238) into thorium (th230) and U-
Non-Isotopic methods: Palaeomagnetism (alignment of Earth’s
magnetic field at the same time rock sample was last heated above
critical level); Thermoluminescence (measures the light emitted by a
sample of quartz and/or zircon grains); Electron Spin Resonance
(measures microwave energy absorbed by samples); Amino Acid
Racemisation (measures the gradual conversion of Left to right
handed aas); Varve (measures the distinct, annual deposits of
sediments in lakes); Tree-ring (measures annual growth rings of trees
and can be cross-referenced with C-140; Relative (position in rock
Trilobites that lived in the seas
hundreds of millions of years ago…
Historical Background
         Early Evolutionary Studies
          (see more notes on-line)
Erasmus Darwin (1731-1802): Evolution of “inheritance of acquired characteristics”
Georges Cuvier ( 1769-1832): catastrophic extinctions explained unique sets of fossil species
between successive strata
James Hutton (1726-1797): theory of Gradualism, profound change is the cumulative product of
slow but continuous processes
Reverand Thomas Malthus (1766-1834): “An Essay on the Principles of Population” attempted to
justify the squalid conditions of the poor by stating that poverty and starvation were merely a
consequence of overpopulation
Charles Lyell (1797-1875): “Principles of Geology” proposed that the geological processes we
observe today have always been occurring and the Earth is therefore very old
Hebert Spencer (1820-1903): proposed “survival of the fittest”
Alfred Wallace (1823-1913): “Theory of Natural Selection”
Gregor Mendel (1822-1884) model of inheritance
August Weisman (1834-1914) chromosomes as the basis of heredity (demolishes acquired
R.A. Fischer (1890-1962), J.B.S. Haldane (1898-1964), Sewall Wright (1889-1988) Founding of
population genetics and mathematical aspects of evolution and genetics
Julian Huxley (1887-1975), Ernst Mayer (1904-2005), T. Dobzhansky (1900-1975) helped form
the mordern or synthetic theory of Darwinian Evolution incorporating developments in genetics,
palaeontology, and other brances of biology
     Early Evolutionary Studies
No scientific explanations of evolution
were given until the 18th Century
The growth of natural history led to
increased knowledge of fossils & living
Jean Baptiste Lamarck (1744-
1829): “Philosophe Zoologique”:
patterns of resemblance found in
various creatures arose through
evolutionary modifications of a
common lineage…environmental
changes evoke in individual
animals direct adaptive responses
that are passed on as inheritable
traits (ex. Giraffe’s long neck); idea
of use and disuse and inheritance of
acquired characteristics
May have some merit with
epigenome and immune system
Early Evolutionary Studies
               Charles Darwin (1859) published
               his theory…offspring inherit a
               resemblance to their parents not
               solely due to environment…in
               nature individual’s with traits that
               made them better adjusted to their
               environments or gave them higher
               reproductive capacities…”higher
               Tenets: 1) more individuals are
               born than survive; 2) when
               environmental changes occur,
               populations require new properties
               to maintain their fitness; 3) traits
               are inheritable; 4) either adaptation
               or extinction occurs
               Alfred Wallace had the same ideas!
What was Darwin like?
What can we learn from the Galapagos
Islands and how does it relate to
Natural Selection? Video Clip
Darwin’s Discoveries Video Clip
    Early Evolutionary Studies
Mendel discovered that
characteristics are transmitted
across generations in discrete
units, now known as “genes,” in
a predictable manner
Inheritable changes can occur
without regard to
environment…evolution is
driven onward by the random
accumulation of favorable
mutational changes
Early Evolutionary Studies
               Hugo de Vries, Thomas
               Morgan, & William Bateson :
               natural selection, evolution
               directed by adaptive fitness,
               minor role (“mutationists”)
    Early Evolutionary Studies
Sewall Wright & J.B.S.
Haldane, population geneticists,
and several others
independently developed
arguments that when a mutation
is immediately favored, its
spread within a population
depends on: 1) size of
population; 2) length of
generations; 3) degree to which
mutation is favorable; 4) rate at
which the same mutation
reappears in the descendants
Early Evolutionary Studies Conclusions
 A gene is favorable only under certain environmental conditions
 The total number of genes available for the next generation can be
 large: genetic variability & the gene pool
 Sexual reproduction ensures that the genes are rearranged in each
 generation: recombination
 When a population is stable, the gene frequency remains the same
 (even though the genes in individuals may be recombined in different
 When the gene frequencies in the pool change in a sustained manner,
 evolution is occurring!
 Mutations provide the gene pool with a continuous supply of new
 genes; through natural selection, gene frequencies change so that
 advantageous genes occur in greater proportions
What is considered to be an
 “advantageous” gene?
Are all acquired traits good, bad, or
     somewhere in-between?
Early Evolutionary Studies
               Mathematical support
               by Hardy and
               Weinberg (1908)
               (p + q)2 = p2 + 2pq +
               q2 = 1, where p =
               allelic freq. of A and
               and q = allelic freq. of
               a in a population
               Conforms to a Punnet
  Hardy – Weinberg Theorem
The frequency of alleles in a population will remain the
same regardless of the starting frequencies (“equilibrium”)
if: 1) population is large; 2) matings are random; 3) there
are no net changes in gene pool due to mutation; 4) there is
no migration of individuals into and out of the population;
5) there is no selection…all genotypes are equal in
reproductive success
Hence, evolution does occur if one of the above is
See Population Genetics Lab: H-W Theorem
“Nothing in biology makes sense except
in the light of evolution…”
 Theodosius Dobzhansky in the
 “Genetics and Origin of
 Species,” extended the
 mathematical arguments with
 experimental and observational
 Demonstrated adaptive genetic
 changes in large populations of
 fruit flies as a result of
 controlled environmental
 changes…compatible with
 Darwinian natural selection
Modern Synthesis or Synthetic
                Ernst Mayer (zoologist) showed that
                new species usually arise in geographic
                isolation often following a genetic
                “revolution” that rapidly changes the
                gene pool
                George Simpson (paleontologist)
                showed from the fossil record that rates
                and modes of evolution are correlated
                G. Ledyard Stebbins (botanist) showed
                that plants display evolutionary patterns
                similar to those of animals
                The Modern Synthesis or Synthetic
                Theory is strongly supported by
                observation and experiment!
   Modern Synthesis or Synthetic
James Watson, Francis Crick, and
Rosalind Franklin demonstrated
that DNA is the genetic molecule
of inheritance
Mutations are known to be changes
in the position of a gene, or the
information coded in a gene, that
can affect the function of the
protein for which the gene is
Natural Selection can then operate
to favor or suppress a particular
gene according to how strongly its
protein product contributes to the
reproductive success of the
Punctuated Equilibrium
             Stephen Jay Gould and Niles
             Eldredge: Theory of Punctuated
             Equilibrium (1972)…species
             undergo most of their
             morphological modification as
             they first separate from the
             parent species showing little
             change as they produce
             additional species…gradual
             change is replaced with stasis
             punctuated with episodes of
             speciation (See additional
       Mechanism of Evolution
Peppered moth example: light v. dark variants; frequency changes due to
environmental conditions
Mechanisms of: 1) Geographic Isolation (Darwin’s Galapagos Finches &
Hawaiian Fruit Flies); 2) Genetic Drift (gene freq. Change by the chance
failure of progeny to reproduce to the exact gene proportions of their
parents…natural disaster); 3) Founder effect (migration of individuals to an
isolated population); 4) Mutations (seems to be the chief agent); 5) Gene
Flow (change in gene pools due to migration of individuals between
populations); 6) Nonrandom matings (inbreeding, mate selection); 7)
Natural Selection via differential reproductive success (increases freq. Of
some alleles and diminishes others)
                   Paths of Speciation
Speciation- microevolution is changes to a single gene pool; macroevolution is changes
above the species level (feather appearance)
Anagenesis-phyletic evolution- accumulation of changes that gradually transform a given
species into a species with different characteristics
Cladogenesis-branching evolution- is the splitting of a gene pool into two or more
separate pools, which give rise to one or more new species
Allopatric- gene flow is interupted when a population is divided into geographically
isolated subpopulations (ex., squirrels in Grand Canyon); “Other country”
Sympatric- a small population becomes a new species without geographic isolation;
polyploidy or autoploidy (more than 2 sets of chromosomes due to failure to complete cell
division); “Same country”
Hybridization- mating or crossing of 2 true-breeding varieties
Adaptive radiation- evolution of many diversely adapted species from a common ancestor
upon introduction to various new environmental opportunities and challenges
              Results of Evolution
Speciation: anagenesis v. cladogenesis (See Speciation
Allopatric Speciation: a process thought to have been responsible for a great many
species formation; when an ancestral population becomes segregated by a geographic
barrier or is divided into 2 populations geographically (Geographical fragmentation
important- 1) moving to new environments, 2) geographical isolation, 3) different
selection pressures, 4) reproductive isolation)
Sympatric Speciation: new species may be formed even where there is no separation of
the gene pools by physical barriers, but separation due to radical change in the genome-
1)speciation through niche differentiation, either niche isolation or reproductive
isolation; 2) speciation by polyploidy or allopolyploidy (doubling of chromosomes)
Reproductive barriers separate species (prezygotic, habitats, behavioral, temporal,
mechanical, gametic, reduced hybrid viability, reduced hybrid fertility, hybrid
breakdown, & introgression); see p.474-475
See bio.kimunity Ppts. 1 and 2
Pathways of Evolution…Not Goal
Divergent evolution (diversification of an ancestral group into 2 or more species in
different habitats)
Covergent evolution (common selection pressures bring about similar adaptations;
analogous structures)
Coevolution (describes cases where two or more species reciprocally affect each other’s
Adaptive radiation (diversification both structural and ecological among descendants
of a single ancestral group to occupy different niches)
Parallel evolution
Macroevolution- changes can accumulation through many speciation events such as
changes in rate and timing and spatial patterns; allometric= different growth rates for
different parts of the body determine body proportions; paedomorphosis= sexually
mature form of species retains features that were juvenile structures in an ancestral
species; ex., growth rates of humans, comparison of chimp and human skulls, ground v.
tree- dwelling salamanders; axolotl; Hox genes and evolution of tetrapod limbs; Hox
mutations and the origin of vertebrates
Pictures and graphics from google.com
Information supplemented by: Campbell, et
al Biology, Encarta, and Professor
Farabee’s web site and explorebiology.com

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