Evolution Ch 7 Pt 1

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EvolutionCh 7Pt 1
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Wooly mammoth skeleton Mammoths lived 2 million
to about 9,000 years ago. They were about 9 to
15 feet tall. Where would scientists look for
possible reasons for extinction?
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5 mass extinctions1 underway

• Evidence of five major mass dying of life forms
  on Earth
• Each is followed by a succession of distinctly
  different organisms which can survive in the
  absence of predecessors
• Example dinosaurs died
• Gave way to rise of mammals
• Eventually humans appear

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Fossil succession shows
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Life, as we can best define it

• The definition must be built on descriptions
  that fit all living things.
• Living things are both complex and organized
• Living things grow and reproduce
• Living things respond to stimuli
• Living things acquire and use materials and
  energy
• Living things have (use) DNA to store information

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Misconceptions aboutevolution
?? Evolution proceeds strictly by chance ??
Evolved species must be more complex than the
predecessor ?? Where are the missing
links? ?? humans evolved from monkeys so monkeys
should no longer exist
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Theory of Evolution

• A theory explains a series of observations and
  often unifies related facts through supportive
  evidence.
• Evolution is based on the observed accumulated
  generation to generation changes within a defined
  group.
• Evolution accounts for
• similarities among life forms
• differences among life forms

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Jean-Baptiste de Lamarck

• (1744-1829) is best remembered for his theory of
  Inheritance of Acquired Characteristics
• -- new traits arise in organisms because of their
  needs and repetitive behaviors to meet those
  needs
• Acquired traits are somehow passed on to their
  descendants
• Lamarcks theory seemed logical at the time and
  was widely accepted

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Lamarks Theory
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Rethinkingwhy would giraffes develop or
actually express the trait of longer necks over
time?Was the acquired trait passed on?
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Darwin

• In 1859, Charles Robert Darwin (1809-1882)
  published
• On the Origin of Species
• In it he detailed his ideas on evolution
  formulated 20 years earlier
• he proposed a mechanism for evolution
• From 1831 to 1836, he had traveled along the
  southern continents and Europe.

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What most dont know about Charles Darwin

• Darwin born in England on Feb. 12, 1809 same
  day as Abraham Lincoln.
• Father a doctor. Mother affluent (Wedgwood
  pottery family) .
• Both families were free thinkers and
  philosophers.
• His private school education was useless for his
  interests his hobbies hunting, observing natural
  world, collecting things, and chemistry.

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About the same time..

• James Hutton was promoting his old earth and
  plutonic (igneous) rocks
• and Abraham Werner promoted Neptunism (all rocks
  precipitate from oceans).
• Darwin was exposed to Zoomania which promoted
  Lamarckian ideas. Learned taxidermy from a
  former black slave who inspired Darwin with his
  stories of the tropics.

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And a little more.

• Off to Cambridge, he studied to be a clergyman.
  Baptized into the Church of England, where it was
  compatible to be a naturalist.
• He hunted, caroused, and collected beetles.
• he learned to observe variations within a species
  from botanist and clergyman Professor Henslow.
• Studied geology with Adam Sedgwick, a
  catastrophism proponent who later named the
  Cambrian system of rocks in England.
• Learned to do field work and record observations
  meticulously.

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Darwin spent only 5 weeks in the
Galapagos Islands. Here he made observations
about distinct differences among similaranimals
that were directly related to foodsupply. He
published his ideas in 1859, 24 yrs. later.
Fig. 7-1, p. 115
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Observation of finchesin the Galapagos Islands
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What Darwin noticed

• Plant and animal breeders practice artificial
  selection
• breeding plants and animals with desirable traits
• A process of selection among variant types in
  nature could also bring about change
• Thomas Malthuss timely essay on population
  suggested that human competition for resources
  and high infant mortality limited a population
  size

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Natural Selection (Key Points)The mechanism

• Organisms in all populations posses heritable
  variations.
• size, speed, agility, visual acuity, digestive
  enzymes, color, and so forth
• Some variations are more favorable than others
• some have a competitive edge in acquiring
  resources and/or avoiding predators
• Not all young survive to reproductive maturity
• Those with favorable variations are more likely
  to survive and pass on their favorable variations

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Survival of the Fittest?

• Natural selection is sometimes expressed as
  survival of the fittest

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Survival of the Fittest What does it mean??

• Misconception
• among animals only the biggest, strongest, and
  fastest are likely to survive
• Maybe these traits are an advantage-- but natural
  selection may favor species other than the
  obviously bigger, stronger, or faster. Examples?
• Natural Selection involves differential rates of
  survival and reproductionSurvival of the species
  depends on producing offspring.

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Again, rethinking

• the smallest if resources are limited
• the most easily concealed
• those that adapt most readily to a new food
  source
• those having the ability to detoxify some
  substance
• Others?
• It helps to know what organisms had survived
  stressful conditions in the past .

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The peppered moth
Peppered moths had light colouration, which
effectively camouflaged them against the
light-coloured trees and lichens which they
rested upon
During the Industrial Revolution in England, many
of the lichens died out, and the trees that
peppered moths rested on became blackened by soot,
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So, is natural selection the mechanism for
evolution?

• Natural selection works on existing variations in
  a population
• It could not account for the origin of variations
• Critics reasoned that should a variant trait
  arise, it would blend with other traits and would
  be lost
• The answer to these criticisms existed even then
  in the work of Gregor Mendel, but remained
  obscure until 1900

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Gregor Mendel

• controlled genetic experiments with true-breeding
  strains of garden peas
• strains that when self-fertilized always display
  the same trait, such as flower color
• Traits are controlled by a pair of factors now
  called genes
• Genes occur in alternate forms, called alleles
• One allele may be dominant over another
• Offspring receive one allele of each pair from
  each parent

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Mendels Work

• The parental generation consisted of
  true-breeding strains
• RR red flowers
• rr white flowers
• Cross-fertilization yielded a second generation
• all with the Rr combination of alleles, in which
  the R (red) is dominant over r (white)

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Mendels Work

• The second generation, when self-fertilized
  produced a third generation with a ratio of three
  red-flowered plants to one white-flowered plant

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Why is this important?

• The factors (genes) controlling traits do not
  usually blend during inheritance
• Traits not expressed in each generation may not
  be lost even if not seen!
• Some variation in populations results from
  alternate expressions of genes (alleles)
• Variation can be maintained!
• Why is variation important to survival of a
  species?

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Modern Genetics
Complex, double-stranded helical molecules of
deoxyribonucleic acid (DNA) called chromosomes
are found in cells of all organisms Specific
segments of DNA are the basic units of heredity
(genes) The number of chromosomes varies from
one species to another fruit flies 8 humans 46
horses 64
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Modern Thinking

• During the 1930s and 1940s,
• paleontologists, population biologists,
  geneticists, and others developed ideas that
  merged to form a modern synthesis or
  neo-Darwinian view of evolution
• They incorporated chromosome theory of
  inheritance into evolutionary thinking
• They saw changes in genes (mutations) as only one
  source of variation

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Most Importantly

• They completely rejected Lamarcks idea of
  inheritance of acquired characteristics
• They reaffirmed the importance of natural
  selection
• But since then, some scientists have challenged
  the emphasis in modern synthesis that evolution
  is gradual

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The Species

• Species
• a population of similar individuals that in
  nature interbreed and produce fertile offspring
• Species are reproductively isolated from one
  another
• Goats and sheep do not interbreed in nature, so
  they are separate species
• When artifically bred in captivity, offspring are
  most often sterile.

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Remember

• Evolution by natural selection works on variation
  in populations
• most of which is accounted for by the reshuffling
  of alleles from generation to generation during
  sexual reproduction
• The potential for variation is enormous with
  thousands of genes each with several alleles
  (varieties), and with offspring receiving 1/2 of
  their genes from each parent
• New variations arise by mutations
• change in the chromosomes or genes

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Mutations

• Mutations result in a change in hereditary
  information
• ONLY mutations that take place in sex cells are
  inheritable,
• Can be chromosomal mutations (affecting a large
  segment of a chromosome)
• or point mutations (individual changes in
  particular genes)
• Mutations are random with respect to fitness
• they may be beneficial, neutral, or harmful to
  survival!

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The Species

• Species
• a population of similar individuals that in
  nature interbreed and produce fertile offspring
• Species are reproductively isolated from one
  another
• Goats and sheep do not interbreed in nature, so
  they are separate species
• When artifically bred in captivity, offspring are
  most often sterile.

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Recipe for a species

• Speciation is the process by which a new species
  arises from an ancestral species
• It involves change in the genetic makeup of a
  population,
• which also may bring about changes
• in form and structure
• During allopatric speciation,
• species arise when a small part of a population
  becomes isolated from its parent population

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Variations among Darwins finches were
naturally selected from among the existing
variations within the gene pool and mutations
that may have occurred. What would cause the
selection of the observed variations?
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Allopatric Speciation

• Reduction of the area occupied by a species may
  leave a small isolated population
• Two peripheral isolates evolved into new species
  (i.e. Darwins finches)

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How long does it take for changes to appear?

• Although widespread agreement exists on
  allopatric speciation scientists disagree on how
  rapidly a new species might evolve
• Phyletic gradualism- the gradual accumulation of
  minor changes which eventually bring about new
  species

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Punctuated Equilibrium
holds that little or no change takes place in a
species during most of its existence then
evolution occurs rapidly
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Styles of Evolution

• Divergent evolution occurs when an ancestral
  species giving rise to diverse descendants adapts
  to various aspects of the environment
• Divergent evolution leads to descendants that
  differ markedly from their ancestors
• Convergent evolution involves the development of
  similar characteristics in distantly related
  organisms
• Parallel evolution involves the development of
  similar characteristics in closely related
  organisms

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Divergent Evolution
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Convergent Evolution
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Parallel Evolution
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Evolutionary Novelties

• All land-dwelling vertebrate animals posses bone
  and paired limbs so these characteristics are
  primitive and of little use in establishing
  relationships among land vertebrates
• However, hair and mammary glands are derived
  characteristics.
• Only one subclade, the mammals, has them

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It wouldnt be Geology without Death and
Destruction..

• Perhaps as many as 99 of all species that ever
• existed are now extinct
• Organisms do not always evolve toward some kind
  of higher order of perfection or greater
  complexity
• Vertebrates are more complex but not necessarily
  superior in some survival sense than bacteria
• after all, bacteria have persisted for at least
  3.5 billion years
• Natural selection yields organisms adapted to a
  specific set of circumstances at a particular time

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Extinction

• The continual extinction of species is referred
  to as background extinction
• It is clearly different from mass extinction
  during which accelerated extinction rates sharply
  reduce Earths biotic diversity
• Extinction is a continual occurrence
• so is the evolution of new species that usually
  quickly exploits the opportunities another
  species extinction creates
• Mammals began a remarkable diversification when
  they began occupying niches the extinction of
  dinosaurs and their relatives left vacant

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Extinction

• The mass extinction of dinosaurs and other
  animals at the end of Mesozoic Era is well
  knownbut not the greatest loss of biologic
  diversity!
• The greatest mass extinction occurred at the end
  of the Paleozoic Era end of Permian
• More than 90 of all species died out
• We will discuss these extinctions and their
  possible causes throughout the rest of the term

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Some predictions from the Theory of Evolution

• Oldest fossil-bearing rocks should have different
  organisms than more recent rocks
• There should be fossils connecting orders and
  classes of descendant organisms.
• Closely related species should be similar in
  anatomy, biochemistry, genetics
• Classification of organisms should show a nested
  pattern of similarities
• Isolated populations should closely resemble
  nearer populations rather than distant
  ones.Organisms should show a predicted
  succession in the fossil record fish, reptiles,
  mammals
• Animals that diverged from a common ancestor
  should evolve to be more different over time

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Homologous or Analagous?

• Homologous structures
• Similar structure
• Different purpose
• Analagous structures
• Distinctly different structures
• Similar purpose Homologous or analagous? See
  Page 148 Text.
• Forelimb of humans, whales, bats
• Wings of birds, bats, flies

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