Evolution

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Evolution

• Nothing in biology makes sense
• except in the light of evolution.
• Theodosius Dobzhansky, 1975

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Evolution Was An Idea Whose Time Had Come
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Western Culture Resisted Evolutionary Views of
Life

• Classical Greeks Influenced Christianity Deeply
• Plato
• Dual world - Essentialism
• Aristotle
• Ladder of Nature
• Aristotelian purpose

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Plato (427-347 BC)

• Essentialism Idealism. Existence is divided
  into two worlds
• (1) The real world is ideal and eternal ...Ideal
  Form perfect and forever unchanging, somewhere
  beyond Earth in the world of Forms
• (2) The illusionary world of imperfection that
  we inhabit and that we perceive through our
  senses.
• i.e., as if each of us is like a flawed mirror
  reflecting the True or Ideal human

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Aristotle (384-322)

• Was a student of Plato, although he
  challenged Platos concept of a dual world, he
  was a student of nature and recognized a that
  organisms exhibited a range of complexity
• (1) Scala Naturae the Ladder of Nature
• all living things fit into a perfect order, from
  matter to plants, to animals, to man, to angels,
  and then finally to God. All steps of the ladder
  of nature are filled and unchanging.
• therefore species are fixed, permanent, and do
  not evolve
• (2) Aristotelian purpose
• the goals for which things happen ...drives
  toward perfection
• as opposed to the operation of blind mechanisms
  ...cause and affect sequences of events

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Forces of Change

• Exploration of new lands revealed staggering
  biodiversity
• Fossil record discovered

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Fossil Deposition
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Fossil Record

• a) first thought to be fashioned by erosion or
  man
• b) then realized that fossils are remains of
  living things
• c) distinctive fossils are found in specific
  layers of rock

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Fossil Record

• d) rock layers always found in the same sequence
  (always A above B, B above C, etc., where ever
  those layers are found)
• e) fossils reveal a remarkable progression of
  forms from one layer to the next

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Fossil Record

• Fossil record revealed EXTINCTIONS
• (1) Cuvier (1769-1832 father of paleontology
• anti-evolutionist) documented 23 cases
• ...confirmed extinction
• (2) Cuvier suggested that Catastrophism has
  eliminated some specially created species
• but all extant species should show up within
  the fossil record ...falsified
• (3) Louis Agassiz (1807-1873) suggested multiple
  special creations, one after each catastrophe (gt
  50) in order to reconcile Special Creation and
  Extinction

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Geology Provided Evidence that the Earth is
Exceedingly Old

• a) Christian view
• (1) Christianity interpreted that the Earth is
  4000-6000 years old, by counting generations in
  the Bible
• (2) catastrophes must have taken place to
  reconcile all the reshaping of the earth that was
  apparent in such a short time
• b) Geological gradualism. profound change is
  the product of gradual accumulation of small
  changes through the action of wind, water,
  earthquakes, and volcanism over very long periods
  of time
• James Hutton (1726-1797) and Charles Lyell
  (1797-1875)
• c) Geological gradualism influenced biologists
  by indicating the potential importance of slow
  processes over immense time

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Influence of Early Biologists

• Carolus Linnaeus (1707-1778)
• Studied diversity for the greater glory of
  God. Founder of modern taxonomy.
• Developed the binomial nomenclature we use
  today.
• His classification system was hierarchical.
• Not an evolutionist ..Linneaus himself stated
  that
• God creates, Linnaeus arranges

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Influence of Early Biologists

• Comte de Buffon (1707-1788 ...first suggested
  evolution occurred)
• Buffon suggested that the original Creation
  was a pool from which modern species had been
  conceived by Nature and Produced by Time
• (1) but conflicted with the concept that Gods
  creations were perfect
• (2) no mechanism was proposed ...ridiculed by
  Cuvier

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Influence of Early Biologists

• Jean Baptist Lamarck (1744-1829)
• (1) impressed by the progression for forms in
  the fossil record
• (2) proposed change through time ...evolution
• (3) proposed a mechanism (got this wrong)
• (a) molding force ...innate drive for perfection
  (Ladder of Nature) where Aristotle saw one
  Ladder, Lamarck saw many
• (b) Inheritance of acquired characteristics.
  e.g., giraffe necks resulted from many
  generations of neck stretching ...not the
  differential reproductive success of giraffes
  that differ in neck length
• There is no evidence for the inheritance of
  acquired characteristics.
• (4) emphasized evolution , adaptation, great
  periods of time ...deserves credit for these

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generations of stretching produce longer necks
...Lamarckian Evolution
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Darwins Revolution

• (1) Darwin was a naturalist
• (2) Voyage of the Beagle, 5 yr surveying
  expedition, circumnavigated the globe
• (3) Darwin proposed two things
• (a) occurrence of evolution by descent with
  modification i.e., extant species are descended
  within lineages from ancestors
• (b) the proposed mechanism ...Natural Selection

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Darwin's Proposed Mechanism of Evolution

• Populations are composed of many genetic variants
• This is population thinking ...versus
  essentialist thinking
• Natural populations can increase rapidly in size
  (Malthus)
• based on observation of the great fecundity of
  living things
• but population sizes are usually stable and
• natural resources are limited, therefore
• There is a struggle for existence among these
  variants, resulting in differential survival and
  reproduction
• The struggle for survival reproduction is not
  random, but depends on hereditary constitution of
  individuals
• Natural Selection can result in gradual change in
  the composition of a lineage

NATURAL SELECTION non-random differential
reproductive success
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Phenotypic Variation Natural Selection acts on
heritable differences in phenotype that produce
differential reproductive success
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SUMMARY of the Mechanism of Evolution by Natural
Selection

• populations are genetically variable basic
  resource of evolutionary change
• (2) gene pools are screened by natural
  selection, causing "gradual" change in the
  genetic composition of the lineages over
  generations

Population-Environment Interactions Natural
Selection
Sources of Genetic Variability
Gene Pool Genetic Variability
Mechanism of reproduction was unknown then
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Blending InheritanceRare new variants are
diluted by mating each generation, so it is
difficult to see how pools of genetic variability
could be built up in nature with blending
inheritance.Note that the new variant is always
rare and so it is bound to mate with a "normal"
or wild type individual. This problem
led Darwin to mistakenly conclude that new
variants must arise outside of mating, during
development, by genetic assimilation (sensu
Lamarck). This is false.
new "sport", or mutation
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Lamarckian versus Darwinian Evolutionary
Hypotheses
genetic variation is produced in reproduction,
where natural selection operates
successful genotypes are reproduced faithfully
we are locked into the genotype that we are born
with
Inheritance of acquired characteristics - genetic
change during development
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Major Problems faced by Darwinism

• Darwinism was perceived as subverting Christian
  world views and therefore came under attack for
  social reasons
• Darwin didnt know how reproduction worked, how
  sports (mutations) originated and were maintained
• blending inheritance posed problems for
  maintenance of VG
• accepted inheritance of acquired characters to
  explain mutation
• first attempts to measure VG after the
  rediscovery of Mendelism led to erroneous
  conclusion that VG 0 in natural populations.

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Evidence of Evolution

• Biodiversity is immense 14 - 100 million species
  today
• Tropical biodiversity astounded Darwin. He
  discovered gt60 species of beetles in one
  afternoon in a rainforest in South America

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The fossil record provided evidence of change
over time found transitional series at single
localities ...change over time?
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Biogeography

• Why would God create analogous but different
  life forms in different places?
• (1) South American fauna was very distinct from
  European fauna
• (2) still constituents of different SA biomes
  were clearly more closely related to one another
  than to European taxa occupying similar biomes
• (3) SA fossils more similar to SA extant taxa

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Evidence of radiations and adaptation to local
habitats in Galapagos Islands
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Radiations
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Adaptation to Local Conditions
Vegetation exhibited defenses against predation
on islands containing tortoises too
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Evolution in ActionDarwin's Finches
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Comparative Anatomy Provides Evidence for
Evolution

• Convergent Evolution

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Comparative Anatomy Provides Evidence for
Evolution
Homologies Reveal Common Ancestry
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Comparative Anatomy Provides Evidence for
Evolution

• Vestigial Structures show evidence of
  evolutionary change

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Comparative Anatomy Provides Evidence for
Evolution

• Comparative embryogeny provides evidence of
  common ancestry

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Hierarchical Organization of Biodiversity
Reflects Evolution of Lineages

• Bear Clade

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Artificial Selection
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Dogs are all members of the same species but
illustrate the power of artificial selection