Descent with Modification

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Descent with Modification
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Title page from The Origin of Species
Published November 24, 1859
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Theory

• Because of the difference between the scientific
  and common usage of the word theory , many people
  fail to appreciate the extensive evidence that
  supports most scientific theories. For example,
  nearly every scientist accepts the theory of
  evolution as fully supported scientific truth
  all species change with time, new species are
  formed and older species die off.. Although
  evolutionary biologists debate the details of how
  evolutionary processes bring about these changes,
  very few scientists doubt that the theory of
  evolution is essentially correct.
• Moreover, no scientist who has tried to cast
  doubt on the theory has ever devised or conducted
  a study that disproves any part of it
• Unfortunately confusion about the usage of the
  word theory has led to endless public debate
  about supposed faults and inadequacies in the
  theory of evolution

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Two Big Themes

• Species evolved from ancestral species and were
  not specifically created as is
• Natural Selection is the mechanism that could
  account for evolutionary change

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Aristotle
Scala naturae He saw a range of complexity of
living things and attempted to arrange them on a
ladder of complexity
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Creationist-essentialist dogma

• Natural Theology

DOGMA The established belief or doctrine held by
a religion, ideology, or organization thought to
be authoritative and not to be disputed.
For natural theologians, adaptations of organisms
were evidence that the Creator had designed every
species perfectly for a particular purpose
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Linnaeus
Father of Taxonomy Developed the Binomial
nomenclature system
"God creates, Linnaeus disposes"
(17071778)
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Georges Cuvier (1769-1832)
Founded science of Paleontology. The fossil
record provided evidence that the Earth had seen
a succession of flora and fauna. Geology revealed
that the Earth was ancient.
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Castastrophism

• Catastrophism theory that major changes in the
  Earths crust are the result of catastrophic
  events rather than from gradual processes of
  change
• Cuvier used catastropism to explain appearance of
  new species in more recent rock that were absent
  in older rock by
• Periodic catastrophes result in mass extinctions
• After extinctions, the region is repopulated by
  different species immigrating in from other areas.

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Fossils of trilobites, animals that lived in the
seas hundreds of millions of years ago
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James Hutton (1726-1797)

• Father of modern geology. He saw the Earth as a
  living machine, immensely old and powerful with "
  ...no vestige of a beginning, no prospect of an
  end."
• Gradualism. Principle that profound change is the
  cumulative product of slow continuous processes

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Strata of sedimentary rock at the Grand Canyon
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Formation of sedimentary rock and deposition of
fossils from different time periods
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Jean Baptiste Lamarck (1744-1829),
Believed that evolution was driven by an innate
tendency toward increasing complexity
(perfection)
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Lamark

• Lamarks proposed mechanism of change
• Use and Disuse
• The body parts used extensively to cope with the
  environment become larger and stronger, while
  those not used deteriorate
• Inheritance of Acquired Characteristics
• The changes an organism acquired during its
  lifetime could be passed along to its offspring

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The historical context of Darwins life and ideas
DARWIN
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Charles Darwin in 1859, the year The Origin of
Species was published
Darwin Video
1809 -1882
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Darwin as an ape
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The Voyage of HMS Beagle
Darwin (age 22) left England in 1831 for a 5-year
round-the-world voyage as ship naturalist
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Galápagos finches
2 populations of a species could be isolated in
different environments and diverge as each
adapted to local conditions. Over many
generations, the two populations could become
dissimilar enough to be designated as separate
species.
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Origin of Species

• Descent with Modification
• There is unity in life with all organisms related
  through descent from some unknown ancestral
  population that lived in the remote past.
• Modifications (adaptations) accumulated over
  millions of years, as descendents from this
  common ancestor moved into various habitats

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Descent with modification elephant lineage
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Origin of Species

• Natural Selection
• I have called this principle, by whicheach
  slight variation, if useful, is preserved, by the
  term Natural Selection. Charles Darwin from
  "The Origin of Species
• Artificial selection has been and continues to be
  extensively practiced by humans

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Artificial selection

• All these vegetables have been selected from a
  single species of wild mustard.
• By selecting different natural variations in
  particular plant parts plant breeders have
  obtained very different end results

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Origin of Species

• Natural Selection
• Darwin's theory of evolutionary selection holds
  that variation within species occurs randomly and
  that the survival or extinction of each organism
  is determined by that organism's ability to adapt
  to its environment

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Natural Selection

• Observation 1
• All species have such great fertility that their
  population size would increase exponentially if
  all individuals that are born would reproduce
  successfully
• Observation 2
• Most populations are normally stable in size
  except for seasonal fluctuations
• Observation 3
• Natural resources are limited

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Natural Selection

• Inference 1
• Production of more individuals then the
  environment can support leads to a struggle for
  existence among individuals of a population, with
  only a fraction of offspring surviving each
  generation

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Natural Selection

• Observation 4
• Individuals of a population vary extensively in
  their characteristics no 2 individual are
  exactly alike
• Observation 5
• Much of this variation is heritable

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Natural Selection

• Inference 2
• Survival in the struggle for existence is not
  random, but depends in part on the hereditary
  constitution of the surviving individuals. Those
  whose inherited characteristics fit them best to
  their environment are likely to leave more
  offspring than less fit individuals.
• Inference 3
• This unequal ability of individuals to survive
  and reproduce will lead to a gradual change in a
  population, with favorable characteristics
  accumulating over the generations

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Natural Selection

• Natural selection is this differential success in
  reproduction, and its product is adaptation of
  organisms to their environment
• Environmental editing
• The environment favors some variations over others

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Validations of the Darwinian view of life

• Direct observations of evolutionary change

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Evolution of insecticide resistance in insect
populations
1.Spraying of poisons to kill insects favors
survival/reproductive success of insects with
inherent (genetic) resistance to the poisons 2.
Resistant individuals survive and pass along the
gene for resistance to offspring. 3. Addition
applications of the same insecticide are less
effective and the frequency of resistant insects
in the population grows
Natural Selection in action
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Natural Selection In Galapagos Finches
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Evolution of drug resistance in HIV
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Validations of the Darwinian view of life

• The Fossil Record The succession of fossil
  forms linking modern life to ancestral forms. New
  missing links are discovered regularly to
  complete the picture.
• Fossil evidence shows the chronology of the
  appearance of vertebrates as
• Fishes ? amphibians ? reptiles ? birds ? mammals

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Whale evolution from terrestrial ancestor
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Validations of the Darwinian view of life

• Comparative anatomy
• Homologous structures (structures that are
  similar because of a common ancestry)
• Example Forelimbs of mammals are constructed of
  the same skeletal elements. The basic similarity
  is the consequence of descent from a common
  ancestor and that the limbs have been modified
  (DESCENT WITH MODIFICATION) for different
  functions.
• Vestigial organs (historic remnants of structures
  that had important functions in ancestors)

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Homologous structures anatomical signs of
descent with modification
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Vestigial structures
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Convergent evolution
Closely related organisms share characteristics
because of common descent. Some distantly related
organisms can resemble each other due to
Convergent Evolution
Sugar glider (Australian marsupial) and Flying
Squirrel (N. American placental mammal)
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Validations of the Darwinian view of life

• Biogeography geographic distribution of
  species. Species tend to be more closely related
  to other species from the same area than to other
  species with a similar way of life but living in
  different areas.

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Validations of the Darwinian view of life

• Comparative embryology
• Closely related organisms go through similar
  stages in their embryonic development
• Example of embryonic homology- gill slits
• Form gills in fish
• Form Eustachian tube in humans

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Validations of the Darwinian view of life

• Molecular biology
• Siblings have a greater similarity in their DNA
  and proteins than do 2 unrelated people.
• Similarly, 2 species that are closely related
  have a greater of their DNA and proteins in
  common than more distantly related species

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Molecular Data and the Evolutionary Relationships
of Vertebrates
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Evolution is not a theory

• Evolution. The conclusion that species change,
  that life has evolved is a historical fact.
  Evidence for which is everywhere.
• Darwins theory of natural selection as the means
  by which the evolution occurs is a theory.
• It is strong and unifying explanation which has
  stood the test of time and much experimentation.