Foundations of the Modern Theory of Evolution

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Foundations of the Modern Theory of Evolution

• Taxonomy
• Carolus Linnaeus (binomial nomenclature, genus
  and species)
• Fossils
• Paleontology
• Gradualism Geologic theory, profound changes in
  Earths features over the course of
• geologic time are the result of slow, continuous
  processes.
• Uniformitarianism The geologic processes that
  have shaped the planet have not
• changed over the course of Earths history the
  present is the key to the past.
• Charles Lyell described uniformitarianism in
  Principles of Geology (1830).
• Georges Cuvier firmly established the fact of the
  extinction of past life forms. He did not
• believe in evolution.

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• Jean-Baptiste Lamarck developed an early theory
  of evolution, involving acquired
• characteristics traits obtained during an
  organisms lifetime could be passed on to the
  next
• generation. This is not possible based on what we
  now know of genetics and inheritance.
• In several respects, the theory of Lamarck
  differs from modern evolutionary theory.
• Lamarck viewed evolution as a process of
  increasing complexity and "perfection," not
• driven by chance as he wrote, "Nature, in
  producing in succession every species of animal,
• and beginning with the least perfect or simplest
  to end her work with the most perfect, has
• gradually complicated their structure."
• Lamarck also did not believe in extinction for
  him, species that disappeared did so because
• they evolved into different species. It is
  interesting to note, however, that Lamarck cited
  in support of
• his theory of evolution many of the same lines of
  evidence that Darwin was to use in the Origin of
• Species.

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The Modern Theory of Evolution Charles Darwin

• The concept of the gene and the role of DNA was
  unknown.
• Darwins view of life as expressed in The Origin
  of Species (1859) contrasted sharply with the
  traditional beliefs of an Earth that is a) only a
  few thousand years old, b) is populated by forms
  of life that had been created at the beginning
  and c) has remained unchanged ever since.
• Natural selection states that a population can
  change over generations if individuals with
  certain heritable traits in that population
  produce more viable offspring than other
  individuals.
• A population is defined as a group of
  interbreeding individuals who live in a certain
  geographic area it is the smallest unit that
  can evolve. Individuals do not evolve.
• Natural selection can work only on traits that
  are inherited.
• Natural selection depends on the environment

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Charles Darwin

• Descent with modification All living organisms
  are related by descent (i.e., they are evolved)
  from a remote common ancestor

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Descent with modification
What information can you determine from this
cladogram?
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Charles Darwin

• Principles of natural selection
• 1. Within any population, there is genetic
  diversity.

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Charles Darwin

• 2. Individuals have an unequal ability to survive
  and reproduce that results from the interaction
  between individuals and their environment.
  Example English peppered moth

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Charles Darwin

• 3. New species can arise. If the environment
  changes over time, or if individuals of a
  particular species move to a new environment,
  natural selection may result in adaptations to
  these new conditions, sometimes giving rise to
  new species.

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Beak variation in Galápagos finches
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Artificial Selection

• Artificial selection The process by which
  species are modified by humans. Plants and
  animals are specifically chosen to breed with the
  desired goal of producing offspring with a
  specific characteristics.

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Artificial Selection Wild Mustard
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Evidence for Evolution

• Darwins theory explains a wide range of
  observations
• Fossils can be dated to show relationships
  between
• organisms that currently exist and those that
  are extinct
• (bone fragments, the rock in which an impression
  is left).
• Transitional fossils have been found that link
  ancient
• organisms to modern species, just as Darwins
  theory
• predicts.

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Transitional fossil (extinct whale with hindlimb)
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Evidence for Evolution

• Homology related species share characteristics
  resulting
• from a common ancestry.
• Homologous structures are variations on a
  structural
• theme and are anatomical signs of evolution
  (forelimbs of
• bats, humans whales).

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Mammalian forelimbs Homologous structures
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Evidence for Evolution

• Embryo development of a species shows
  evolutionary
• history of the species. The comparison of early
  stages of
• animal development reveals many anatomical
  homologies
• in embryos that are not visible in adult
  organisms.
• Ontogeny recapitulates phylogeny.

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Anatomical similarities in vertebrate embryos
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Evidence for Evolution

• Vestigial structures have no apparent function in
  modern
• organism, but resemble structures their presumed
  ancestors had
• demonstrated in fossil record (pelvis leg
  bones of snakes).

The blind mole rat (Spalax typhlus) has tiny
eyes completely covered by a layer of skin.
Python with vestigial appendage (hind limb bud).
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Evidence for Evolution

• Organisms share many conserved fundamental
  processes and features that are
• widely distributed among species.
• Molecular homologies are shared characteristics
  at the molecular level, such as
• the use of the same genetic code (RNA, DNA,
  replication, transcription,
• translation). Because the code is shared by all
  organisms, it is likely that all
• species descended from a common ancestor.
• In addition, major metabolic pathways (e.g., ATP
  formation) are conserved across
• all three domains of life.

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Protein found in diverse vertebrates
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Evidence for Evolution

• All eukaryotes have similar internal structure
  organization
• Endosymbioic Theory proposes that eukaryotes
  originated when large
• prokaryotes ingested and assimilated smaller
  prokaryotes.
• Evidence for this includes the fact that all
  eukaryotes have mitochondria for
• Energy transformation unlike the DNA found in
  the nucleus, the mitochondrial
• DNA has no contribution from the father, it
  originates solely from the mother
• autotrophs have chloroplasts for photosynthesis
  both mitochondria and
• chloroplasts grow and divide on their own and
  both resemble modern bacteria.
• Porphyridium DNA in the plastids of this red
  seaweed is closer in sequence to
• that of a bacterium than it is to the DNA in the
  nucleus of that seaweed

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Endosymbiotic Theory
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Evidence for Evolution

• Biogeography refers to the geographic
  distribution of a species. Species that live
  closer to one another tend to be more closely
  related than those that do not.
• Example Australia has a diverse population of
  native marsupial mammals but almost no placental
  mammals.