The Evolution of Life

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The Evolution of Life

• Chapter 8

Nature does nothing uselessly. -- Aristotle
(384 BC - 322 BC)
"Nothing in biology makes sense except in light
of evolution" --Theodosius Dobzhansky, 1930
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The Misconceptions

• Biologists disagree about the premise of
  evolution
• Some scientific evidence is against evolutionary
  theory
• Evolutionary theory states that humans evolved
  from chimpanzees
• Evolution is speciation
• Evolution has never been observed
• Darwin invented the concept of evolution

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Antecedents of Evolutionary Thought

• Aristotle 384-322 BCFather of animal biology
  set down basic principles of taxonomy and
  relatedness among life believed that complexity
  evolved from additive simplicity, not created de
  novo continuity of organization unity of plan.
• Buffon 1760s similarity of form among closely
  related groups in spite of function led to
  believe in common ancestry, not individual
  creations.

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Antecedents of Evolutionary Thought

• Lamarck 1800 1st to propose a mechanism of
  evolutionary change Acquired Characteristics
  by changing ones physical form throughout a
  lifetime, those changes will be carried on to
  future generations wrong in thinking that
  individuals are capable of evolving and animals
  and plants get what they need evolutionarily

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Charles Darwin and Adaptation

• Darwin developed his theory of evolution by
  natural selection by carefully observing nature,
  especially during his voyage around the world on
  the H.M.S. Beagle.

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Galapagos Islands

• Darwins Finches
• Why such tremendous diversity?
• Why similarities to mainland, but many more
  species?
• Islands are species poor, but for those present,
  incredible diversity of forms.
• Molecular analysis today shows Darwin to be right
  that all of these forms descended from a single
  ancestor finch species

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Charles Darwin and Evolution

• The Basis of the Darwinian Theory
• Organisms are adapted somewhat to their
  environments
• Organisms reproduce more offspring than can
  possibly survive
• Populations are variable phenotypically and
  genetically
• Some individuals in natural populations reproduce
  more than others

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Charles Darwin and Natural Selection

• Evolution as fact Natural Selection as
  mechanism.
• Darwin, after almost 23 years of study, that
  included developmental biology, biogeography,
  anatomy, physiology, cell biology, agriculture,
  animal breeding, geology, and geography, to
  synthesize a single theory that encompasses all
  of life.

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Charles Darwin and Adaptation

• 1840. Malthus and Population Growth
• Human Food Production grows arithmetically,
  whereas Human Population Growth is exponential.
  Concluded humans will outgrow their food supply
  and struggle for survival.
• Darwinian Fitness Differential Reproductive
  Success
• Natural Selection works at the level of phenotype
• It is the interrelationship between mutation and
  natural selection that drives populations

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Darwin the Synthesizer
Homology Richard Owen, ancestry of form shows
shared evolutionary history
Earnst Haeckel Ontogeny Recapitulates
Phylogeny. Wrong, but similarity of
developmental patterns showed that characters
evolved from previous characters. There are no
new structures
Molecular biology has fully supported
Evolutionary Theory as laid down by Darwin and
Wallace more than 130 years previously
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Other Data

• Lyells Geology, early 1800s, Age of the earth
  scaled to millions of years
• Vestigial Structures no reason for their
  presence except in the context of evolution of
  form
• Extinction of some forms against the Theological
  stance of fixity of species
• Animal husbandry an breeding through artificial
  selection
• Islands!! Patterns of biogeography explained by
  natural causation not consistent with creation

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All organisms contain some vestigial structures
that give clues to the past.
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Still More Data
Gray Wolf Ancestor to all dogs

• Extinction of some forms against the Theological
  stance of fixity of species
• Animal husbandry and breeding through artificial
  selection
• Islands!! Patterns of biogeography explained by
  natural causation not consistent with creation

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And Still More

• Convergent adaptations of unrelated organisms
  living in similar environments. Strong support
  for natural selection as a mechanism of
  evolutionary change

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And more

• Intermediate Forms

Extinct Archaeopteryx
Living Platypus
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Age of the Earth
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Alfred Russell Wallace

• Worked in the Amazon in late 1700s
• Worked in the Malay Archipelago early 1800s
• Sent a manuscript to Darwin a fellow naturalist
  who he had heard about
• Set the wheels of exposure in motion for the
  unveiling of a new theory of life on Earth
• Together with Darwin presented to the world The
  Theory of Evolution

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The Darwinian Revolution

• Mid 19th century Both Charles Darwin and Alfred
  Russell Wallace independently derive a new
  mechanism of evolutionary change based upon the
  following observations
• Organisms are adapted to their environments
• Populations have variation in characters
• More offspring are produced than can possibly
  survive
• Individuals with certain characters reproduce
  more than others

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Natural Selection

• Evolution is Theory, Change through time is a
  fact of nature
• Natural selection is the Darwinian Mechanism of
  evolutionary change
• It functions by favoring those individuals in
  populations that produce the most offspring and
  have offspring that survive to reproduce
• Therefore, only populations can evolve, as
  characters that facilitate reproductive fitness,
  perpetuate some individuals over others
• Characters that are selected for change over time

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Contemporary Evidence of Evolution
Darwinian Medicine Leading medical schools are
now (finally) teaching courses of Darwinian
evolution to potential MDs so that they
understand the long-term consiquences of their
actions. Case in Point Antibody resistance has
evolved as predicted by Darwinian evolution and
threatens the ability of our medical industry to
be able to combat infectious diseases due to the
evolved immunity of greater proportions of
bacterial populations.
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Contemporary Evidence of Evolution
Darwin and Wallace predicted mechanism would be
found that maintain and promote variation in
populations and that these mechanisms would be
random in nature. Today we know these mechanisms
to be mutation, recombination after crossing
over, and independent assortment of alleles that
result in unique haploid cells and unique
offspring after fertilization.
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Contemporary Evidence of Evolution
Darwin predicted that if his ideas survived the
test of time, that the Earth would be found old
enough to allow for the relatively slow pace of
evolutionary change to occur Today we use
various mechanisms of chemical breakdown and
conversion to support this assertion.
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Contemporary Evidence of Evolution
Darwin in his book The Descent of Man, predicted
that humans and primates would be found to be
closely related. Today we can use DNA techniques
to test this hypothesis. The differences between
human DNA and that of Chimpanzees exceeds 98
complimentary sequences.
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Descent with Modification
Groups that are closely related show similar, but
not identical anatomies
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Descent with Modification
Very similar, but modified anatomy of humans from
that of other apes shows a close ancestral
relationship, but also that the selective
pressures on hominids differed from those of
other apes. In particular, the favoring of
adaptations for upright posture in hominids.
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Speciation a special consideration

• Speciation involves the evolution of one species
  from another (Darwins decent with modification)
  through long expanses of time (several thousand
  to millions of years).
• The conditions for this to happen are very
  specific.
• It involves the reproductive isolation of groups
  for long periods of time.
• This isolation leads to divergence in characters,
  behaviors, and genes.
• If isolated long enough, when populations come
  back in contact (sympatry) they no longer
  recognize each other as the same breeding unit or
  gene pool.
• There are several way that speciation can occur,
  but it is thought that Allopatric (geographic
  isolation) is the predominant method.

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Allopatric Speciation
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Adaptive Radiations An explosion of new species
over relatively short periods of geologic time, a
few million years. Usually follws a mass
extinction event
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Speciation in hominids can be traced by an
exquisite fossil record. Current fossil data
support the Out-of-Africa hypothesis making the
origin of Homo sapiens evolution in Africa and
later migrating to other continents.
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Mitochondrial DNA studies are used to trace the
maternal inheritance through family lineages, but
can be used also to trace the maternal
inheritance of all of humanity.
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Mitochondrial DNA studies have traced the origins
of all humans to the ancestral Eve who evolved
in Africa. All humans in essence are African,
but lineages have diversified in subspecies
(races) after migrating to different regions of
the Earth where selection pressures differed.
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Hominid Evolution Current Picture
http//www.mnh.si.edu/anthro/humanorigins/ha/a_tre
e.html