THE SCIENTIFIC THEORY OF EVOLUTION

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THE SCIENTIFIC THEORY OF EVOLUTION

• The Unity of Life Explained

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What is a theory?

• Scientists - a theory is the grandest synthesis
  of a large and important body of information
  about some related group of natural phenomena.
• Non-scientists - a theory is s dubious notion
  such as evolution is just a theory
• I will use theory as a body of knowledge and
  explanatory concepts that seek to increase our
  understanding of a major phenomenon of nature.

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Can our theory be disproved?

• Theories are never disproved - only improved.
• Some small parts of a theory my be disproved or
  change but the large concept will never change.
• One can acknowledge the usefulness of a theory
  even though the ultimate causes of the phenomena
  to which it applies are unknown.

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What are the questions?

• How could one account for the extraordinary
  amount of organic diversity?
• How could one explain the remarkable adaptations
  of living creatures?
• What is the basis of the scale of nature, that
  saw all species of animals or plants as part of a
  continuum that, with small gaps, appeared to
  extend from the simplest to the most complex
  species?

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How does one seek the answers?

• Divine Creation - described in Genesis where God
  created all living things and the earth and
  cosmos. Many believe around the year 4004 BC.
• The remarkable adaptations were a result of care
  exhibited by the Creator.
• The scale is explained by saying He created it
  that way.
• The developed into Natural Theology meant to
  explain the work of the Creator.

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ARISTOTLE

• Where Aristotle differed most sharply from
  medieval and modern thinkers was in his belief
  that the universe had never had a beginning and
  would never end it was eternal. Change, to
  Aristotle, was cyclical water, for instance,
  might evaporate from the sea and rain down again,
  and rivers might come into existence and then
  perish, but overall conditions would never
  change.

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Jean Baptiste Lamarck

• What Lamarck actually believed was more complex
  organisms are not passively altered by their
  environment. Instead, a change in the environment
  causes changes in the needs of organisms living
  in that environment, which in turn causes changes
  in their behavior. Altered behavior leads to
  greater or lesser use of a given structure or
  organ use would cause the structure to increase
  in size over several generations, whereas disuse
  would cause it to shrink or even disappear.

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Thomas Malthus

• What "struck" Darwin in Essay on the Principle of
  Population (1798) was Malthus's observation that
  in nature plants and animals produce far more
  offspring than can survive, and that Man too is
  capable of overproducing if left unchecked.
  Malthus concluded that unless family size was
  regulated, man's misery of famine would become
  globally epidemic and eventually consume Man.

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Charles Lyell

• In his Principles of Geology (3 volumes,
  1830-33), Lyell conclusively showed that the
  earth was very old and had changed its form
  slowly, mainly from conditions such as erosion.
  Lyell was able to date the ages of rocks by using
  fossils embedded in the stone as time indicators.
• Popularized uniformitarianism
• States that geologic laws present today also
  existed in the past.

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Charles Darwin

• A British naturalist who took a five year voyage
  on the HMS Beagle to map and collect life forms.
• This allowed Darwin to study a wide variety of
  diverse organisms.
• Explained evolution in terms of natural selection

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The affinities of all the beings of the same
class have sometimes been represented by a great
tree. I believe this simile largely speaks the
truth. The green and budding twigs may represent
existing species and those produced during each
former year may represent the long succession of
extinct species... The limbs divided into great
branches, and these into lesser and lesser
branches, were themselves once, when the tree was
small, budding twigs and this connection of the
former and present buds by ramifying branches may
well represent the classification of all extinct
and living species in groups subordinate to
groups... From the first growth of the tree, many
a limb and branch has decayed and dropped off,
and these lost branches of various sizes may
represent those whole orders, families, and
genera which have now no living representatives,
and which are known to us only from having been
found in a fossil state... As buds give rise by
growth to fresh buds, and these, if vigorous,
branch out and overtop on all a feebler branch,
so by generation I believe it has been with the
great Tree of Life, which fills with its dead and
broken branches the crust of the earth, and
covers the surface with its ever branching and
beautiful ramifications" (Darwin, 1859).
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Natural selection is based upon

• Overproduction
• Struggle for existance
• Variation
• Survival of the fittest
• Origin of new species by inheritance of
  successful variations.

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Who is Alfred Wallace?

• A naturalist who also promoted the theory of
  natural selection.
• He forwarded a manuscript to Charles Darwin.
• Darwin presented his thoughts and those of
  Wallace at a meeting in 1858.
• Darwins thesis was published in 1859.
• Many refer to it as the Darwin-Wallace theory of
  evolution because both came up with the idea at
  almost the same time in history.