The Development of Evolutionary Theory

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The Development of Evolutionary Theory

• A Brief History of Evolutionary Thought

Physical Anthropology Spring 2006
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A Brief History of Evolutionary Thought

• The individual most responsible for the
  elucidation of the evolutionary process was
  Charles Darwin.
• However, the theory of Natural Selection was
  independently developed by another Englishman
  Alfred Russel Wallace.
• Medieval concept of statsis
• all aspects of nature including all forms of life
  and their relationships to one another, were seen
  as fixed and unchanging.
• Christianity was taken quite literally.
• God had created all life forms exactly as they
  existed in the present.
• Alterations were seen as impossible because they
  would have run contrary to Gods plan. This
  belief is know as fixity of species.
• The notion that species, once created, can never
  change.

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• Great Chain of Being.
• the belief that all Gods creations were arranged
  in a hierarchy that progressed from the simplest
  organisms to the most complex
• First proposed by Aristotle
• The Earth was full and that nothing new (such
  as species) could be added.
• Grand Design that is Gods design (the
  universe).
• Argument for design
• anatomical structures were viewed as planned to
  meet the purpose for which they were required.
• Archbishop James Ussher (1581-1656)
• The date the Grand Designer started his work was
  at noon on Sunday, October 23, 4004 B.C.
• The prevailing notion of the Earths brief
  existence, together with fixity of species,
  provided a formidable obstacle to the development
  of evolutionary theory WHY?

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• What, then, upset the medieval belief in a rigid
  universe of planets, stars, plants, and animals?

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The Scientific Revolution

• The discovery of the New Word and the
  circumnavigation of the globe in the 15th century
  overturned some very fundamental ideas about the
  planet.
• Earth was round
• awareness of biological diversity
• Copernicus heliocentric model challenged
  Aristotles geocentric model
• Heliocentric model further supported by Galileo
• Other notables, Keppler, Decartes, and Newton
  establishing the laws of physics, motion and
  gravity.
• In essence, the scientific achievements
  increasingly came to direct as well as reflect
  the changing views of Europeans.

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The Path to Natural Selection

• John Ray (1627-1705)
• Defined the concept of species.
• Ray also recognized that species frequently
  shared similarities with other species.
• He labeled this group genus.
• However, Ray was an adherent of fixity of
  species.
• His 1691 publication, The Wisdom of God
  Manifested in the Works of Creation, was intended
  to demonstrate Gods plane in nature.
• He stressed the deliberate outcome of the Grand
  Design.

Ray is often referred to as the father of natural
history in Britain.
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• Carolus Linnaeus (1707-1778)
• One of the leading naturalists of the 18th
  century.
• He is best known for developing a classification
  of plants and animals
• The System of Nature (Systema Naturae) in 1735.
• Binomial Nomenclature.
• He added two more categories
• Class
• Order
• His four-level system for classification became
  the basis for taxonomy, the system used today.
• Inclusion of humans into the classification
  system into the genus Homo, and species sapiens.
• While he was a believer in the fixity of species,
  this view did change in his later years based on
  the mounting evidence to the contrary.

Carolus Linnaeus. Portrait by Per Krafft (The
University of Uppsala Art Collections).
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• Comte de Buffon (Georges-Louis Leclerc
  1707-1788)
• He believed neither in the perfection of nature
  nor in the idea that nature had purpose as
  declared by the argument from design.
• He did recognize the dynamic relationship between
  the external environment and living forms.
• Natural History (1749)
• repeatedly stressed the importance of change in
  the universe, and he underlined the changing
  nature of species.
• Migrating groups would be influenced by and adapt
  to the environment.
• He rejected the idea that one species could give
  rise to another.

Comte de Buffon, portrait by Garnerey del., P. M.
Alix sculpt. Paris, chez Drouhin.
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• Erasmus Darwin (1731-1802)- Grandfather of
  Charles Darwin. Freethinking high living
  physician was well known in literary circles.
• Zoonomia
• evolutionary concepts were expressed in verse.
• Erasmus Darwin had expressed similar views on
  natural selection.
• Charles was fond of his grandfathers writings
  however, it is not known how much he was
  influences by them.

Erasmus Darwin, grandfather of Charles Darwin
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• Darwin's interests extended well beyond the
  practice of medicine.
• Dissatisfied with Linnaeus's theory of the
  immutability of species and instead proposed the
  gradual evolution of animals and plants.
• Zoonomia or the Laws of Organic Life (1794).
• This work has been called "the first consistent
  all-embracing hypothesis of evolution."
• The publications of his French contemporaries,
  Cuvier and Lamarck, strengthened Darwin's
  position and provided the foundation for later
  studies in the field, most notably for that of
  Charles Darwin, grandson of Erasmus.

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• Jean-Baptiste Lamarck (1744-1829)
• the 1st European scientist who attempted to
  explain the evolutionary process.
• Lamarck went beyond the views of Buffon by trying
  to explain how species could change.
• Organic forms could become altered in the face of
  changing environmental circumstances.

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• Therefore, as the environment changed, so too did
  the animals activity pattern.
• This resulted in the increase and decrease use of
  certain body parts.
• As a result of use or disuse, body parts became
  altered.
• Physical alterations occurred as a function of
  perceived bodily needs.
• A trait acquired by an animal during its lifetime
  can be passed on to offspring.
• Inheritance of acquired characteristics or
  use-disuse theory

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• Georges Cuvier (1769-1832)
• Most vehement opponent of Lamarck.
• Specialized in vertebrate paleontology
• Introduced the concept of extinction to explain
  the disappearance of animals represented by
  fossils.
• He never grasped the concept of nature and was a
  proponent of fixity of species.

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• Instead of assuming the similarities between
  certain fossil forms and living species indicated
  by evolutionary relationships, Cuvier proposed a
  variation of the theory know as catastrophism.
• held that the earths geological features were
  the results of sudden, worldwide cataclysmic
  events.
• To be consistent with the fossil evidence, Cuvier
  proposed that destroyed regions were repopulated
  by new organisms of a more modern appearance and
  that there forms were the results of more recent
  creation events.
• This account avoided the notion of evolution
  while still explaining change through time.

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• Charles Lyell (1797-1875)- He was a barrister by
  training and a geologist by avocation.
• He is considered to be the founder of modern
  geology.
• He was for many years friend and mentor to
  Charles Darwin.
• Principles of Geology (1830-33)
• Uniformintarianism- he argued that the geological
  process observed in the present as the same as
  those that occurred in the past.

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• This theory flew in the face of Cuviers
  catastrophism.
• Lyells theory implied immense geological time
  scale.
• He changed the framework within which scientists
  viewed the geological past.
• This the concept of deep time remains one of
  Lyells most significant contribution to the
  discovery of evolutionary processes.

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• Thomas Malthus (1766-1834)- an English clergyman
  and economist.
• An Essay on the Principle of Population
• which inspired both Darwin and Wallace in their
  separate discoveries.
• Malthus pointed out that if not kept in check by
  limited food supplies, human population growth
  could double in size every 25 years.
• That is, population size increases exponentially
  while food supplies remain relatively stable.