Charles Darwin (1809-1882)

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Charles Darwin (1809-1882) Alfred Wallace
(1823-1913)British Naturalists
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Foundations of Darwinism

• Darwin and Wallace independently came up with a
  credible MECHANISM that could produce
  evolutionary changes
• Both men Stimulated by
• 1. Observations of diversity of life in the
  tropics
• 2. An Essay on the Principle of Population as
  it Affects the Future Improvement of Society
  (1798) by Thomas Malthus (1766-1834).
• Malthus Argued
• Human populations will always expand until
  famine, war, or disease limits growth

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Darwins Early Years

• Mediocre student during early education
• Loved animals and the outdoors
• 1825, entered Edinburgh University to study
  medicine, no stomach for surgery
• Developed fondness for natural science,
  especially Marine Zoology
• Went to Cambridge, to enter the clergy! 

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Darwin, the Naturalist

• Collected beetles!
• At Cambridge, befriended Professor Henslow,
  interested in botany, entomology, chemistry,
  mineralogy, geology
• Henslow persuaded Darwin, after graduation, to
  begin a study of geology
• Arranged for young Darwin to accompany Professor
  Sedgwick on a field trip through North Wales
• Captain FitzRoy invited D to volunteer as
  naturalist on the Beagle, survey ship about to
  leave on round-the-world mapping and collecting
  expedition

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Darwins Voyage on the Beagle

• Read Lyell's The Principles of Geology during
  early weeks
• Investigated geology of places ship visited,
  understood the slow passage of geologic time
• Collected fossil bones and faunal specimens
• 1831-1836 visited Cape Verde Islands, Brazil,
  Tierra del Fuego, Patagonia, Chile, Argentina,
  the Galapagos Islands, Tahiti, New Zealand,
  Australia, Tasmania, Cocos Islands, Mauritius,
  St. Helena, Ascension, and the Azores

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Formation of Darwins Ideas on Natural Selection

• Darwin's journal, The Voyage of the Beagle
  (1839), sold well
• Perceived that SELECTION was key to success in
  breeding domestic plants and animals.
• Read Malthus observed that animals and plants
  struggled for existence and developed habits and
  variations
• it at once struck me thatfavorable variations
  would tend to be preserved, and unfavorable ones
  to be destroyed. The result of this would be the
  formation of new species" (Darwin, 1898, p. 68).
•  

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Alfred Wallace

• Family of Modest Means
• Limited education, worked many jobs
  construction, surveying, assistant to a
  watchmaker, teacher...
• Loved natural history and the outdoors
• With naturalist Henry Bates,
• traveled to Brazil, explored the Amazon, sold
  collections of biological specimens, especially
  insects

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Wallaces Formative Years

• 1848 Wallace and Bates sailed for South America,
  gathered large collections
• 1852 Sailed back to England, ship caught fire
  and sank after 3 weeks! Passengers rescued but
  collections lost!
• 1859 Bates gathered more than 14,000 species in
  Brazil
• 1854 Wallace collected in the Malay Archipelago
  recognized the Archipelago as biologically
  divided by a narrow strait, separating Asian
  fauna from Australian fauna, still recognized as
  Wallace's Line.

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Wallace Forms His Ideas on Natural Selection

• Applied geological idea of uniformitarianism to
  biology
• Charts of a species might look more like a tree
  than a straight line
• No species came into existence unless coexisted
  with another similar species that was its
  predecessor
• 1855 Wrote paper arguing for evolution of
  species, searching for a MECHANISM. Malthus
  inspired him.

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Wallace and Darwin

• June 1858 Wallace drafted his thoughts, sent
  them in letter to Darwin, Darwin was shattered
• July 1858 Joint credit was given to Darwin
  Wallace at Linnaean Society
• The announcement attracted no particular
  scientific or public attention!
• 1859 Darwin worked intensely for the next year
  on his manuscript, On the Origin of Species by
  Means of Natural Selection (1859), sold out on
  day of publication!

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Natural Selection

• Theory of Natural Selection was based on 3
  observations and 2 deductions
•  Observation 1
• Organisms reproduce in a geometric ratio
  (Actually Malthus was wrong reproduction is
  exponential, not geometric)
• Observation 2
• The numbers of any given species tend to remain
  more or less constant through time
• Observation 3
• All living things vary
• Deduction 1
• There is a universal struggle for survival. More
  organisms of each kind are born than can possibly
  obtain food and survive.
• Deduction 2
• Individuals with some kind of advantage have the
  best chance of surviving and reproducing their
  own kind

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Darwins Grand Contribution

• NATURAL SELECTION some individuals are more
  successful at reproducing than others
• Advantageous characteristics become numerous,
  less favorable characteristics disappear
• NS explains how one species transmutes into
  another species
• EVOLUTION became a central organizing concept in
  biology a NATURAL (v. supernatural) process
  could produce a new species!