Spontaneous Generation

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Spontaneous Generation
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There are two versions of the idea

• Abiogenesis Some life forms arose spontaneously
  from non-living matter in the past or can arise
  in the present time
• Heterogenesis From organic material you can get
  well-organized forms of life. For this case it
  was thought it occurred primarily in decaying
  matter

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Seventeenth Century Recipes

• Place sweaty underwear and husks of wheat in an
  open-mouthed jar, wait for about 21 days, the
  sweat from the underwear would penetrate the
  husks of wheat, changing them into mice
• Another dry hay in water and 2 days later
  microorganisms

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A Very Old, Popular Idea

• Anaximander of Miletus (ca. 610-546 BCE)
• Hippocrates (ca. 460-370 BCE)
• Aristotle (384-322 BCE)
• St. Augustine, Bishop of Hippo (354-430)
• Roger Bacon (ca.1220-ca. 1292)
• Albertus Magnus (1193-1280)
• Francis Bacon (1561-1626)
• Pierre Louis Moreau de Maupertuis (1698-1759)
• Chevalier de la Marck (Lamarck) (1744-1829)

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Common Thread

• Some of the most important scientists of their
  times believed in it
• Throughout all periods of science history
• All these people shared a materialistic views
  and/or a strong beliefs in evolution

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The First Challenges

• William Harvey
  (1578-1657)
• Ex ovo omnia

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Francesco Redi (Italian, 1626-1697)

• His father was the First Physician of the Grand
  Duke of Tuscany
• Francesco studied in Florence at the Jesuits'
  schools and took a degree in medicine in 1647
• From 1657 to 1667 he was a member of the
  Accademia del Cimento (Academy of the
  Experiment), where the Galilean heritage continued

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• In 1666 Grand Duke Ferdinando II appointed Redi
  as his First Physician and director of the
  grand-ducal "Spezieria" (Pharmacy) positions in
  which he was confirmed by Cosimo III in 1670,
  when he became Grand Duke
• So Redi spent much of his life at the Medici's
  Court and was, after Galileo, a unique example of
  scientist and courtier

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• At that time, it was widely held that maggots
  arose spontaneously in rotting meat
• Redi believed that maggots developed from eggs
  laid by flies
• He set out meat in a variety of flasks, some open
  to the air, some sealed completely, and others
  covered with gauze. Maggots appeared only in the
  open flasks in which the flies could reach the
  meat and lay their eggs
• Despite this, he continued to believe spontaneous
  generation could occur under some circumstances

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• Jar-1
• Left open Maggots developed
• Flies were observed laying eggs on the meat in
  the open jar

• Jar-2
• Covered with netting Maggots appeared on the
  netting
• Flies were observed laying eggs on the netting

• Jar-3
• Sealed No maggots developed

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Anton van Leeuwenhoek (Dutch, (1632-1723)

• Started as an apprentice in a dry goods store
  where magnifying glasses were used to count the
  threads in cloth
• He taught himself new methods for grinding and
  polishing tiny lenses of great curvature which
  gave magnifications up to 270x diameters, the
  finest known at that time

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• These lenses led to the building of Anton Van
  Leeuwenhoek's microscopes considered the first
  practical microscopes
• He was the first to see and describe bacteria
  (1674), yeast, plants, the teeming life in a drop
  of water, and the circulation of blood corpuscles
  in capillaries

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• He used his lenses to make pioneer studies on an
  extraordinary variety of things, both living and
  non-living, and reported his findings in over a
  hundred letters to the Royal Society of England
  and the French Academy
• In 1676 Anton van Leeuwenhoek discovered
  animalicules or infusoria
• They appeared to arise spontaneously

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John Tuberville Needham (English, 1713-1784)

• In 1745 proposed to test whether or not
  microorganisms appeared spontaneously after
  boiling
• He boiled chicken broth, put it into a flask,
  sealed it, and waited microorganisms grew
• He claimed victory for spontaneous generation

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Lazzaro Spallanzani (Italian, 1720-1799)

• A priest and a teacher with no formal training in
  medicine
• In the 1780's suggested that in Needhams
  experiment perhaps the microorganisms had entered
  the broth from the air after the broth was
  boiled, but before it was sealed

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• He modified Needham's experiment he placed the
  chicken broth in a flask, sealed the flask, drew
  off the air to create a vacuum, then boiled the
  broth no microorganisms grew
• Proponents of spontaneous generation argued that
  Spallanzani had only proven that spontaneous
  generation could not occur without air

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The Final Blow

• The French Academy of Sciences sponsored a
  contest for the best experiment either proving or
  disproving spontaneous generation
• By that time abiogenesis was very much out of the
  question
• The question was about heterogenesis of
  microorganism (not even complex forms of life)

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Louis Pasteur (French, 1822-1895)

• A major figure in the history of science
• He was trained as a chemist
• He championed changes in hospital practices to
  minimize the spread of disease by microbes
• He discovered that weakened forms of a microbe
  could be used as an immunization against more
  virulent forms of the microbe

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• He found that rabies was transmitted by agents so
  small they could not be seen under a microscope,
  thus revealing the world of viruses
• He developed techniques to vaccinate dogs against
  rabies, and to treat humans bitten by rabid dogs
• He developed pasteurization, a process by which
  harmful microbes in perishable food products are
  destroyed using heat, without destroying the food

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• In 1859 Pasteur designed an experiment that was a
  variation of the methods of Needham and
  Spallanzani
• He boiled meat broth in a flask, heated the neck
  of the flask in a flame until it became pliable,
  and bent it into the shape of an S
• Thus, air could enter the flask, but airborne
  microorganisms could not they would settle by
  gravity in the neck
• No microorganisms grew

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• When Pasteur tilted the flask so that the broth
  reached the lowest point in the neck, where any
  airborne particles would have settled, the broth
  rapidly became cloudy with life

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• He had both refuted the theory of spontaneous
  generation and convincingly demonstrated that
  microorganisms are everywhere, even in the air
• He still thought that abiogenesis may have been
  possible in a distant past

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Question of the Day

• Are spontaneous generation and Darwinism in
  conflict?