Spontaneous Generation

• Biology


  The science of life and living organisms
• Spontaneous generation


  The hypothetical process by which living organisms develop from nonliving matter
• For much of history, people believed that animals could come from non-living sources
• Beliefs about spontaneous generation

  • Frogs developed from falling drops of rain
  • Mice arose from sweaty underwear
  • Flies arose from decaying meat
• Authorities

  • People believed what they were told by "authorities" such as the Church, or the ancient Greek philosopher Aristotle
  • Many people believed this idea since they simply accepted what they were told, specifically by the authorities
• Aristotle


  A Greek philosopher who first proposed that life could arise from non-living matter if the material contained "pneuma" or vital heat
• Jan Baptista van Helmont


  A Flemish scientist that put forth the idea that mice could appear out from wheat kernels and rags left out in an open container for 3 weeks
• Recipe for mice


  1. Put a soiled shirt and grains of wheat in a jar and let them ferment

  2. Mice form after 21 days
• Francisco Redi


  Italian physician & poet who attempted to disprove the theory of spontaneous generation
• Redi's experiment

  1. Involved two jars and decaying meat: one with a wax seal and the other left in the open

  2. Wax sealed vessels failed to produce maggots whereas decaying meat left in the open were full of them
• Redi concluded that "The flesh of dead animals cannot engender worms unless the eggs of the living being deposited therein."
• Redi's critics said


  • You have too many variables
  • There is a lack of access and a lack of air
  • We ALL know that everything needs air
  • Of course no flies grew!
  • You haven't proven anything
• Redi's 2nd experiment


  1. He covered the jars with fine mesh

  2. Flies laid eggs on the mesh and no maggots were able to reach the meat

  3. He concluded that "All living beings come from seeds of the plants or animals themselves."
• John Needham


  English Clergyman who wondered whether the idea of spontaneous generation applied to microbes
• Needham's experiment


  1. Prepared various broths and showed that they contained microbes

  2. Then he boiled them and showed that there were no longer any microbes

  3. He ensured the stoppers were loose, so that air would not be excluded

  4. Then, after a few days, microbes had reappeared

  5. He concluded that microbes spontaneously generated from the non-living broth
• Needham's error was that microbes could have come from the air
• Lazzaro Spallanzani


  Italian Naturalist who rejected Needham's conclusions and claimed that he didn't seal the jars well enough, and microbes could have come from the air
• Spallanzani's 1st experiment

  1. Repeated Needham's experiment but boiled the broth a little longer and sealed it shut (hermetically sealed - absolutely airtight)

  2. No growth of microbes was seen
• Spallanzani's 2nd experiment


  1. Did time boilings and left some jars, as Needham had, with leaky seals to ensure "active principle" was not damaged

  2. Boiling did not damage the broth's ability to support life

  3. Growth depended on the seal only
• Louis Pasteur


  French chemist who entered a contest sponsored by French Academy of Sciences to prove or disprove Spontaneous generation
• Pasteur's experiment

  1. Used swan-necked flasks, which allowed the entry of air but trapped microbes along its neck

  2. Showed no growth after many days

  3. Pasteur showed that the active principle was not damaged

  4. At any later time, he could tip the flask, this allowed nutrient broth to contact the dust and carry microbes into the broth