2“The secret to reaching my goals lies solely in my tenacity” -Louis Pasteur
3Abiogenesis vs. Biogenesis Introduction:Biology as a Science progressed by observation.The hypotheses proposed by early scientists were rarely tested by experiments.
4Abiogenesis continued… Example:Pond dries up – no fish or frogsRain comes – fish and frogsTherefore: It rained fish and frogs
5Abiogenesis continued… Theory of Abiogenesis(aka spontaneous generation)Nonliving things can be transformed into living things.Proposed by Aristotle who observed rotting meat and flies.Existed for nearly 2000 years
6Van Helmont continued… ~300 years agoBelgian doctor Jean van Helmont – concluded that mice could be created from a dirty shirt.He placed grains of wheat and a dirty shirt in a container and in 21 days mice appeared.Conclusion: Sweat caused wheat to ferment into mice. Abiogenesis!
9Redi continued… 4 sets of jars with meat (snake, eel, fish, veal) one set was open (experimental group)one set was sealed (control group)Maggots appeared on open jars of meatConclusion: Flies come from flies! Biogenesis – life from life.
10Redi continued… Bad news lots of critics No air in jar, therefore life could not survive.Redi repeated his experiment with a fine mesh wire – supported Biogenesis again!Critics still objected…
11Needham John Needham (1713 – 1781) English botanist Reexamined theory of AbiogenesisObserved meat broth left unsealed soon changed colour (evidence of microorganisms).
12Needham continued… Experiment: Boiled flasks of meat broth to kill microorganismsLeft the flasks (unsealed)Flasks soon become murky and full of microbes
13Needham continued… Conclusion: Abiogenesis AHHHHHHHHH!!! Sent many Scientists down the wrong path.
14Lazzaro Spallanzani (1729-1799) 25 years later Spallanzani repeated experiment more carefullyBoiled flasks longer and sealed flasksCritics again objected to sealed flasks!
15The Final Blow! Louis Pasteur (1822-1895) 1864 – Pasteur developed a swan-neck flask
16Pasteur continued… Experiment: Boiled broth, air could enter but microbes were trapped in curved flaskBroth remained clear Biogenesis finally proven!