2 “The secret to reaching my goals lies solely in my tenacity” -Louis Pasteur
3 Abiogenesis vs. Biogenesis Introduction:Biology as a Science progressed by observation.The hypotheses proposed by early scientists were rarely tested by experiments.
4 Abiogenesis continued… Example:Pond dries up – no fish or frogsRain comes – fish and frogsTherefore: It rained fish and frogs
5 Abiogenesis 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
6 Van 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!
9 Redi 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.
10 Redi 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…
11 Needham John Needham (1713 – 1781) English botanist Reexamined theory of AbiogenesisObserved meat broth left unsealed soon changed colour (evidence of microorganisms).
12 Needham continued… Experiment: Boiled flasks of meat broth to kill microorganismsLeft the flasks (unsealed)Flasks soon become murky and full of microbes
13 Needham continued… Conclusion: Abiogenesis AHHHHHHHHH!!! Sent many Scientists down the wrong path.
14 Lazzaro Spallanzani (1729-1799) 25 years later Spallanzani repeated experiment more carefullyBoiled flasks longer and sealed flasksCritics again objected to sealed flasks!
15 The Final Blow! Louis Pasteur (1822-1895) 1864 – Pasteur developed a swan-neck flask
16 Pasteur continued… Experiment: Boiled broth, air could enter but microbes were trapped in curved flaskBroth remained clear Biogenesis finally proven!