This document discusses the historical debate between abiogenesis and biogenesis. It describes early experiments by scientists like Aristotle, van Helmont, and Needham that seemed to support abiogenesis, the idea that nonliving things can spontaneously generate life. However, later experiments by Redi, Spallanzani, and especially Pasteur provided evidence against abiogenesis and in favor of biogenesis, that life only comes from preexisting life. Pasteur's key experiment used a swan-neck flask to definitively disprove abiogenesis and prove biogenesis.

1. Biogenesis vs.
Abiogenesis
Biology 11

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 frogs
 Rain comes – fish and frogs
Therefore: 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 ago
Belgian 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!

7. Redi
 In 1668 Francesco Redi (Italian
physician) tested Aristotle’s hypothesis
(meat  flies)

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 meat
 Conclusion: 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 Abiogenesis
 Observed meat broth left unsealed
soon changed colour (evidence of
microorganisms).

12. Needham continued…
Experiment:
 Boiled flasks of meat broth to kill
microorganisms
 Left 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 carefully
 Boiled flasks longer and sealed flasks
 Critics 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 flask
 Broth remained clear  Biogenesis
finally proven!

18. The End!
Now here is your assignment:
List and explain three “flaws” in experimental design
that you have heard about during this presentation.