Spontaneous Generation vs. Biogenesis

1. Spontaneous Generation vs. Biogenesis

2. Aristotle (384 - 322 BC) • Proposed the theory of spontaneous generation • Also called abiogenesis • Idea that living things can arise from nonliving matter • Idea lasted almost 2000 years

4. Early Science • For centuries, people based their beliefson their interpretations of what they saw going on in the world around them without testing their ideas • They didn’t use the scientific method to arrive at answers to their questions • Their conclusions were based on untested observations

5. Example of Observations • Observation:Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times

6. Example cont… • Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs

7. Disproving Spontaneous Generation

8. Francesco Redi (1668) • In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide-mouth jars containing meat

9. Redi’s Experiment • Redi used open & closed flasks which contained meat. • His hypothesiswas that rotten meat does not turn into flies. • He observedthese flasks to see in which one(s) maggots would develop.

10. Redi’s Findings • He found that if a flask was closed with a lid so adult flies could not get in, no maggots developed on the rotting meat within. • In a flask without a lid, maggots soon were seen in the meat because adult flies had laid eggs and more adult flies soon appeared.

11. Redi’s (1626-1697) Experiments Evidence against spontaneous generation: 1. Unsealed – maggots on meat 2. Sealed – no maggots on meat 3. Gauze – few maggots on gauze, none on meat

12. Francesco Redi

13. Did Redi Use the Scientific Method?

14. Disproving Spontaneous Generation of Microbes

15. Lazzaro Spallanzani’s (1765) • Boiled soups for almost an hour and sealed containers by melting the slender necks closed. • The soups remained clear. • Later, he broke the seals & the soups became cloudy with microbes.

16. Spallanzani’s Results

17. Conclusion • Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed “vital force” • “Vital force” needed to life to form. • Therefore, spontaneous generation remained the theory of the time

18. Louis Pasteur (1822-1895)

19. Pasteur's Experiment • Hypothesis:Microbes come from cells of organisms on dust particles in the air; not the air itself. • Pasteur put broth into several special S-shaped flasks • Each flask was boiled and placed at various locations

20. Pasteur's Experiment - Step 1 • S-shaped Flask • Filled withbroth • The special shaped was • intended to trap any dust particles containing • bacteria

21. Pasteur's Experiment - Step 2 • Flasksboiled • Microbes Killed

22. Pasteur's Experiment - Step 3 • Flask left at various locations • Did not turn cloudy • Microbes not found • Notice the dust that collected in the neck of the flask

23. Pasteur's Experimental Results

24. The Theory of Biogenesis • Pasteur’s S-shaped flask kept microbes out but let air in. • Proved microbes only come from other microbes (life from life) - biogenesis

25. Review

26. Evidence Pro and Con • 1668: Francisco Redi filled six jars with decaying meat. Conditions: Results: 3 jars covered with fine net - No maggots 3 open jars - Maggots appeared From where did the maggots come? What was the purpose of the sealed jars? Spontaneous generation or biogenesis?

27. Evidence Pro and Con • 1765: Lazzaro Spallanzani boiled nutrient solutions in flasks.

28. Evidence Pro and Con • 1861: Louis Pasteur demonstrated that microorganisms are present in the air.