4 theories: • Spontaneous generation – life can come from nonliving things. • Biogenesis – life only comes from other living things • Cosmogenesis – life on Earth came from another part of our solar system or galaxy • Meteorites contain organic compounds • Conditions necessary for life may have existed on other planets or moons 4. Special creation – all religious beliefs
1668-Francesco Redi • Observed flies land on meat that later develops maggots. • Hypothesis: Maggots come from flies • Experiment control - jars with meat covered experimental – jars with meat open • Results: open jar had flies and maggots • Conclusion: maggots come from flies
Critics said there were no maggots in the closed jar because there was no air! Rediredesigned his experiment and covered the jar with netting. Result: Flies and maggots were on the netting, not in the jar. His hypothesis was correct! First scientist to use a control group
1700’s - Spallanzani Hypothesis: microbes do not come from broth Experiment: Flask with boiled gravy left open – microbes grew Flask with boiled gravy sealed – no growth Critics said “no air “– no redesign
1868 - Pasteur • Redesigned Spallanzani’s experiment using a swan-necked flask • Flask was left open - no growth Critics said “bad broth” • Pasteur broke off the neck and growth began Persevered and proved his point!