Introduction to Biology

Chapter 1, Section 2

History of Scientific Method

Aristotle: Greek philosopher (2300 yag)Explanations based on logic

2 broad classesLiving (biotic)Non-living (abiotic)

History of Scientific Method

Common knowledge:Living things possess a “vital force” that

allows living things to spawn from non-living sources

Theory of “Spontaneous generation”

History of Scientific Method

Common knowledge:Living things possess a “vital force” that

allows living things to spawn from non-living sources

Theory of “Spontaneous generation”

History of Scientific Method

• Francesco Redi (1668) Italian physician– Challenged spontaneous generation

• Observation: meat left in open air produced maggots• Common Knowledge: maggots come from dead meat• Redi’s hypothesis: Flies lay eggs on raw meat, these

eggs turn into maggots.

History of Scientific Method

History of Scientific method

• Redi’s experiment:• 2 glass containers– One covered– One uncovered

• Same type of meat• Same location• Same temperature• Same amount of time

• VARIABLES

History of Scientific Mehtod

• Redi’s Experiment– Findings– The container with a cover (gauze to allow equal

air flow) did not generate any maggots.– Conclusion:• Maggots only appear on meat that has been exposed to

flies.

History of Scientific Mehtod

• Needham (mid 1700s)• Combined Redi’s findings with the research of

Leeuwenhoek.– Leeuwenhoek made the first microscope

• Needham’s experiment– 2 identical containers– Both heated, then allowed to sit at same temperature– Same gravy

History of Scientific Mehtod

• Needham’s Experiment– Findings: gravy was teeming with microbes – Conclusion: Microbes come from gravy– spontaneous

generation

History Of Scientific Method

• Spallanzani (Italian Scholar)– Spallanzani’s Experiment:• 2 identical containers• Same gravy• Heated–One container sealed immediately–Other left open to air

• Left to sit for same amount of time

History of Scientific Mehtod

• Spallanzani’s Experiment:– Findings: Gravy open to air teeming with microbes, while

sealed container had none.– Conclusion: Microbes too small to see had entered the jar

from the air and reproduced in the gravy.

History of Scientific Method

• Pasteur (1881)• Pasteur’s Experiment– Special flask–Boiled broth

History of scientific Method

• Pasture’s Experiment• Findings: Broth was free of microorganisms• Conclusion: So long as broth is protected from

microorganisms broth remains free of life.

History of Scientific Method

• Pasteur’s work lead to other revolutions in science–Nature of food spoilage–Nature of disease

Did I mention History’s Not my thing…. Brain Break!