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Abiogenesis & the Invisible World. Science progresses by observation. To “set the scene”. Observations are often FLAWED by INTERPRETATIONS that attempt to explain what was observed. Scientists often propose explanations (hyptheses) in an attempt to interpret natural events.
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Abiogenesis & the Invisible World Science progresses by observation...
To “set the scene”... • Observations are often FLAWED by INTERPRETATIONS that attempt to explain what was observed. • Scientists often propose explanations (hyptheses) in an attempt to interpret natural events. • Hypotheses proposed by early scientists were almost never tested by experiment. • Often, one unsubstantiated hypothesis became the basis for another & scientists moved further & further from the truth...
Great philosopher of ancient Greece • Theory of Abiogenesis: states that nonliving things can be transformed into living things spontaneously (sometimes called “spontaneous generation”). • Aristotle’s theory was accepted for nearly 2000 years! Aristotle “frogs and fish did not fall from the sky but came from the mud…”
Jean van Helmont • Only 300 years ago • concluded that “mice could be created from grains of rice & a sweaty shirt within 21 days…” • “the sweat in the shirt caused the wheat to ferment…..” • “the bubbling wheat eventually transformed into mice” Until now, science had been based on logical analysis rather than on experimentation….
Francesco Redi (1668) • Tested hypothesis that rotting meat could transform into flies • “I placed bits of eel, snake, fish, & veal in four different jars…” • “open set = experimental group” • “closed jars = control set” • critics claimed that the “active ingredient” (air) was not permitted into the sealed jars where no flies appear • “I experimented with fine mesh tops…”
Antony van Leeuwenhoek (1632-1723) • Expert lens maker • Remarkable observant scientist • His “scopes” were the first to reveal microorganisms & human blood cells!
John Needham (1713-1781) • Re-examined theory of spontaneous generation • Observed: meat broth left unsealed soon changed color & gave off a putrid smell… • Tested his hypotheses through experimentation… • Boiled flasks with meat broth in LOOSELY sealed flasks for a few minutes to kill microbes • After a few days the murky contents were examined under a microscope… • The broth was FULL of microbes! • Needham rushed to retest the experiment…using different types of broths…. • Microbes continued to appear…. • Needham concluded that this was a result of spontaneous generation…
Lazzaro Spallanzani (1729-1799) • 25 years after Needham’s experiments… • By prolonging the heat and more carefully sealing the vessels, Spallanzani was able to show that such broths generated no microorganisms as long as the vessels remained sealed. • Abiogenesis did NOT occur!
Louis Pasteur (1822-1895) • The FINAL BLOW to the theory of abiogenesis… • Swan-necked flask • Boiled broth for a long time • Microbes became trapped in the curve of the glass!
Emergence of the Cell Theory… • That’s another class!
