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History of LifeChapter 14

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Aristotle (384 –322 BC)Aristotle (384 –322 BC)

•Proposed the theory of Proposed the theory of spontaneous generationspontaneous generation

•Also called abiogenesisAlso called abiogenesis

•Idea that Idea that living things living things can arise from nonliving can arise from nonliving mattermatter

•Idea lasted almost Idea lasted almost 2000 2000 yearsyears

+Spontaneous GenerationSpontaneous Generation

For centuries, people based their For centuries, people based their beliefs on their interpretations of beliefs on their interpretations of what they saw going on in the world what they saw going on in the world around them without testing their around them without testing their ideasideas

They They didn’t use the scientific methoddidn’t use the scientific method to arrive at answers to their to arrive at answers to their questionsquestions

Their conclusions were based on Their conclusions were based on untested observationsuntested observations

+Example #1Example #1

ObservationObservation: Every year in the spring, : Every year in the spring, the Nile River flooded areas of Egypt the Nile River flooded areas of Egypt along the river, leaving behind along the river, leaving behind nutrient-rich mud that enabled the nutrient-rich mud that enabled the people to grow that year’s crop of people to grow that year’s crop of food. However, along with the muddy food. However, along with the muddy soil, large numbers of frogs appeared soil, large numbers of frogs appeared that weren’t around in drier timesthat weren’t around in drier timesConclusion:Conclusion: muddy muddy soil gave rise to the soil gave rise to the frogsfrogs

+Example #2Example #2 Observation:Observation: Since there were no Since there were no

refrigerators, the mandatory, daily refrigerators, the mandatory, daily trip to the butcher shop, especially in trip to the butcher shop, especially in summer, meant battling the flies summer, meant battling the flies around the carcasses. Typically, around the carcasses. Typically, carcasses were “hung by their heels,” carcasses were “hung by their heels,” and customers selected which chunk and customers selected which chunk the butcher would carve off for them. the butcher would carve off for them.

Conclusion: the rotting the rotting meat that had been meat that had been hanging in the sun all hanging in the sun all day was the source of day was the source of the flies. the flies.

+Spontaneous GenerationSpontaneous Generation RecipesRecipes

Recipe for bees:Recipe for bees:

Kill a young bull, and bury it in an Kill a young bull, and bury it in an upright position so that its horns upright position so that its horns protrude from the ground. After a protrude from the ground. After a month, a swarm of bees will fly out month, a swarm of bees will fly out of the corpse. of the corpse.

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Disproving Disproving Spontaneous Spontaneous GenerationGeneration

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Francesco Redi Francesco Redi (1668)(1668)

In 1668, Francesco In 1668, Francesco Redi, an Italian Redi, an Italian physician, did an physician, did an experiment with experiment with flies flies and wide-mouth jars and wide-mouth jars containing meatcontaining meat

His His hypothesishypothesis was was that rotten meat that rotten meat does not turn into does not turn into fliesflies

Redi’s ExperimentRedi’s Experiment

One Jar contained meat exposed to both air and flies

Results: Found maggots that hatched into flies

A second jar contained meat in a container wrapped in a fine cloth so that the meat was exposed to air, but not flies

Results: No flies

A third jar was sealed and thus not exposed to either air or flies

Results: No flies

+Results of Redi’s Results of Redi’s ExperimentsExperimentsThe results of this experiment The results of this experiment disproved the idea of spontaneous disproved the idea of spontaneous generation for larger organismsgeneration for larger organisms

People still thought microscopic People still thought microscopic organisms like algae or bacteria organisms like algae or bacteria could arise that way.could arise that way.

****Wide-mouth jars each ****Wide-mouth jars each containing a piece of meat were containing a piece of meat were subjected to several variations of subjected to several variations of “openness” while “openness” while all other all other variables were kept the same.variables were kept the same.

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Disproving Disproving Spontaneous Spontaneous Generation of Generation of

MicrobesMicrobes

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Lazzaro Lazzaro Spallanzani Spallanzani

(1765)(1765)

Conducted an Conducted an experiment where he experiment where he boiled soups for boiled soups for almost an hour and almost an hour and sealed containers by sealed containers by melting the slender melting the slender necks closednecks closed.

His hypothesis was that microorganisms formed not from the air but from other microorganisms

+Spallanzani’s experiment Experimental group – Boiled broth for several

hours to kill all the microorganisms in the broth and inside of the containerThen: melted the necks of the containers shut while broth still hot

Control group – Boiled broth for several hours to kill all the microorganisms in the broth and inside of the container•Broth became contaminated and cloudy

•Broth would remain microbe free. However, when the flask was opened growth would occur

+Results of Spallanzani’s Results of Spallanzani’s experimentexperiment

ConclusionConclusion: Boiled broth became contaminated only when microorganisms from the air entered the flask

Critics said Spallanzani heated the Critics said Spallanzani heated the flasks too long, destroying the “vital flasks too long, destroying the “vital force” found in the air inside them.force” found in the air inside them.

Air lacking “vital force”, they Air lacking “vital force”, they claimed, could not generate life. claimed, could not generate life. Therefore, spontaneous generation Therefore, spontaneous generation was kept alive for another centurywas kept alive for another century

+Warm up question

1. What does the 1st sealed flask contain?

2.How does the broth change during the experiment?

Broth is boiled

1 yr passes, broth remains clear

Flask is opened

One day passes, broth becomes cloudy

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Louis Pasteur Louis Pasteur (1822-1895)(1822-1895)

Pasteur put broth into Pasteur put broth into several special several special S-S-shaped flasksshaped flasks

Hypothesis:Hypothesis: Microbes Microbes come from cells of come from cells of organisms on dust organisms on dust particles in the air; particles in the air; not the air itself.not the air itself.

+Pasteur’s Experiment Pasture filled beakers with broth and Pasture filled beakers with broth and

curved the neck to create curved the neck to create S-shaped Flasks S-shaped Flasks that trapped any dust particles containing that trapped any dust particles containing bacteriabacteria

After boiling the broth to kill any microbes present the broth remained uncontaminated indefinitelyIf the neck was broken the broth became cloudy and contaminated with a day

+The Theory of BiogenesisThe Theory of Biogenesis

Pasteur’s S-shaped flask kept Pasteur’s S-shaped flask kept microbes out but let air in.microbes out but let air in.

Proved microbes only come from Proved microbes only come from other microbes (life from life) - other microbes (life from life) - biogenesisbiogenesis

Activity- Earth’s timeline

4.6 ByaFormation of Earth

3 Bya1st Photosynthetic bacteria

4Bya

3Bya

2Bya

1Bya

3.8 Bya1st Life

800 MyaMulticellular Organisms

300 MyaInvasion of land

250 Mya1st flowering Plants

65 MyaExtinction of Dinos

20 MyaContinents appear as they do today

160,000 yrsHomo sapiens

15,000 YrsLast Glaciers Recede

2.1 Bya1st Aerobic Bacteria

1.6 Bya1st Eukaryotes

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