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Origin of Life. 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. Spontaneous Generation.
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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
Spontaneous Generation • 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
Example #1 • 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
Example #1 • Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs
Example #2 • Observation:In many parts of Europe, medieval farmers stored grain in barns with thatched roofs (like Shakespeare’s house). As a roof aged, it was not uncommon for it to start leaking. This could lead to spoiled or moldy grain, and of course there were lots of mice around.
Example #2 • Conclusion:It was obvious to them that the mice came from the moldy grain.
Example #3 • Observation:In the cities centuries ago, there were no sewers, no garbage trucks, no electricity, and no refrigeration. Sewage flowed down the streets, and chamber pots and left over food were thrown out into the streets each morning. Many cities also had major rat problems and a disease called Bubonic plague.
Example #3 • Conclusion:Obviously, all the sewage and garbage turned into the rats.
Example #4 • Observation:Since there were no refrigerators, the mandatory, daily trip to the butcher shop, especially in summer, meant battling the flies around the carcasses. Typically, carcasses were “hung by their heels,” and customers selected which chunk the butcher would carve off for them.
Example #4 • Conclusion:Obviously, the rotting meat that had been hanging in the sun all day was the source of the flies.
Abiogenesis Recipes • Recipe for bees: • Kill a young bull, and bury it in an upright position so that its horns protrude from the ground. After a month, a swarm of bees will fly out of the corpse.
Abiogenesis Recipes • Recipe for mice: Place a dirty shirt or some rags in an open pot or barrel containing a few grains of wheat or some wheat bran, and in 21 days, mice will appear. There will be adult males and females present, and they will be capable of mating and reproducing more mice.
Francesco Redi (1668) • In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide-mouth jars containing meat
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.
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.
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
Results of Redi’s Experiments • The results of this experiment disproved the idea of spontaneous generation for larger organisms, but people still thought microscopic organisms like algae or bacteria could arise that way.
The Scientific Method • Observation • Hypothesis • Experiment • Accept, Reject, or Modify hypothesis
Step 1 - Observation • There were flies around meat carcasses at the Butcher shop. • Where do the flies come from? • Does rotting meat turn into or produce rotting flies?
Step 2 - Hypothesis • Rotten meat does not turn into flies. Only flies can make more flies.
Step 3 - Testing • Wide-mouth jars each containing a piece of meat were subjected to several variations of “openness” while all other variables were kept the same. • Control group — These jars of meat were set out without lids so the meat would be exposed to whatever it might be in the butcher shop. • Experimental group(s) — One group of jars were sealed with lids, and another group of jars had gauze placed over them.
Step 4 - Data • Presence or absence of flies and maggots observed in each jar was recorded. • Control group – flies entered, laid eggs, & maggots emerged • Gauze covered – flies on gauze, but not in jar • Sealed jars – No maggots or flies on the meat
Step 5 - Conclusion • Only flies can make more flies. In the uncovered jars, flies entered and laid eggs on the meat. Maggots hatched from these eggs and grew into more adult flies. Adult flies laid eggs on the gauze on the gauze-covered jars. These eggs or the maggots from them dropped through the gauze onto the meat. In the sealed jars, no flies, maggots, nor eggs could enter, thus none were seen in those jars. Maggots arose only where flies were able to lay eggs. This experiment disproved the idea of spontaneous generation for larger organisms.
Anton van Leeuwenhoek (1674) • Leeuwenhoek began making and looking through simple microscopes • He often made a new microscope for each specimen • He examined water and visualized tiny animals, fungi, algae, and single celled protozoa; “animalcules” • By end of 19th century, these organisms were called microbes
John Needham (1745) • Showed that microorganisms flourished in various soups that had been exposed to the air • Claimed that there was a “life force” present in the molecules of all inorganic matter, including air and the oxygen in it, that could cause spontaneous generation to occur
Needham’s Results • Needham’s experiments seemed to support the idea of spontaneous generation • People didn’t realizebacteria were already present in Needham’s soups • Needham didn’t boil long enough to kill the microbes
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.
Conclusion • Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed “life force” • Therefore, spontaneous generation remained the theory of the time
How Do Microbes Arise? • By 1860, the debate had become so heated that the Paris Academy of Sciencesoffered a prize for any experiments that would help resolve this conflict • The prize was claimed in 1864 by Louis Pasteur, as he published the results of an experiment he did to disproved spontaneous generation in microscopic organisms
Pasteur's Problem • 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
Pasteur's Experiment - Step 1 • S-shaped Flask • Filled withbroth • The special shaped was intended to trap any dust particles containing bacteria
Pasteur's Experiment - Step 2 • Flasksboiled • Microbes Killed
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
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 Figure 1.3
Evidence Pro and Con • 1668: Francisco Redi filled six jars with decaying meat.
