Biogenesis vs. Spontaneous Generation

Fundamental Questions 1.Where do we come from? 2.How did life start on Earth? 3.What were our ancestors like millions of years ago? 1

Science vs. Society No one can say with absolute certainty and proof that they have the answers to these questions. Religions, cultures, communities and schools of thought often clash with their answers to these questions – intense and long-standing debates arose. 2

Why Science? In a scientific investigation, a method is used : The Scientific Method. Hypotheses are proposed, tested, and evaluated. If the evidence is irrefutable, it is commonly accepted. If not, it is not. This doesn’t indicate TRUTH, just ACCEPTANCE. 3

Has Science Always Agreed? The best thing about science is that it can change based on new discoveries and new evidence. 4

5 Spontaneous Generation For centuries, people based their beliefs on 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

6 Examples of Spontaneous Generation

7 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

8 Example #1 Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs

9 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.

10 Example #2 It was obvious to them that the mice came from the moldy grain. Conclusion: It was obvious to them that the mice came from the moldy grain.

11 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.

12 Example #3 Conclusion: Obviously, all the sewage and garbage turned into the rats Conclusion: Obviously, all the sewage and garbage turned into the rats.

13 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.

14 Example #4 Obviously, the rotting meat that had been hanging in the sun all day was the source of the flies. Conclusion: Obviously, the rotting meat that had been hanging in the sun all day was the source of the flies.

15 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.

16 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.

Biogenesis says that in nature, life comes from previously existing life of its own kind. Every single science experiment ever done in Biology suggests this to be true. But in the past, in fact as late as the 1700s, the dominant theory was abiogenesis, or spontaneous generation. Use your own device to find the meaning of the phrase “spontaneous generation.” Fill in the section in your note templates.

18 Spontaneous Generation For centuries, people based their beliefs on 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

Disproving the idea of Spontaneous Generation

20 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 copyright cmassengale

Theophrastus ( BC)

Paracelsus ( )

Timeline DRAW a sketch for each experiment and write 1 sentence of the conclusion that can be drawn

26 Disproving Spontaneous Generation

27 Francesco Redi

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

29 Redi’s Experiment Redi used open & closed flasks which contained meat. His hypothesis was that rotten meat does not turn into flies. His hypothesis was that rotten meat does not turn into flies. He observed these flasks to see in which one(s) maggots would develop. He observed these flasks to see in which one(s) maggots would develop.

30 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.

31 Redi’s ( ) 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

32 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.

Pier Antonio Micheli (1729) His Nova plantarum genera (1729) was a major step in the knowledge of fungi. He discovered the spores of mushrooms.

Pier Antonio Micheli (1729) He observed that when spores were placed on slices of melon the same type of fungi were produced that the spores came from. This observation led to the discovery that fungi did not arise from spontaneous generation.

35 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

36 Needham’s Results Needham’s experiments seemed to support the idea of spontaneous generation. People didn’t realize bacteria were already present in Needham’s soups. Needham didn’t boil long enough to kill the microbes

37 Needham’s Experiment

38 Lazzaro Spallanzani’s (1765) Boiled soups for almost an hour and sealed containers by melting the slender necks closed 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.

39 Spallanzani’s Results

40 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

41 The Theory Finally Changes

42 How Do Microbes Arise? By 1860, the debate had become so heated that the Paris Academy of Sciences offered 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

43 Louis Pasteur ( )

44 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

45 Pasteur's Experiment - Step 1 S-shaped Flask Filled with broth The special shaped was intended to trap any dust particles containing bacteria

46 Pasteur's Experiment - Step 2 Flasks boiled Flasks boiled Microbes Killed Microbes Killed

47 Pasteur's Experiment - Step 3 Flask left at various locations Did not turn cloudy Did not turn cloudy Microbes not found Notice the dust that collected in the neck of the flask

48 Pasteur's Experimental Results

49 Pasteur’s S-shaped flask kept microbes out but let air in. Proved microbes only come from other microbes (life from life) - biogenesis The Theory of Biogenesis Figure 1.3

What about today? The current acceptance is that life comes from other life (biogenesis), but the ultimate question is : Where did the FIRST life come from? 50