Theory of Spontaneous Generation
Long before 1900's, people believed that organisms could evolve from non living things. One of the early thinkers who believed that non-living things could spontaneously give rise to living things was Aristotle. For example, it was a common belief that logs gave rise to crocodiles, dirty sewers gave rise to rats, maggots came from dead bodies, wet soil lead to creation of toads, etc. This spontaneous theory of generation had a strong 'belief system' among people over many centuries.
What is Biogenesis Theory?
An amateur microbiologist, Antoni van Leeuwenhoek, observed small organisms in dirty water and some material he scrapped from his teeth. These organisms were called 'animalcules' that we call as protozoans, today. This discovery took Europe by storm and scientists were thrilled to find these animalcules. The most pricking question in the minds of many was about the origin of these animalcules. This doubt had only one answer, spontaneous theory of generation.
Over the years, many intelligent minds came up with theories that defied spontaneous generation theory. An Italian physician, Francesco Redi could prove in 1668 that life cannot evolve spontaneously. Redi created a meat and maggot experiment where he allowed meat to be exposed to the air. Flies came in contact with the meat. A few days later, there were maggots. To prove they did not spontaneously appear from the meat, he covered the meat. Flies came in contact with the cover and maggots appeared on the cover not the meat. However, people who supported biogenesis did not think that Redi's theory was applicable to microbes. Many other scientists continued their attempts to dissolve the spontaneous theory of generation. However, John Needham in 1745, added chicken broth to a flask and allowed it to cool. Then after few days, microbes did grow in the broth, and Needham proposed it a proof of spontaneous theory of generation. Needlam claimed that vital life is needed for spontaneous generation of animalcules. His claim was challenged by Lazzaro Spallanzani in 1768, who repeated the experiment in a sealed container. He found there was no growth in the container.
Then, in 1858, Rudolf Virchow, a scientist challenged the spontaneous generation theory by proposing the theory of biogenesis. He stated, 'living cells can arise only from pre-existing living cells'. This biogenesis theory partly explained the presence of animalcule under the microscope. However, without any concrete scientific evidence, Virchow's biogenesis theory was not accepted by all.
Louis Pasteur and Theory of Biogenesis
Louis Pasteur was one of the most intelligent scientist of his time. He was the first to be able to prove the biogenesis theory. He proposed that the organisms that are not visible to the naked eye are present in air. However, he emphasized on the fact that air did not give rise to living things. He carried out an experiment that would dissolve the spontaneous theory of generation and prove the theory of biogenesis.
In his experiment, Pasteur heated a number of short necked flasks that contained beef broth. After heating the flasks, he immediately sealed the mouths of some flasks and left a few unsealed. Then after a few days, microorganisms were observed in beef broth that was in flasks that were unsealed. The sealed flasks had no microorganisms present in the broth. This proved that the microorganisms were present in the air and could contaminate the beef broth without the seal.
Now, to prove that air did not give rise to organisms, he demonstrated another experiment. He filled long-necked flasks with beef broth and the flasks were bent into S-shaped curves. These flasks were heated to kill any presence of life in the beef broth. Then he left the flasks as they were for a few days without sealing them. This way the air could reach the broth as it was not blocked. After a few days, Pasteur observed the beef broth and found no microorganisms in it. This showed that the air can access the broth, but the organisms are
trapped in the S-shaped neck of the flask and thus are not able to reach it. You can read more on some interesting creation theories and learn about the human evolution.
This simple and ingenious experiment was enough to break an age-old theory of spontaneous generation. The world could now understand the relevancy of biogenesis theory and that only a living thing can give rise to a living thing. Thus, the mystical belief of non living things giving rise to living things was shattered by a simple experiment by Louis Pasteur. In the end, the answer to the question 'what is biogenesis theory' is that all living things will be created only from living things and no other process.
By Batul Nafisa Baxamusa
Published: 5/4/2010
Revised by Mrs. Scott