What is the Origin Of Life? Part-4 (Theory of Biogenesis or disprove/refute of spontaneous generation)

Theory of Biogenesis or disprove/refute of spontaneous generation:

 Some scientists were skeptical of the spontaneous generation hypothesis, especially in later decades. The debate over spontaneous generation continued well into the nineteenth century (1861), with scientists serving as proponents of both sides. To settle the debate, the Paris Academy of Sciences offered a prize for the resolution of the problem. Louis Pasteur, a prominent French chemist who had been studying microbial fermentation and the causes of wine spoilage, accepted the challenge. Meanwhile Rudolf Virchow in 1858 first mentioned publicly the concept of biogenesis. Some histories on the establishment of biogenesis theory are mentioned below.

i) Rudolf Virchow (Proponent of Biogenesis): In 1858, Rudolf Virchow challenged spontaneous generation with his concept of biogenesis. He claimed that “living cells can arise only from pre-existing living cells”. This concept would somehow explain the origin of animalcules seen under a microscope. The problem with Virchow is that he did not have any experiments to prove his concept. However, 3 years later in 1961, this concept was proven luckily by Louis Pasteur through a series of experiments.

ii) Louis Pasteur: In 1861, the French scientist Louis Pasteur resolved the issue of the origin of microbes (“animalcules") through a series of ingenious and persuasive experiments. Louis Pasteur designed an experiment to show that biogenesis was true even for Microorganisms. Pasteur made two experiments to prove the verity of the theory of biogenesis.

a) Pasteur’s first experiment: Pasteur’s first experiment involved flasks and beef broth. He filled a number of short-necked flasks with beef broth and then boiled their contents. He left some of flasks in open air to cool down while he immediately sealed other flasks. After few days, the contents of the unsealed flasks were found to be contaminated with microorganisms. No evidences of growing microorganisms were found on the sealed flasks. Pasteur concluded that the microorganisms in the air were responsible for contaminating non-living matter like the broths in John Needham’s flask.

 

Figure 3 (a) Photo of Louis Pasteur, (b) Photo of Pasteur’s swan-neck flask (long S-shaped tube), (c) A drawing of Pasteur’s experiment disproving the theory of spontaneous generation of life. Pasteur’s experiment consisted of two parts. i) The top diagram shows the swan-neck flask- containing broth that is being boiled to kill microorganisms in the broth. No contamination occurs ii) The bottom diagram shows the same flask being boiled. Next, the swan-neck is removed and the flask is opened to the environment. When the neck of the flask is broken off, bacteria reach the sterile broth, and organism growth occurs. This is seen as cloudiness in the broth. 

 

ii) Pasteur’s second experiment: To further prove his point, Pasteur performed another experiment with flasks and broth but this time he put beef broth in open-ended long-necked flasks. He bent the necks of the flasks into S-shaped curves and boiled the contents of the flasks. Amazingly, the contents of the flasks were not contaminated by microorganisms even after several months. He correctly predicted that sterilized broth in his swan-neck flasks would remain sterile as long as the swan necks remained intact. Pasteur's flask remained free of bacterial growth for as long as the flask remained upright. The unique S-shaped design of Pasteur’s flasks allowed air to pass but hindered microorganisms from entering inside of the flask. This has been occurred due to the entrapment of microorganisms inside the S-shaped neck of the flask. Hence he was able to prove that microorganisms do not come from inanimate things, such as the air. He demonstrated that air is not capable of producing microbes through his experiment. Through his experiments Pasteur permanently discarded the spontaneous generation hypothesis.

However, should the necks be broken?

When the neck of the flask was broken, microorganisms would be introduced, contaminating the flasks and allowing microbial growth within the broth. Pasteur’s set of experiments irrefutably disproved the theory of spontaneous generation and earned him the prestigious Alhumbert Prize from the Paris Academy of Sciences in 1862. In a subsequent lecture in 1864, Pasteur articulated “Omne vivum ex vivo” (“Life only comes from life”). In this lecture, Pasteur recounted his famous swan-neck flask experiment, stating that “life is a germ and a germ is a life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment.

What is Origin of Life, part-1 (Introduction and Historical Development)  

What is Origin of Life, part-2 (Introduction and Historical Development)  

What is the Origin of Life? Part-3 (Theory of spontaneous generation/Theory of abiogenesis)