What is the Theory of Biogenesis?

The theory of biogenesis claims that living things could only arise from living things. The opposite of this theory is the spontaneous generation theory, which states that living things arise from nonliving things. This article will give a brief history of the theory of biogenesis and the spontaneous generation theory. What did early scientists like Louis Pasteur do to attest or contradict the two theories on the origin of living things?

Spontaneous Generation Theory

Until the early 1900s (before Pasteur’s time), people generally believed that organisms arise from non-living objects. Aristotle was among the early thinkers who believed that living things spontaneously arise from things that are not alive. He and most of the people believed that putrid matter give rise to fleas, dirty give rise to rats, rotting logs in water bodies give rise to crocodiles, dead human body give rise to maggots, wet soil give rise to toads, snakes, and mice, and among others. The spontaneous generation has been a “belief system” among people for many centuries. Thanks to the birth of Louis Pasteur and other intelligent scientists.


Antoni van Leeuwenhoek Discovery

Antoine van Leeuwenhoek (Image from Wikimedia Commons)

Using a simple single lens microscope, Antoni van Leeuwenhoek observed small organisms in dirty fluids and materials scraped from his teeth. He called these small organisms “animalcules”. These animalcules are what we call now as protozoans (e.g. amoeba, paramecium, etc.) His discovery spread widely in Europe during his time (1673 and beyond). People and scientists were amazed with the animalcules. The biggest question at that time is the origin of these animalcules. Sadly, the spontaneous generation was used (by scientists) to explain the origin of the tiny organisms seen under the Leeuwenhoek’s microscope.

Rudolf Virchow: Proponent of Biogenesis

Rudolf Virchow (Image from Wikimedia Commons)

In 1858, scientist Rudolf Virchow challenged the spontaneous generation with his concept of biogenesis. He claimed “that living cells can arise only from preexisting living cells”. This concept would somehow explain the origin of animalcules seen under a microscope. Although Virchow was correct with this concept, he lacked the needed experimental evidences demonstrating his concept of biogenesis. In science: to see is to believe.

Louis Pasteur’s Contribution to the Theory of Biogenesis

Louis Pasteur (Image from Wikimedia Commons)Louis Pasteur was the first scientist to provide experimental evidences that non living things cannot give rise to living things. He proposed that the air contains living organisms naked to the eye but emphasized that the air can not give rise to living things. To prove this, he heated a number of short-necked flasks containing beef broth. After heating, he immediately sealed the mouths of some of the flasks while he left the others opened. After few days, microorganisms appeared in the beef broth at the unsealed flasks while no organisms were found in the sealed flasks. Pasteur said that microorganisms present in the air had contaminated the beef broth in the flasks without seal.

To demonstrate that the air cannot give rise to organisms, he performed another experiment. He filled long-necked flasks with beef broth and bent the flasks’ necks into S-shaped curves. He heated all the flasks to kill whatever organism present in the beef broth. He observed the flasks for few days. (Note that air can reach the beef broth because the flasks are not sealed.) After few days of observation, Pasteur observed that no living organisms have grown in the beef broth. He explained that the air can access the beef broth but microorganisms in the air cannot. The microorganisms are trapped in the flask’s S-shaped neck.

Pasteur’s ingenious experiments changed how the world understand the origin of a living thing. He successfully disproved the idea that mystical forces in nature have the ability to generate living things from non living things spontaneously.


Louis Pasteur and the Theory of Biogenesis

Spontaneous Generation Hypothesis

The Germ Theory of Disease