Biogenesis is the production of life. For much of history, mankind believed in spontaneous generation, but this theory was disproved by experiments conducted by scientists such as Francesco Redi, Lazzaro Spallanzani, and Louis Pasteur. Today, biogenesis is understood through cell biology and reproductive biology.
Biogenesis is the production of life. In Latin, bio means life and genesis means the beginning or origin of. For much of history, mankind thought biogenesis often occurred through spontaneous generation from land or plant matter, coupled with reproduction, which we now know is the only way biogenesis occurs. Anaximenes and Anaxagoras, pre-Aristotle Greek natural philosophers, believed that biogenesis could occur from the action of the Sun on the primordial earth’s slime, a combination of water and earth. A related idea is xenogenesis, which holds that one type of life form can arise from another entirely different life form.
Around 343 BC, Aristotle wrote the book History of Animals which expounded the spontaneous generation theory of biogenesis which would remain dominant for over 2000 years. In addition to including lengthy descriptions of countless species of fish, crustaceans, and other animals, the book also featured Aristotle’s theory of how animals come to be in the first place. Aristotle believed that different animals could arise spontaneously from different forms of inanimate matter: clams and scallops in sand, oysters in mud, barnacles and limpets in rock cavities. However, no one seemed to claim that humans could emerge from spontaneous generation, being superior creatures that can apparently only be produced through direct reproduction by other humans.
As early as 1668, the Italian physician Francesco Redi proposed that higher life forms (microbes) do not arise spontaneously and the idea became more popular, but proponents of spontaneous generation still maintained that microbes arose through these means. In 1745, John Needham, an English biologist and Roman Catholic priest, added chicken broth to a sealed flask, boiled it, waited, then observed microbial growth, pointing to this as an example of spontaneous generation. In 1768, Lazzaro Spallanzani repeated this same experiment, but he removed all the air from the jar and the microbes did not grow in it. This must have been one of the first experiments to definitively disprove spontaneous generation, but the idea that spontaneous generation was false did not spread at the time.
Turning to 1859, the French biologist Louis Pasteur conclusively refuted spontaneous generation. He boiled the beef broth in a gooseneck flask. The gooseneck let in air but not, as the reasoning went, tiny particles from the air. The experiment showed that microbial growth did not occur in the flask until the flask was turned so that particles could fall along the curves, at which point the water rapidly became cloudy, showing the presence of microorganisms. After 2,000 years, the spontaneous generation theory of biogenesis was finally put to rest. Today it has been replaced by cell biology and reproductive biology.
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