-
Period: 510 BCE to
Spontaneous generation theory
It was generally accepted that simple life forms arise spontaneously from non-living matter. Such "spontaneous generation" was a widely accepted fact by scientists and society alike. In the past, limited technology and observation led people to lack understanding of microscopic organisms and their reproduction, and they believed in spontaneous generation based on religious or philosophical beliefs. -
Spontaneous production of scorpions
A seventeenth century recipe for the spontaneous production of scorpions stated:“Carve an indentation in a brick, fill it with crushed basil, and cover the brick with another,so that the indentation is completely sealed.Expose the two bricks to sunlight, and you will find that within a few days, fumes from the basil, acting as a leavening agent, will have transformed the vegetable matter into veritable scorpions.”Scorpions emerged due to basil attraction or nesting suitability in the experiment. -
Redi's experiment
Francesco Redi, an Italian physician and poet, mounted the first serious challenge to spontaneous generation theory in 1668. It was believed that maggots emerged spontaneously in rotting meat, but Redi sought to disprove this through a controlled experiment, like the one in the picture. However, he only tested maggots, leaving open the possibility of spontaneous generation for microorganisms. -
Needham’s rebuttal
Redi's experiment didn't dispel belief in spontaneous generation. The microscope later revealed microorganisms, suggesting spontaneous generation. Some argued it didn't apply to larger organisms, but might for microbes. Needham boiled broth to kill microbes and sealed it. Later, he observed living microorganisms, supporting spontaneous generation and contradicting Redi.This experiment is not correct because contamination may have caused Needham's observation of living microorganisms. -
Criticism from Spallanzani
Spallanzani did not agree with Needham’s conclusion, so he performed hundreds of experiments using heated broth. He didn't find any form of life after his experiment. The difference between his experiment and Needham's one was that Spallanzani checked that there wasn’t any life left after boiling the flask, which discarded the option of the flask not being boiled hot enough. The only option left was that some microorganisms entered the flask which wasn’t well-closed in Needham's experiment. -
Pasteur puts spontaneous generation to rest
Pasteur designed S-shaped bottles, boiled nutrient-enriched broth inside, and observed no life forms for a year. When he tilted the bottle, he observed life forms within days, concluding that contamination came from the air, not spontaneous generation. Pasteur's flask design trapped microorganisms in the curved neck, allowing only sterile air into the flask. He demonstrated that life can only arise from living organisms, not from non-living matter.