Tag Archives: experimental theory

Spontaneous Generation and Experimentation

Insect lifecycle on grapes as illustrated by Merian

Early spring seemed a good time to take a look at not just butterflies but also the less appealing insects too. (I’m having issues with ant swarms in the kitchen, any non-toxic ideas for addressing that, please pass them on!)


Awhile back I mentioned Maria Sibylla Merian’s flower and insect illustrations. Besides connecting insects to host plants she also showed that insects did not just burst into being but had a lifecycle. For its time that was a controversial observation.

Colored copper engraving from Merian’s Insects of Surinam, Plate XLIX


A lot of people, including those involved in studying natural history, believed that ‘lower species’ were spontaneously generated from dead and inorganic matter. For example, flies were believed to rise full grown from rotting meat, fleas from dust, frogs from mud and slime, etc…


These ideas predated Aristotle, who codified them. Like many of his notions they were embraced by Christianity, and only fell out of favor in the mid to late 19th century. (You can see where this would prove problematic for people curious about inherited traits-what inheritance?)


It took centuries of scientific experimentation and observation to put down spontaneous generation. One of the first studies (and perhaps the most elegant) was by Francesco Redi in the 17th century. He had doctorates in medicine and philosophy and was head physician for the Medici Court.


(Digression: Redi was interested in toxicology-not sure if that was a wise or dangerous interest in the Medici Italy! He studied viper venom, proving that rather than being poisonous if ingested it had to be introduced to the blood through a bite to be dangerous, that not all bites were venomous, and that pressure around a wound could prevent venom from spreading to the rest of the body. In modern times an endangered subspecies of Italian viper was named in his honor.)

Vipera aspis francisciredi


His experiments published in 1668 were the first systematic testing of spontaneous generation.


The first experiment involved 6 jars. He added inorganic matter, dead fish, and raw veal to two jars each. One of each type of jar was left open, while the second was covered with fine gauze so that air could circulate but that nothing could get in or out. After several days he discovered maggots in the open jars but none in the gauze covered jars.


For his second experiment her put raw meat into 3 jars. One was left uncovered, one was covered with gauze and the third was sealed with cork. Maggots appeared in the open jar and on top of the gauze that covered the second jar. The maggots on top of the gauze didn’t survive and nothing happened with the sealed jar.

Francesco Redi


(Perhaps we should have a moment of silence for the person who had to clean up after and smell these experiments…)


As a follow up to this experiment he kept the live maggots from the first jar until they metamorphosed into flies. He then put live flies in a jar with raw meat and dead flies in another jar with raw meat and sealed both. Maggots only appeared in the jar sealed with live flies, confirming their lifecycle.


Mindful of the fates of Giordano Bruno (burnt alive) and Galileo Galilei (house arrest for life) Redi managed to present his findings in a manner palatable to the Catholic Church. (Perhaps he managed this by saying that although he disproved spontaneous generation for flies he still believed it possible for other species. It took Louis Pasteur, almost two centuries later, to finally put the nail in that coffin.)


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Filed under Historical Facts and Trivia, Natural Science