“Hence without parents by spontaneous birth
Rise the first specks of animated earth”
– E. Darwin, 1803
Spontaneous generation is the idea that life can arise from non living material at any given moment and one of the earliest references I found to the concept was from Anaximander in the 3rd century BC. Not long after, Aristotle was writing in the 4th century about eels. They troubled him as he could find no trace of their sex. He concluded that eels “proceeds neither from pair, nor from an egg” but that instead they were born of the “earth’s guts”, that is spontaneously emerging from mud. Aristotle believed that worm casts were actually embryonic eels boiling out of the ground. Pliny the Elder had another idea, that eels would rub themselves against rocks and the scrapings would come to life. Other eel theories included young emerging from the gills of fish, from dew or being created by electrical disturbances. The reason that eels caused natural history such issues is because of their lifecycle which starts out at sea, away from the eyes of man.
Aristotle also thought that spontaneous generation applied to a few other creatures, often small, including flies and frogs, which were considered to be lower life forms. Some were thought to be produced in putrefying mud and dung, in wood, in excrement, and dew. Later, naturalists would claim that insects spontaneously generated out of old wax, vinegar, damp dust and books. Even decaying larger animals were thought to generate these smaller lifeforms. Horses were thought to be transmogrified into hornets, crocodiles into scorpions, mules into locusts and bulls into bees. Rats were said to come from garbage, aphids from bamboo, flies from sweat and ants from sour wine.
Athanasius Kircher included ‘recipes’ for life in his 1665 book, for example, to create frogs, you needed to collect clay from a ditch where frogs have lived, incubate it in a large vessel, add rainwater and voila!
Jan Baptist van Helmont in the 17th century tells us how to make poisonous, predatory arachnids; fill a hole in a brick with basil, cover with a second brick and leave in the sun. To make mice, he instructs us to place wheat and water in a flask, cover with the skirt of an unclean woman, leave for 21 days and there you’ll have baby mice. Another mouse suggestion was that they emerged from the earth and in some places you could see them fully formed as far as the breast and front feet, the rest still just mud.
To make flies, you collect fly cadaver’s, crush them slightly, put them on a brass plate and sprinkle with honey water. You can make bees by killing a bull, putting the corpse on branches and herbs during spring and by summer you’d have your bees. Oysters would grow from slime, cockles from sand and salamanders from fire.
Whilst all of this sounds absurd to us today, if you put yourself in their shoes, I think you’d struggle to find a better theory. After all, caterpillars don’t have parents that resemble them, and when they die (turn into a chrysalis), they create a butterfly. Mushrooms grow from dead logs, mould appears out of nowhere and then there are the ‘annual’ fishes of Africa and South America:
“Their lifestyle is almost magical. They live in puddles, ponds and ditches that dry up for part of the year. When the puddles dry up, they die. Only their eggs survive, buried under the dried mud, waiting for the next rains. Collect mud, add water – and presto, you get fish. You can see why people believed in spontaneous generation.”
– Olivia Judson
Over time, the idea of spontaneous generation began to be questioned. In 1646 a sceptic was ridiculed for questioning the idea but Francesco Redi would seek to disprove the idea that maggots grew out of raw meat with experiments in the 17th century (he still believed that living matter could create other living matter eg trees creating wasps and gallflies). Unfortunately, his results were questioned, holes were poking in the methods and John Needham would go onto ‘prove’ via another experiment that spontaneous generation was of course real. Needham’s experiment took gravy and heated it, then sealed the end of the flask and the idea was that nothing could survive the heat or get it as it was sealed. When life started to form, Needham was validated in his belief. However, he hadn’t heated the flask high enough to kill the bacteria enclosed in it so they survived the process.
Other people would work at disproving spontaneous generation including Lazzaro Spallanzani who built on the work of Redi, but it wasn’t until Louis Pasteur came onto the scene in the 19th century that the theory was conclusively disproved.
Ultimately, by investigating the theory of spontaneous generation, we would come across pasteurisation and the field of microbiology would be born.