You see a piece of meat rotting, and out of it crawls maggots. The meat is changing as it rots: its colour, smell, texture, dampness, etc. are all going through changes. The creation of maggots is just another part of that change, it would seem.
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| (This is a maggot by the way. Don't they look cute and weird up close!) |
If you see this over and over again, in all sorts of contexts, it will seem to you to be true. This is the basis of Aristotelian 'Natural Philosophy', which is the origin of modern science. Repeated observations are key to understanding the world. In fact, in this context, you would have to be quite strange to see anything other than maggots being 'born' from the rotting meat.
It was also Aristotle who brought together the classical theories on spontaneous generation:
"...some [animals] spring from parent animals according to their kind, whilst others grow spontaneously and not from kindred stock; and of these instances of spontaneous generation some come from putrefying earth or vegetable matter, as is the case with a number of insects, while others are spontaneously generated in the inside of animals out of the secretions of their several organs."
Aristotle, History of Animals, Book V, Part 1
Aristotle, History of Animals, Book V, Part 1
Aristotle had seen many examples of 'spontaneous generation' with his own eyes, and he described the 'vital heat' which must exist in some things and lead to life arising there. Hundreds of years later, with the invention of microscopes, and the stronger emphasis on experimentation over observation in science, people began to get another idea.
If you're interested in the history of the microscope and its use to understand the generation of life, there's an interesting blog post that goes into lots of detail: Invisible World. (There's also a shorter, but still quite comprehensive article here.) The summary of it is that though the microscope was invented in around 1610, the matter of spontaneous generation was not entirely settled until Pasteur's experiments in 1859. In those 250 years, there was plenty of back and forth, and attempts at experiements to prove one side or the other to be correct.
The best thing by far to have arisen from the debate is this recipe for how to make a mouse by Jan Baptista van Helmont:
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| (Wheat + sweaty rags + 21 days = fully grown mice) |
It's such a great idea that it's even the kicking off point for a short story by Jon Franklin: To Make a Mouse.
Overall, it seems that it's very hard to let go of something that you can see to be true with your own eyes. Understandably so.
I'm fairly certain that if future discoveries turn our understanding about reproduction on its head, it would probably take another quarter of a century for us to get on board.
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