If you ever need to pick a fight with a bunch of 17th and 18th century European nerds, I suggest asking them where they think babies come from. That’s almost guaranteed to get them all riled up.
People around the world had been documenting their observations of and theories about reproduction for centuries leading up to the Age of Enlightenment. Without tools like microscopes, these thinkers were limited to collecting data with the naked eye. Despite these limitations, they were able to come up with some truly fantastical ideas.
Some believed in spontaneous generation, which is the idea that life could spring up from just the right mix of ingredients. For example, Jean Baptiste van Helmont believed that you could make mice if you just mixed together some sweaty clothes and wheat in an open container and wait. Twenty-one days late, and boom! You’ve got yourself some mice.
Others believed in biogenesis, or the idea that living organisms could only come from other living organisms. While this was far closer to the truth than spontaneous generation, a great number of creatively incorrect ideas still managed to come out of the biogenesis camp. According to Clara Pinto-Correla in “The Ovary of Eve,” some scientists theorized that giraffes were the result of a camel mating with a leopard, or that llamas were similarly the results of a camel mating with a mule.
While these ideas may sound outlandish, they weren’t completely unreasonable. It’s obvious now that Helmont didn’t create mice, but rather a nice and cozy mouse house. However, he was innovative enough to experiment with mouse creation, and he drew his conclusions from his observations. And while camels are incapable of creating giraffes, successful reproduction had been observed between animals of different species. If a horse and a donkey can produce a mule, it’s not too strange to think a camel and a leopard might produce a giraffe.
(Also, it should be noted that the incorrect ideas are often much more entertaining than the correct ones. I think that should count for something.)
By the mid-to-late 1600s, there were already a diverse set of very strongly held beliefs about the nature of reproduction. Among the subscribers to biogenesis, two main groups were forming – the preformationists and the epigenesists. Drawing on work going all the way back to Pythagoras (yes, the triangle guy), preformationists believed that living things grew from eggs or seeds that contained tiny versions of the fully formed being. For example, inside a chicken egg, there would be a microscopic chicken that would just get bigger and bigger until it was ready to hatch. The epigenesists, however, believed that some form of development occurred before birth.
The debate raged on. Even among preformationists, there were two competing groups who would come to be known as the ovists and the spermists. The ovists believed the preformed being came from the female (in an egg), while the spermists believed it came from the male (in various forms).
Then, in 1677, Antonie van Leeuwenhoek used his microscope to observe sperm for the first time. And that’s when all hell broke loose and people started putting pants on frogs. (Okay, it was only a few people. And only a few frogs. But it’s still a whole lot of fun.)
Enter Lazzaro Spallanzani. Spallanzani was an Italian priest, scientist, and proud preformationist and ovist. In the 1780s, he observed the mating and reproduction of frogs. Keen to prove his theories correct, he searched for a way to show that sperm was unnecessary for reproduction. He was given the answer by a friend and colleague, Jean-Antoine Nollet. While Spallanzani is the most famous frog-dressing scientist, he was not the first. Thirty years earlier, Nollet and René Antoine Ferchault de Réaumur had conducted a similar experiment where they had put pants made of waxed taffeta on frogs.
Spallanzani seemed tickled by the idea of frog pants. In his 1789, “Dissertations Relative to the Natural History of Animals and Vegetables,” he wrote, “The idea of the breeches, however whimsical and ridiculous it may appear, did not displease me, and I resolved to put it in practice.”
So into the pants the male frogs went. They still mated with the female frogs, who still laid eggs. These unfertilized eggs, of course, failed to turn into tadpoles. Through many experiments, Spallanzani observed that sperm was a necessary ingredient to creating a tadpole. Surprisingly, this did nothing to shake his belief in ovism. He instead posited that the tadpole was already “preformed” inside the egg, and that the semen was needed to activate it.
Despite Spallanzani’s conclusions, the experiments he conducted and the data he collected were valuable in establishing sperm’s necessary role in fertilization. Contemporaries and future scientists would build off of his work as they worked to show that both the sperm and the egg contain vital instructions for creating new life through sexual reproduction. Not only that, but he put pants on frogs. And that’s just fun.
Spontaneous generation—Life can be created through a mix of organic and inorganic material.
Biogenesis—Life must come from other living things.
Preformation—Living things grow from eggs or seeds that contained tiny versions of the fully-formed being.
Epigenesis—Living things form from more than one element (such as an egg and a sperm), and will develop and change before birth.
Ovism—Preformed organisms exist inside the egg.
Spermism—Preformed organisms exist inside the sperm.