Without the benefit of modern science, folks in the Dark Ages had some decidedly peculiar beliefs about the world they lived in. In fact, things went backwards after the collapse of the Roman Empire, and much knowledge was lost for centuries. In the Dark Ages, superstition and misconception ruled the roost in all kinds of bizarre ways.
Preformationism was the entirely mistaken theory that humans were perfectly formed in miniature in sperm. Once the sperm had been deposited into the womb, all that was required was for the tiny human to grow to the right size to be born. In fact, it was believed that all living beings were created in this way and in their tiny forms these were known as homunculi.