20 Insane Scientific Theories That People Actually Believed

A tiny person inside a sperm, as drawn by Nicolaas Hartsoeker (c. 1695). Wikimedia Commons.

20. The dominant scientific theory throughout Renaissance Europe, preformism held that humans existed in miniature but complete forms in male sperm and were subsequently enlarged via the female womb

Believed to have originated from Ancient Greece, with Pythagoras credited as one of the earliest individuals to advance the notion, “spermism” dictated the father contributed the essential characteristics of a human offspring whilst the mother merely provided an oven in which the child grew. Transmitted into European scientific understanding by Aristotle, and subsequently elaborated by Galen, it was not until the 17th century the belief started to face testing scrutiny. However, the core issue of how unorganized matter could transform into organized life – known today as epigenesis – remained a vexing question for scientists of the past, resulting in a stunning conclusion being reached.

In contrast to the modern scientific understanding of embryonic development, naturalists claimed instead humans must exist in a miniature preformed state. Developed into a widespread theory by Antonie van Leeuwenhoek, the Dutch scientist determined “in no full-grown body are there any vessels which may not be found likewise in semen”. Producing the theory of “preformation”, Leeuwenhoek reasoned human sperm comprised tiny but nonetheless complete humans which were transmitted into the womb for incubation. Remaining the dominant theory of generation during the 18th century, it was not until Dalton’s atomic theory of matter that preformation was dealt a decisive blow in the early 19th century.