spermists

Spermists were proponents of preformationism in embryology who argued that the male sex cell (the sperm) contains a fully formed miniature human, or homunculus, which develops into a complete individual after fertilization. In this view, the female’s role is largely to provide nutrition and a suitable environment for growth, while the paternal germ cell supplies the preformed organism.

The opposing school, the ovists, held that the egg contains the preformed embryo and that fertilization merely activates its development. The dispute was part of the broader 17th–18th century preformation debate that arose with improvements in microscopy and observations of reproduction. The idea reflected broader questions about where life begins and how development proceeds.

Notable proponents of spermism included Nicolaas Hartsoeker, whose 1695 engraving popularized the image of a homunculus dwelling inside a sperm. Other contemporaries argued for paternal preformation or variations of preformation, while critics pointed to the egg’s demonstrated role and to emerging ideas of epigenesis, which posited development from undifferentiated tissue rather than from a preformed miniature.

By the 18th and 19th centuries, accumulating embryological evidence—along with advances in genetics and a growing understanding of fertilization and development—undermined the preformation theory. Spermism faded as a scientific position, giving way to modern explanations of development that emphasize progressive differentiation after fertilization. Today, the term is used mainly in historical discussions of early theories of reproduction.