Spermism

Spermism was one of two models of preformationism, a theory of embryo generation prevalent in the late seventeenth through the end of the eighteenth century. Spermist preformationism was the belief that offspring develop from a tiny fully-formed embryo contained within the head of a sperm cell. This model developed slightly later than the opposing ovist model because sperm cells were not seen under the microscope until about 1677. Spermism was never as dominant as ovist preformationism, but it had ardent followers whose work and writings greatly influenced the development of embryology in this time period. Spermism was and is now sometimes referred to as animalculism, a name taken from the term most naturalists at the time used to refer to microscopic organisms, or vermiculism, which comes from a specific term for sperm cells referring to their worm-like appearance. The most notable spermist philosophers and scientists were Nicolaas Hartsoeker, Anton Leeuwenhoek, and Wilhelm Gottfried Liebniz.

The discovery of sperm in animal semen was the result of improvements in the microscope in the middle part of the seventeenth century. Many of these improvements were the work of Anton Leeuwenhoek, a Dutch lens grinder and optics manufacturer. The Royal Society of London officially credited Leeuwenhoek and his student Johan Ham with the discovery of sperm cells (then called seminal animalcules) in 1677. Nicolaas Hartsoeker, a young Dutch microscopist, disputed this claim, saying he had first seen them under the microscope in 1674 but was not certain enough about what he had seen to make his results known at the time; Hartsoeker had assumed at first that the tiny wriggling cells were a type of parasite. Already familiar with the theory of preformationism, Hartsoeker, Leeuwenhoek, and others began to investigate the sperm cells for signs that they could be the carrier of the preformed offspring instead of the ovum.

The scientists conducting this research based most of their positive conclusions on the appearance of sperm under the microscope. Hartsoeker is famous for a sketch of a homunculus in the head of a human sperm, which he published in 1694 in his Essai de Dioptriques, though Hartsoeker does not claim to have actually seen this preformed human under the microscope. Other researchers, such as Dalenpatius (pseudonym of Francois de Plantade) in 1679, and Nicolas Andry in 1700, did state that they had seen not only small humans in the sperm cells, but had seen that the sperm cells of each species they studied resembled the adults of the species. Albrecht von Haller, a well-respected contemporary microscopist and an adherent to the opposing ovist model, wrote that he had looked for this evidence in semen, but had not found it.

Besides the lack of clear evidence, one of the main problems with the spermist model was the implied wastefulness of human lives or human souls. If each human sperm cell contained a potential person, critics pointed out, then millions of people were dying with each successful conception. This was enough to make many preformationists reject spermism in favor of ovism, because ovism did not seem to carry with it that same degree of wastefulness. Leeuwenhoek and Hartsoeker tried to explain this resulting waste by pointing to the wastefulness of seeds in plants and of eggs in frogs. When this failed to satisfy the opponents of spermism, Hartsoeker formulated the idea that is now called panspermism: sperm that did not find purchase in a female’s womb evaporated into the air and became particles that floated until they could be recycled into active sperm. This idea was also propounded by Wilhelm Gottfried Liebniz, the philosopher-mathematician and co-inventor of calculus, who tied it into his metaphysical theory of monadism. While this idea addressed the problem of wastefulness, it introduced even more difficulties for the spermists, who now had to deal with explaining the process by which these floating sperm cells with their preformed embryos could find their way back to the male animals of their species. Accordingly, panspermism did not gain much purchase. James Cooke reintroduced the idea in 1762, and his writings were satirized by Sir John Hill in a paper called Lucine sine Concubita, detailing a machine invented to capture floating sperm cells.

The idea of panspermism thus failed to resolve the problem of wastefulness. Spermists in the 18th century turned to very different explanations. Jacques Fabien Gautier d’Agoty claimed that rather than each sperm containing a single fully formed embryo, there is only one embryo contained in each discharge of semen, whose parts are present in the semen but spread out. A talented anatomical illustrator, Gautier produced a plate of a miniature horse he had seen in horse semen, and in 1750 published an illustration of the preformed human embryo that he said could be seen in semen discharged into water in a glass. In 1765, Jean Astruc wrote in defense of spermism, saying that it was the only way to explain heredity. Astruc also described the homunculus present in sperm as having no soul until the sperm cell unites with the egg. This solved neatly the problem of wastefulness, but invoked the competing theory of epigenesis by making both the sperm and the egg required for fertilization.

The brief popularity of spermism marks an important episode in science history. Spermism never attracted as many adherents as ovist preformationism because of its problems with the implied wastefulness of God or Nature, and because no clear evidence could be found that a preformed embryo did exist within sperm cells. However, the spermists’ work investigating the nature and function of sperm cells was instrumental in the progression of embryology.