Unveiling the Mysteries of Human Procreation: Historical Perspectives and Scientific Inquiry

During the 17th and 18th centuries, a significant scientific and philosophical question centered around human procreation. Some believed the egg was the origin of life, while others asserted it was semen. Semen, when uniting with the egg, was often perceived as ethereal, described as a spirit, vapor, or odor rather than a physical substance. In 1677, Dutch microscopist Antonie van Leeuwenhoek examined semen from various species, including his own, and discovered numerous spermatozoa, though he didn't initially associate them with fertilization. By 1683, he concluded that "man originates not from an egg but from an animalcule within the male seed," noting the transfer of egg components to the spermatozoon.

During the mid-eighteenth century, Spallanzani postulated that all humans were enclosed within the initial female figure, Eve, and developed further through the impact of semen. A sculpture titled "Eve and the Serpent," created in 1913 by Belgian sculptor Albert Desenfans (1845–1938), can be found in Brussels' Josaphat Park.

Italian priest-biologist Lazzaro Spallanzani supported the preformation theory, suggesting that all living beings were created by God within the first female of their species. The individual inside the egg was pre-formed and expanded under semen's influence. In 1768, Spallanzani highlighted the importance of both the solid portion of semen and the egg in reproduction but did not recognize spermatozoa's role.

In the 1870s, two fertilization theories emerged: one proposing that spermatozoa stimulated egg development through mechanical vibrations, and the other suggesting sperm physically penetrated the egg, mixing chemical components with the yolk. In 1876, German embryologist Oscar Hertwig used transparent sea urchins to study fertilization. He microscopically observed spermatozoa entering and fusing with the egg nucleus. Hertwig also found that a single spermatozoon could fertilize an egg and that a protective membrane formed upon entry, preventing further penetration by other spermatozoa.