Discovery of Sperm 1678 – Parasites or Human Precursors?

In 1678, Dutch scientist Anton van Leeuwenhoek reported to the Royal Society the discovery of human spermatozoa resembling countless wormlike microscopic animals. He wrote, "What I investigated is only what remained as a residue after marital intercourse, without sinfully defiling myself. And if Your Lordship considers that these observations might disgust or disgrace the learned, I earnestly beg Your Lordship to regard them as private and to publish or destroy them as Your Lordship sees fit." Van Leeuwenhoek eventually proposed that the tiny microscopic creatures swimming in semen played a role in fertilization. Other scientists believed that sperm were merely parasites and had nothing to do with reproduction.

Around 1677, van Leeuwenhoek and his student Johan Ham used a 300-fold magnifying microscope to examine spermatozoa, which he described as animalcules (small animals). One version suggesting that the head of each sperm cell contained a tiny, fully formed human brings to mind his belief in preformation. Dutch microscopist Nicolaas Hartsoeker claimed to have seen spermatozoa in 1674, but was unsure of his observations and initially thought the wriggling cells were parasites. His famous drawing of a dwarf or tiny person squeezed into a sperm's head also suggested preformation. Hartsoeker did not claim to have seen an actual dwarf, but other researchers did! Some proposed that the dwarfs in sperm might have smaller sperm themselves, in an infinite regression of dwarfs within dwarfs. Of course, as researchers began to show how organs gradually appeared during development in creatures such as chicks, it became clear that animals were not in a nearly complete form from the outset.

The word sperm generally refers to the male reproductive cell, while spermatozoan specifically refers to a motile sperm cell with an attached, whiplike tail. Today we know that, in humans, the sperm cell has 23 chromosomes (threadlike carriers of genetic information) that combine with the 23 chromosomes in the female egg when fertilization occurs.

Description of the Article Image:

1. Sperm surrounding an egg just before fertilization.
2. A drawing of a sperm highlighting the head, the whiplike tail and the midpiece containing a filamentous nucleus and many energy-producing mitochondria for tail movement and propulsion.

Historical Figures Mentioned in the Article: Anton Philips van Leeuwenhoek (1632–1723), Nicolaas Hartsoeker (1656–1725)

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