Turns out - we’ve been wrong about how sperm move for over 350 years. Yep, we’re talking sperm this week - saddle up.
In the late 1600s, Antonie van Leeuwenhoek, a Dutch microbiologist, was the first to discover sperm by viewing it through a microscope that he had built. Considered the “Father of Microbiology”, he made several crucial microscopic discoveries including blood cells and bacteria. He also made over 500 different types of microscopes - each crafted to study and view specific objects.
After studying various microorganisms, his science-bros tried to convince him to put his own semen under the lens. Van Leeuwenhoek demurely declined for a time, but finally gave in to the science-peer-pressure. What he saw baffled him at first - tiny little swimmers he dubbed animalcules. He was hesitant to publish his findings, but after studying the animalcules more, van Leeuwenhoek wrote to the Royal Society of London in 1677 detailing his discovery. “If your Lordship should consider that these observations may disgust or scandalise the learned, I earnestly beg your Lordship to regard them as private and to publish or destroy them as your Lordship sees fit.” The Lordship was fascinated and the findings were published in the journal Philosophical Transactionsin 1678 - kickstarting a wave of sperm biology studies.
Finding these tiny swimmers in semen was fairly shocking for the era, especially considering scientists (let alone the general populace) did not yet fully understand how babies were made. There were many theories floating around, such as the idea that men made the babies and then passed them to women to incubate and deliver (cool cool). Or that a sort of vapor was emitted when men ejaculated and this in turn stimulated the woman to make a baby. And of course the ever popular stork delivery concept.
In subsequent sperm-studies, scientists devised a hypothesis of how the sperm moved and swam. They observed that the sperm wiggled their tails side to side in a sort of whip-like motion in order to propel themselves forward. This hypothesis held for over 350 years, until researchers from the University of Bristol and Universidad Nacional Autonoma de Mexico decided it was time to employ advanced 3D microscopy technology and take another look.
In a carefully designed study, scientists used a camera that captured the sperms’ movement at 55,000 frames per second. These photos were then used to create a mathematical formula and 3D model of the swimming patterns. What they found was that sperm are lop-sided. Yes, lop-sided! They only wiggle their tails in one direction performing one-sided strokes. In order to counteract this and avoid swimming in circles they use an opposing force - spinning their heads like a top - to create forward momentum, similar to the movement a drill makes.
Previous to this, scientists had only been able to utilize the 2D technology available to them, and these microscopes were not able to pick up the lop-sided characteristic. Instead, the images reflected back to the viewer created an illusion of symmetry - thus leading to the original hypothesis which stood untested for hundreds of years.