Sperm do not swim, they spin

Sperm obviously play a vital role in the fertilisation of almost every living organism on the planet. They have long tails called flagella that help to propel the little swimmers up through the reproductive tract to the egg, however recent research has shown that the way we originally thought the sperm swim, is in fact incorrect.

A single sperm needs to travel on average approximately 10cm to reach the egg, which is equivalent to a human walking from Sydney to Perth and back again. The scientist who discovered sperm did so after he developed his own microscope out of molten glass in the 17th century and described them as a “living animalcule” that had a “tail, which, when swimming, lashes with a snakelike movement, like eels in water”. To this day, scientists have believed sperm are propelled forward by whipping their tails back and forth, however what we believe we are witnessing is simply an optical illusion.

By using state-of-the-art 3D technology, researchers from the United Kingdom and Mexico were able to construct the tail of a sperm. The sperm’s tail or flagella is so fast, it is capable of beating over 20 swimming strokes in less than a second. Scientists needed a camera fast enough to capture this high-speed movement, and break it down frame by frame, and what they discovered was that the sperm’s tail in in fact skewed and will only wiggle on one side.

In order for the sperm to adapt and not simply swim around in circles, they roll as they swim, similar to the way otters will move in a corkscrew movement through the water. The way the sperm rolls gives off the optical illusion that its tail has a side-to-side movement, however this new development has revealed that in order to correct their lop-sidedness, the sperm will essentially “drill” their way through the fluid as they move towards the egg.

By understanding more about the structure of the sperm, scientists can use this information to help develop more advanced diagnostic tools for identifying unhealthy sperm and helping to improve fertility.