Sex cells: Scientists have been wrong for 350 years about how sperm swim – here’s what’s really going on

The nature of sperm was first discovered in 1677, using rudimentary microscopes, and our understanding of how they make their incredible journey to fertilize the egg hasn’t changed much since – until now.

Dutch scientist Antonie van Leeuwenhoek was the first to observe these “living animalcules,” which he observed “like eels in water,” travelling in a “snakelike movement” – something he apparently didn’t see coming. 

As all scientists know, sex cells, but our understanding of just how these tiny sperm manage to essentially scale the equivalent of Mount Everest on their bellies just by wriggling hasn’t really advanced much over the centuries.

It wasn’t until recently that a team of researchers from the UK and Mexico mathematically reconstructed the movements of a sperm’s tail in three dimensions, using state-of-the-art 3D microscopy technology. 

Even more powerful modern telescopes showed much the same thing as had been witnessed back in the 17th century – a whole lot of wriggling – so a super-fast camera was needed to capture and study the individual movements, as sperm tails whip back and forth roughly 20 times per second.

Sampling at a rate of 55,000 frames per second while oscillating up and down to scan and capture the full complexity of the movement from every angle, the researchers discovered one truly mind-blowing fact: sperm is actually lopsided and wiggles along only its dominant side.

Anyone with rudimentary swimming or canoeing experience would immediately grasp the inherent problem in lopsided propulsion: namely, that you wouldn't get very far and would be stuck turning in circles instead. 

However, it seems our smart-alec swimmers are more adept and agile than we could possibly have imagined, as they actually corkscrew to propel themselves towards the egg and life as a human, spinning their bodies as their tails rotate.  

However, when viewed using a 2D microscope, this corkscrew movement disappears and is perceived as a simple side-to-side movement, which is why we never gave the little fellas the credit they deserve.

By creating symmetry out of asymmetry, even the 50 million or so sperm that don’t make it to fertilise the egg have accomplished something in their short-lived time on this Earth. 

Sperm mobility is one identifying trait that may impact fertility, so improving our understanding of it – and the mechanism by which we all came to be alive – may help unlock the secret of fertility, especially given that over half of infertility issues occur in men. 

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