Scientists Have Figured Out Why Sperm Bends

"The tail is something more intelligent than what it was believed to be."


Sperm wriggles like no other organism. When its head pushes one way, the tail moves the other way, and yet it just keeps swimming.

But how and why does sperm move the way it does?

Hermes Gadȇlha at the University of York has committed his work to unraveling this bendy mystery. He’s a mathematical biologist and the author of a new study published Wednesday in the Journal of the Royal Society Interface that tackles the biomechanics of sperm bendiness.

“The holy grail of this area is to understand how sperm can coordinate … its motion,” Gadȇlha told Inverse over Skype from his office in England, where he sat in front of a filing cabinet lacquered with (scientific) images of sperm. “We have too many question marks around.”

Researchers have been looking at the bendiness of sperm since the 1960s, with some answers only emerging within the past decade. In 2009, for example, some of the first modern lab experiments on sperm tails were conducted. To the surprise of many scientists, the research showed that sperm wiggle in a peculiar, specific way, formally dubbing it the “counterbend phenomenon.”

Earlier research also showed how the bend comes about: Sperm are full of elastic springs, sort of like cylinders firing in an engine, that maintain its shape and help it move. The springs are bundled so tight where the head and tail connect that when the tail moves, it’s forced to bend against the body, creating that signature backsliding wiggle.

But what if there was more to the wiggle?

In this latest research, Gadȇlha and his colleagues reproduced some of this data by wiggling virtual sperm and watching the counterbend as it happened. But they also took these observations a step further than anyone previously had, by building a mathematical model to help unpack how exactly sperm does its thing.

This is a real scientific illustration of real science done by real scientist. What a time to be alive. 

Ishimoto, Gadelha, Gaffney, Smith and Kirkman-Brown

Gadȇlha and his colleagues discovered that the bundle of springs isn’t just necessary to hold the sperm together physically — it also allows for information to be shared across its tiny body.

“The tail is something more intelligent than what it was believed to be,” Gadȇlha says. He compares what’s going on in a sperm’s tail to a bunch of blindfolded rowers. Even though they can’t see each other, they can work together to move forward simply by feeling the motions of the boat. The different motors in the sperm can, in this way, coordinate their motion, and hopefully inseminate that egg and win the reproductive games.

Sure, that’s cool, but Gadȇlha’s got a larger mission to change the world. Many other organisms have similar tails that need to be understood, he says, and he hopes to use this research to combat disease and improve the fertility of animals and humans. He’s particularly interested in the parasite trypanosoma, which causes truly terrifying diseases like sleeping sickness and Chaga’s disease in his native Brazil and around the world.

Trypanosoma has a tail like sperm’s, but trypanosoma move backwards. Gadȇlha wants to unpack how the same physical structure can create different movements so that we can enhance essential procedures like artificial insemination in livestock or endangered species and combat awful things like the spread of deadly diseases.

Gadȇlha also thinks understanding sperm and other small organisms will help us build better miniature robots, which are being developed in labs around the world to one day serve as alternatives to invasive surgical procedures or even as artificial replacements for cells.

It all goes to show, there’s a lot of exciting work ahead on the long and winding road of sperm tail science.

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