Sperm don’t swim anything like we thought they did, new study finds

Under a microscope, human sperm seem to swim like wiggling eels, tails gyrating to and fro as they seek an egg to fertilize. 

But now, new 3D microscopy and high-speed video reveal that sperm don’t swim in this simple, symmetrical motion at all. Instead, they move with a rollicking spin that compensates for the fact that their tails actually beat only to one side. 

“It’s almost like if you’re a swimmer, but you could only wiggle your leg to one side,” said study author Hermes Gadêlha, a mathematician at the University of Bristol in the U.K. “If you did this in a swimming pool and you only did this to one side, you would always swim in circles. … Nature in its wisdom came [up] with a very complex, ingenious way to go forward.” 

Strange swimmers

The first person to observe human sperm close up was Antonie van Leeuwenhoek, a Dutch scientist known as the father of microbiology. In 1677, van Leeuwenhoek turned his newly developed microscope toward his own semen, seeing for the first time that the fluid was filled with tiny, wiggling cells. 

Under a 2D microscope, it was clear that the sperm were propelled by tails, which seemed to wiggle side-to-side as the sperm head rotated. For the next 343 years, this was the understanding of how human sperm moved. 

“[M]any scientists have postulated that there is likely to be a very important 3D element to how the sperm tail moves, but to date we have not had the technology to reliably make such measurements,” said Allan Pacey, a professor of andrology at the University of Sheffield in England, who was not involved in the research. 

The new research is thus a “significant step forward,” Pacey wrote in an email to Live Science. 

Gadêlha and his colleagues at the Universidad Nacional Autónoma de México started the research out of “blue-sky exploration,” Gadêlha said. Using microscopy techniques that allow for imaging in three dimensions and a high-speed camera that can capture 55,000 frames per second, they recorded human sperm swimming on a microscope slide. 

“What we found was something utterly surprising, because it completely broke with our belief system,” Gadêlha told Live Science. 

The sperm tails weren’t wiggling, whip-like, side-to-side. Instead, they could only beat in one direction. In order to wring forward motion out of this asymmetrical tail movement, the sperm head rotated with a jittery motion at the same time that the tail rotated.The head rotation and the tail are actually two separate movements controlled by two different cellular mechanisms, Gadêlha said. But when they combine, the result is something like a spinning otter or a rotating drill bit. Over the course of a 360-degree rotation, the one-side tail movement evens out, adding up to forward propulsion.

“The sperm is not even swimming, the sperm is drilling into the fluid,” Gadêlha said. 

The researchers published their findings today (July 31) in the journal Science Advances.

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Asymmetry and fertility

In technical terms, how the sperm moves is called precession, meaning it rotates around an axis, but that axis of rotation is changing. The planets do this in their rotational journeys around the sun, but a more familiar example might be a spinning top, which wobbles and dances about the floor as it rotates on its tip. 

“It’s important to note that on their journey to the egg that sperm will swim through a much more complex environment than the drop of fluid in which they were observed for this study,” Pacey said. “In the woman’s body, they will have to swim in narrow channels of very sticky fluid in the cervix, walls of undulating cells in the fallopian tubes, as well have to cope with muscular contractions and fluid being pushed along (by the wafting tops of cells called cilia) in the opposite direction to where they want to go. However, if they are indeed able to drill their way forward, I can now see in much better clarity how sperm might cope with this assault course in order to reach the egg and be able to get inside it,” Pacey said

Sperm motility, or ability to move, is one of the key metrics fertility doctors look at when assessing male fertility, Gadêlha said. The rolling of the sperm’s head isn’t currently considered in any of these metrics, but it’s possible that further study could reveal certain defects that disrupt this rotation, and thus stymy the sperm’s movement. 

Fertility clinics use 2D microscopy, and more work is needed to find out if 3D microscopy could benefit their analysis, Pacey said. 

“Certainly, any 3D approach would have to be quick, cheap and automated to have any clinical value,” he said. “But regardless of this, this paper is certainly a step in the right direction.”

Originally published in Live Science.

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These Baby High Chairs Will Give Them the Safe Boost They Need

Aside from diapers and baby formula, the other constant in your life as a parent of a baby is going to be a reliable baby high chair. Whether you’re eating at home, at a relative’s, or at a restaurant, you’re going to need something to give them a boost while keeping them safely contained so you can eat too. The best baby high chairs come in a variety of shapes, sizes, and colors that you can match to their favorite outfits or colors. Many high chairs come with different features, so it’s important to consider what’s the best option for you and your little one.

When you’re picking out a baby high chair, you’ll first want to determine where you’re going to use it most. If you’re looking for a travel-friendly version, you’ll want a compact one that’s easy to fit in the car. To avoid buying high chairs as they grow out of them, one that easily adjusts as they grow up is a must. Some high chairs even convert into a step stool, so that’s another smart thing to consider. Ahead, we’ve rounded up the best baby high chairs to meet your needs.

1. Infantino High Chair

They (and you) won’t be able to resist this darling fox baby high chair. This four-in-one baby high chair is also smart too by saving space in your home. It converts from a booster into a toddler chair with ease so it will grow with them as they outgrow their baby high chair. It’s also easy to clean and has an easy release food tray for fuss-free cleaning. You can wipe down the soft cushioning without a problem, too. With front wheels, you can reposition the chair to face however you’d like.

2. Graco Everystep High Chair

If you want a baby high chair that does more than let your little one safely sit, then this convertible option will meet your needs. This smart high chair easily converts from a high chair to a kids step stool for when they need to reach for the counter. With seven total growing stages, you can keep this high chair for years without having to replace it as they get bigger. It’s narrowed down to three stages: the infant high chair with three reclining positions, fully featured baby high chair with seven height positions and dishwasher-safe tray insert, and infant booster seat that brings them right up to the table by attaching to the table.

3. Fisher Price SpaceSaver High Chair

Whether you have tight quarters at home or travel often with baby, this compact baby high chair is going to save a ton of valuable space wherever you go. Not to mention, it has a stylish neutral design that will look great in your home. It may be smaller, but it still packs in all the features of a full size high chair. It even transforms from an infant booster to a toddler one too, so you don’t have to purchase a new one as they get older. There’s two height adjustments and three recline positions for ultimate comfort, and the machine-washable seat pad makes clean ups a breeze. The deep-dish tray prevents food from falling over the edge, too.


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