Experts: It is not true that sperm swim in the journey of conception Most of us have learned about the process of human fertilization as if ...

Experts: It is not true that sperm swim in the journey of conception

Most of us have learned about the process of human fertilization as if it were a story.

The story goes that millions of tadpoles with big heads and thin tails swim happily in the environment with one goal: to reach the egg that awaits their arrival.

The fastest and lightest seed that manages to complete this marathon wins the prize.

It defeats the egg, penetrates into it, and thus the embryo begins to take shape.

Whether there are more words than these or less, this is a narrative that usually accompanies the process of conception.

However, this story that presents the sperm as the perfect agent in opposition to the egg, whose role is considered passive, does not accurately depict how this event occurs.

Both—and especially a woman's reproductive tract—play an important role in reproduction.

'Checkpoints'

This narrative begins with ejaculation.

Once produced, tens of millions of sperm are deposited in the vagina (it is estimated that the average ejaculate may contain around 250 million sperm).

Once there, they must first overcome the cervical barrier, Kristin Hook, an evolutionary biologist from the science, technology assessment and analysis team of the US Government Accountability Office, explains to BBC Mundo.

"Inside the reproductive tract there is a series of what I would call, from a female point of view, 'checkpoints' that sperm must pass through to reach the fertilization site, which is far from the point of entry."

Unless the seeds are in good condition (many have DNA damage or other defects), they will not be able to pass this barrier.

''This is a very important selection process,'' says Daniel Brison, scientific director of the Department of Obstetrics and Gynecology at the University of Manchester in England.

"Of the several million sperm that are released by ejaculation, only a few hundred will reach the egg."

Vibrant and fluid

However, sperm cannot reach the end of the fallopian tube alone, where pregnancy occurs, because they are not strong enough.

The movement that the sperm makes in the lateral parts is ten times stronger than that which it makes in the front.

"Sperm don't swim, but they're pushed more by uterine contractions," explains Brison.

"Swimming is only a small part and that only happens when the sperm reaches the egg," adds the researcher.

On the other hand, the fluid inside the uterus and fallopian tubes can also change the path of the sperm, promote or prevent their movement, change their position.

In short, it is the stage of the fallopian tube, as well as the ongoing process - whether it contains salty or thick sticky water, or a certain type of acid ie pH - all are controlled by the female reproductive system, which will control how pregnancy will occur.

That is to say: which sperm will be allowed to meet the reproductive egg'', Virgina Hayssen, professor of Biology at Smith College in the United States, told BBC Mundo.

"The pH or acidity of the vaginal environment is lower than it is suitable for sperm, but this acid is necessary (...) for a series of changes to occur in the membrane and digestion of sperm, which will allow them to have more mobility, faster metabolism, and also the ability to penetrate the outer protein layer of the oocyte (immature egg), which is very difficult to penetrate," explains Filippo Zambelli, a researcher at the Eugin Group in Spain, which deals with assisted reproduction.

Some researchers maintain that a woman's climax can also contribute to this journey of sperm by causing muscle contractions, but others insist that more studies are needed to confirm this theory.

A short trip to the egg

The egg, meanwhile, doesn't just wait for the sperm to arrive.

Although the egg does not have the ability to move on its own, cilia (a type of hair) inside the tube help it move down the short journey from the womb.

"The egg moves through the fallopian tube towards the uterus, releasing chemical molecules into the fluid that attract the sperm and guide them towards it," says Zambelli.

The egg can use these molecules to ''pull or repel, as well as adjust where each sperm goes,'' Hayssen concludes.

Describing the encounter between sperm and egg as an act of penetration also does not accurately reflect what happens, since the egg is the one that attracts the sperm and controls—in most cases—that one sperm connects.

The association is actually a process of mutual interaction in which both parties take an active role and in which a series of receptors and chemical substances are involved.

Difficult environment

Is the environment in which sperm grow hostile, as they say?

According to Hayssen, this ten ani is another because it describes the event from a male point of view.

"It is hostility if you consider it as competition and not cooperation," he says.

"The environment promotes a generation of children who can live, so it is not hostile to the goal, which at the end of the day, the child is found."

Photo: ''The environment is trying to produce the best child, which can empower many children, so the environment cannot be hostile.

If you look at it from a female point of view, the uterus does what needs to be done to benefit the mother in having better children.

New technology, old ideas

Although some details of the conception process have recently become known due to advancing scientific research, much of the information, such as the limited importance of sperm motility, has been known for decades.

The American anthropologist Emily Martin was one of the first people to focus on the language used to talk about fertilization, and to see how cultural values ​​in general enter into the way scientists describe their discoveries about the real world.

Her academic writings - published in the early 1990s - which analyze in detail the gender stereotypes hidden in the scientific literature on the subject, became part of the reference for the issue of gender equality.

The experts who spoke to BBC Mundo also mention the lack of representation of women in science and also in decision-making areas in education.

"The continued lack of representation in science of people with different perspectives will affect the kind of questions you ask and the information you get," says Kristin Hook.

Hayssen emphasizes the need to question the terms we use and use neutral language: we should use "pregnancy and not fertilization", for example.

But eliminating gender bias in our understanding of the process of conception is not only necessary to correct scientific misinformation and accurately describe biological processes.

It is also a fundamental step in improving existing assisted reproductive treatments and making way for new technologies.