We all learned the same story in our childhood. To create an embryo, spermatozoa embark on a frantic race. Only the strongest and fastest succeeds in fertilizing the egg… which is passively waiting. An image of reproduction that is false and tinged with gender stereotypes. No, the egg is not just waiting for its valiant knight to honor its existence, biology recognizes today.
Fertilization is rather the result of an interaction — of prodigious refinement — between the ovum and the sperm. “We make the sperm the hero of fertilization, while a lot of research shows that there is an active process, argues Stéphanie Pache, professor of sociology of gender and sexualities at UQAM. The egg selects the sperm it lets in. »
The idea, well anchored in our minds, that male gametes do all the work is certainly a hundred leagues from reality, agrees the Dr Pierre Leclerc, professor in the Department of Obstetrics and Gynecology at Université Laval.
“From a strictly dynamic point of view, it’s true that the sperm move more. It moves, while the egg remains in place, recognizes the specialist in human reproduction. But he can’t do it all on his own. The egg has a large job of selection to be made. »
A work of incredible complexity. And by which several protective barriers erected on the course of the spermatozoa make it possible to select the one – the key – which will be able to fit into the lock – the ovum, explains the Dr Leclerc.
The last word
Contrary to popular belief, it is not millions of sperm that will face the egg at the end of the process, but rather one or two. After ejaculation, many spermatozoa are blocked as soon as they arrive in the cervix, then further to the border between the uterus and the fallopian tubes, underlines the expert. “Thereafter, in the fallopian tubes, the sperm will remain attached to the cells and will be released almost one by one to travel to the fertilization site closer to the ovary,” he says.
There, the cumulus (composed of cells linked together by a viscous and sticky fluid) will in turn block the sperm less able to fertilize the egg, continues the doctor. The zona pellucida that envelops the ovum will carry out another stage of selection. Only sperm belonging to the human species and those with hyperactive motility (the movements of the flagellum are stronger and more vigorous) will be able to cross the barrier, explains the Dr Leclerc.
The sperm will then come into contact with the membrane of the egg, to stick to it and ultimately fuse with it. “This is where sperm motility automatically stops,” says the expert. It is the egg that will do the work to make the sperm penetrate and make sure that it rushes inside the oocyte. »
To achieve this, proteins on the surface of the egg will ensure that complementary proteins are on the surface of the sperm. “It is the egg that has the last word, supports the Dr Leclerc. It is he who will decide who passes and who does not pass. »
gender norms
We are therefore far from this mirage that the male component does all the work while its female counterpart waits. A myth that is however tenacious, despite advances in biology.
However, in 1991, the American anthropologist Emily Martin, of Johns Hopkins University, established, in a significant article entitled The Egg and the Sperm: How Science Has Constructed a Romance Based on Stereotypical Male-Female Roles, how “stereotypes central to our cultural definition of male and female” have colored the representation of the fertilization process not only in the popular imagination, but also in biology books.
While the sperm are depicted as “survivors”, “strong and energetic”, enlisted in a “perilous mission” which will crown a big winner, the egg is compared to “a sleeping wife who awaits the magic kiss of her companion which will instill life in her, she cites among other examples.
This reading of biology, giving the beautiful role to the male sex, is not unique to our time, but dates back several centuries, notes Julie Lavigne, art historian and professor in the Department of Sexology at UQAM. There was probably a desire on the part of man to regain power over the gestation process, from which he is completely excluded, notes the expert in ethics and representation of sexuality.
And this desire, asserted from the 18thand century, to document the differences between men and women. “It just made sense, since the woman [était perçue] as weaker and that her egg is not moving, that it was waiting to be fertilized by the valiant sperm”, mentions the professor. In biology, as in other sciences, the representations that we have of reality can be “tinted by generally conveyed social norms, including gender norms”, underlines Stéphanie Pache, professor of sociology of gender and sexualities at UQAM.
Should we understand that biology is political? Certainly, say the two researchers. “The challenge is that we don’t have direct access to reality,” notes Stéphanie Pache. You can take a photo using, among other things, electron microscopy, and the photo is real. But the way we will understand the photo and describe it, it will be mediated by our language and the way we see the world. »
New biomedical technologies, the feminization of the scientific professions and the acceptance of a more egalitarian role for women in society have, over time, widened the field of possibilities. But there still remains to be deconstructed the fictionalized stories that have fertilized the collective imagination.