Sciences Participating with Arts & Culture in Education

Fertilization Miss-Understood

Is the sperm truly a strong swimmer and powerful penetrator? Is the egg really a Damsel in Distress, a Sleeping Beauty, waiting to be activated and fertilized? Although it prides itself on its objectivity, there is an inherent gender bias in the sciences that influences the way research is conducted and interpreted. In particular, the passive-female and active-male stereotypes are embedded into the classic view of fertilization, and persists even in light of new evidence.

The earliest recorded scientific model of fertilization was developed by Aristotle (384-322 BCE). He argued that male ejaculate is the “seed” that implants itself into the menstrual “soil” of the female. He even described this “seed” generated by the male as containing the fetus itself: “By definition the male is that which is able to generate another…the female is that which is able to generate in itself and out of which comes into being the offspring previously existing in the generator” (Tuana). Aristotle also likened the process to a craftsman carving from a piece of wood, where the female provides the “raw material”, and the male “determines the function of the object to be produced and gives it its form” (Tuana). Incidentally, Aristotle’s reasoning had many inconsistencies, which only highlights the persistence of his underlying gender bias. These underlying assumptions are made clear when he states: “But the female, as female, is passive, and the male, as male, is active, and the principle of movement comes from him” (Tuana). This implies that females are passive and males are active by their very nature, and thus their contributions to conception follow accordingly.

Throughout history, the notion of female passivity has imbedded itself into the scientific model of fertilization. The same paradigm is propagated in the textbooks and research journals of the 20th century. The egg is described in passive terms: “eggs are “released”, or “shed” from the ovary […] until a sperm “penetrates” and “activates” them” (Tobach). Textbooks describe how “the egg is seen as large and passive. It does not move or journey, but passively “is transported”, “is swept”, or even “drifts” along the fallopian tube” (Martin). Despite growing evidence to the contrary, the passive female stereotype persists in our description of fertilization. The gender bias is often hidden in the language, even if the authors explicitly discuss the egg’s active role. In one article, the authors begin by saying “recent research suggests the almost heretical view that sperm and egg are mutually active partners” (Schatten). However, they later compare the egg to Sleeping Beauty: “[the egg] leaps from sleep to hubbub […] whose metabolic fires leap up and blaze at its fateful meeting with the sperm” (Schatten). Using this metaphor, the egg assumes the passive role of Sleeping Beauty, waiting for the Prince Charming sperm, even when the authors stated that the egg and sperm are mutually active partners! In such examples, the same traditional model is used even when it does not reflect the evidence, which goes to show how deeply rooted these biases are.

Results that challenge the notion of the active-male and passive-female face greater resistance before being accepted into the standard description of fertilization. In the 1983 edition of Developmental Biology (Gilbert), the sperm is said to be “able to travel long distances by whipping its flagellum”. Other textbooks use similar language to describe the sperm’s movement: “Their tails are ‘strong’ and efficiently powered. Together with the forces of ejaculation, they can ‘propel the semen into the deepest recesses of the vagina’” (Martin). The traditional model states that the sperm moves through the female system due to its own strength and speed. However, studies have shown that in fact the opposite is true: the female system moves the sperm: “The translocation of sperm from the vagina to the oviduct involves many processes that work at different times and places […] sperm motility (i.e. flagellar action) is probably a minor factor in getting the sperm to the oviduct […] rather, sperm appear to be translocated to the oviduct by the muscular activity of the uterus” (Schiebinger). The female reproductive system even brings the sperm to where fertilization is most likely: “the uterus and fallopian tubes of a woman will actively transport sperm to the dominant follicle” (Schiebinger). Although the female’s active role in sperm transport was well-documented since the 1930s, textbooks published 50 years later were still describing the sperm as self-propelled, with little to no mention of the female’s significant role in sperm motility.

Often the researchers who find evidence for female activity are prone to maintaining the passive stereotype in their interpretations and descriptions. In the traditional model, the egg passively waits for the sperm’s arrival, and the sperm breaks through the egg’s protective coat (the zona pellucida) as a result of its own strength and speed: “It was thought that the zona […] formed an impenetrable barrier. Sperm overcame the barrier by mechanically burrowing through, thrashing their tails and […] released digestive enzymes that chemically broke down the zona” (Martin). However, a recent study shows that sperm are actually weak swimmers. The study showed that the sperm’s “heads trashed from side to side ten times more vigorously than their bodies pushed forward (Freedman). As a result, rather than forcefully overcoming the egg’s barrier, “the flagellum produces forces on the head which act in directions tending to pull the sperm away from the zona” (Baltz). The results show that sperm are more prone to escaping the egg than penetrating it, when considering the sperm alone. In order for fertilization to be possible, the egg plays an active role by holding the sperm’s head in place on the zona. The egg’s role does not end there: certain bonds must be broken and formed at the right time for the sperm to successfully make it through the zona. The study suggests “that penetration of the zona pellucida by mammalian sperm must result from a highly organized and regulated sequence of events rather than being an inevitable result of the simple adhesion of a sperm with a beating flagellum to the zona” (Baltz). It is not possible for the sperm to bind to the egg and swim into it: the sperm can only cross the zona only when both sperm and egg are actively involved. The new findings show that the egg plays an equally active (and essential) role in bringing the sperm through the zona, yet this new evidence was resisted at first: “Not until August 1987, more than three years after the findings […] did these researchers reconceptualise the process to give the egg a more active role” (Martin). In the revised edition, the researchers refer to the interactive nature of the process: “sperm-zona bonds must capture the sperm”. However, they continue to attribute the process to the sperm’s activity alone: “Before reaching the egg plasma membrane, a sperm must first bind to the zona, reorient towards the egg, and penetrate the zona”. Even after these discoveries, it is difficult to abandon the active sperm and passive egg imagery.