New Theory on How The Aggressive Egg Attracts Sperm

When it comes to describing fertilization, biologists have got it all wrong. The egg is no passive lady-in-waiting

By David H. FreedmanMay 31, 1992 7:00 PM


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Ah, fertilization--that miraculous process to which we all owe our existence. Let’s review: First, a wastefully huge swarm of sperm weakly flops along, its members bumping into walls and flailing aimlessly through thick strands of mucus. Eventually, through sheer odds of pinball-like bouncing more than anything else, a few sperm end up close to an egg. As they mill around, the egg selects one and reels it in, pinning it down in spite of its efforts to escape. It’s no contest, really. The gigantic, hardy egg yanks this tiny sperm inside, distills out the chromosomes, and sets out to become an embryo.  Or would you have put it differently? Until very recently, so would most biologists. For decades they’ve been portraying sperm as intrepid warriors battling their way to an aging, passive egg that can do little but await the sturdy victor’s final, bold plunge. But the first description is closer to the truth, insists Emily Martin, a 47-year-old researcher at Johns Hopkins who has spent the past seven years examining the metaphors used to describe fertilization. Martin is not a biologist; she’s a cultural anthropologist. But her efforts to spotlight the male- skewed imagery that permeates our views of reproduction have placed her at the center of a growing debate about how cultural myths can turn into scientific myths, and vice versa.  Martin didn’t set out to skewer biologists. Actually she was studying biology, among other things, at the University of Michigan in 1965 when a course on Japanese music hooked her on investigating other cultures. After picking up a Ph.D. in cultural anthropology from Cornell in 1971, she spent nine years traveling back and forth between the United States, Taiwan, and China, where she was studying Chinese rituals and social organization. Then, having done the study of a foreign culture that’s traditionally expected of anthropologists, and being pregnant with her first child, she started casting about for a new project closer to home. Studying your own culture is harder, she says, because everything seems so normal to you.  Not until 1982, while attending a class for expectant parents before the birth of her second child, did Martin stumble on her topic. It suddenly hit me that the way everyone was talking about their bodies was really weird, she recalls. It was the body, the uterus, and the contraction--as if these things weren’t a part of us. I realized that medical science was in need of some sort of interpretation, and my wedge would be reproductive issues. Martin started off by interviewing dozens of women on their feelings about every aspect of reproduction, from menstruation to menopause. Her book The Woman in the Body, published in 1987, explored the relation between images of the body and ideas about oneself. But by 1985 Martin realized that she had been looking at these issues from only one point of view. I decided to do an ethnographic study in a scientific setting, to see how biologists thought about some of these questions, she says. Also, I thought I should be including male reproductive processes as well. Fertilization research, she realized, would allow her to cover all the bases.  As she began her background studies, Martin was surprised to find that popular literature, textbooks, and even medical journals were crammed with descriptions of warrior sperm and damsel-in-distress eggs. Martin found that classic biology texts, for example, enthused about the human male’s amazing productivity--some 200 million sperm every hour--while practically complaining over the waste of the 2 million immature eggs present in the human female at birth, only some 400 of which the ovaries ever shed for possible fertilization, with the rest destined to degenerate over the woman’s lifetime. The real mystery, says Martin, is why the male’s vast production of sperm is not seen as wasteful.  Less mysterious, in Martin’s opinion, was the motivation for such biased language. Men link potency to strong sperm, she says. You’d like your sperm to be like you; no wonder everyone believed sperm were torpedoes. In all her searching, Martin came up with only a single depiction of less-than-mighty sperm: Woody Allen’s portrayal of a neurotic sperm nervous about his imminent ejaculation in the movie Everything You Always Wanted to Know About Sex But Were Afraid to Ask.  Woody Allen aside, the durability of the masterful-sperm imagery astonished Martin. It continued to dominate the contemporary technical and popular literature despite a growing body of evidence that the egg plays anything but a passive role. From the early 1970s on, studies of the sperm and eggs of many species have revealed that molecules released by the egg are critical to guiding and activating the sperm--that is, triggering the sperm to release proteins that help it adhere to the egg. In fact, the egg might just as well be called eager as passive. Among many species of lizards, insects, some crustaceans, and even turkeys, the egg doesn’t always wait for the sperm’s arrival. It can begin dividing without fertilization, and females can reproduce without sperm at all.  Yet none of this had made a dent in biologists’ language. When I asked them about it, they told me I had a point, says Martin. They claimed the imagery came up only when they needed to explain their research, and not in the lab. But I wanted to know what was really going on.  By 1986 Martin had begun hanging out with a team of researchers at Johns Hopkins who were observing sperm mobility in hopes of coming up with a strategy for a new contraceptive. They had started the year before with a simple experiment--measuring human sperm’s ability to escape and swim away from a tiny suction pipet placed against the side of the sperm cell’s head. To the team’s great surprise, the sperm turned out to be feeble swimmers; their heads thrashed from side to side ten times more vigorously than their bodies pushed forward. It makes sense, says Martin. The last thing you’d want a sperm to be is a highly effective burrower, because it would end up burrowing into the first obstacle it encountered. You want a sperm that’s good at getting away from things.  The team went on to determine that the sperm tries to pull its getaway act even on the egg itself, but is held down against its struggles by molecules on the surface of the egg that hook together with counterparts on the sperm’s surface, fastening the sperm until the egg can absorb it. Yet even after having revealed the sperm to be an escape artist and the egg to be a chemically active sperm catcher, even after discussing the egg’s role in tethering the sperm, the research team continued for another three years to describe the sperm’s role as actively penetrating the egg.  Meanwhile, Martin was keeping an eye on two other fertilization groups. They too seemed at times to disregard their own observations when writing about fertilization. Researchers at the University of Wisconsin, for example, described the way sea urchin sperm first make contact with an egg by quickly stringing together protein molecules into a filament that extends out until it reaches the egg. But instead of describing this as an innocuous process of assembly and attachment, the group wrote--in a pioneering paper that otherwise points out the egg’s ability to actively clasp and entwine--that the sperm’s filament shoots out and harpoons the egg. Likewise, when a researcher at the Roche Institute of Molecular Biology in Nutley, New Jersey, wrote in 1987 of his discovery that mouse eggs carry a molecular structure on their coating that fits inside a complementary structure on the sperm, helping bind the two together, he described the two structures, naturally enough, as a lock and key--but he called the egg’s protruding structure the lock and the sperm’s engulfing structure the key.  Martin doesn’t suggest that these researchers willfully distorted their imagery. In fact, she notes that one of the investigators at Johns Hopkins was her politically correct husband, Richard Cone. What’s more, Martin concedes that she herself was slow to recognize the disparity between the discoveries at Johns Hopkins and the way the findings were written up. It didn’t strike me for a few years, she says. But innocent or not, she adds, the cultural conditioning these biologists had absorbed early in their careers influenced more than their writing: it skewed their research. I believe, and my husband believes, and the lab believes, that they would have seen these results sooner if they hadn’t had these male- oriented images of sperm. In fact, biologists could have figured out a hundred years ago that sperm are weak forward-propulsion units, but it’s hard for men to accept the idea that sperm are best at escaping. The imagery you employ guides you to ask certain questions and to not ask certain others.  People preparing to dismiss Emily Martin as a humorless feminist have their work cut out for them. At once animated and easygoing in her cramped, cactus-strewn office, Martin chuckles as she goes through an inch- thick file of hapless-egg and macho-sperm imagery clipped from magazines. (In one Gary Larson cartoon, a housewife egg fends off a swarm of sperm trying to get past her by posing as phone repairmen, insurance salesmen, and UPS deliverymen.) I just think this stuff is a riot, she says. In fact, it’s the biologists who seem a little stuffy. Though she usually lectures to students, Martin recalls one lecture she gave to biologists at the Woods Hole Oceanographic Institution in 1990. It was one of the most painful experiences of my life, she says. I had gotten to the point where the audience is usually rolling in the aisles, and all I got was stony silence. I could see they were furious. On the other hand, I can understand their feelings; I get defensive when someone criticizes cultural anthropology.  One researcher who doesn’t bristle at Martin’s jabs is Scott Gilbert, a developmental biologist at Swarthmore College. Though he suggests Martin may go a little overboard in stressing the egg’s aggressiveness--for example, he prefers to think of the egg as engaging in a dialog with the sperm rather than gluing it down--he does believe her views are a vast improvement over the conventional explanations. Most studies clearly show that the sperm is attracted by the egg and activated by it, says Gilbert. But if you don’t have an interpretation of fertilization that allows you to look at the egg as active, you won’t look for the molecules that can prove it. You simply won’t find activities that you don’t visualize.  Now that the discrepancy between experiment and interpretation is being brought out into the open, the professional literature seems to be coming around--although a recent issue of the biology journal Cell Differentiation and Development placed on its cover a Prince Charming sperm delivering a wake-up kiss to a long-eyelashed Sleeping Beauty egg. As for the popular press, Gilbert and Martin cite the same recent example as particularly egregious: an article titled Sperm Wars that appeared as a cover story in a national science magazine whose name you’d recognize in a minute, which referred to the sperm cell as a formidable .00024-inch weapon, tipped with a chemical warhead (see DISCOVER, July 1991). On the other hand, Developmental Biology, the most popular college textbook in its subject area, takes great pains to point out the new, equal-opportunity view of fertilization. No wonder: Gilbert wrote it.  One reason the older interpretation is dying hard is that it tends to be self-reinforcing, not only in suggesting ready-made imagery that can skew observations but also in subtly determining who becomes a biologist in the first place. This business has stopped certain people from entering the field, says Gilbert. Why would a woman want to continue if people are telling her she’s passive?  Nevertheless, as Martin points out, a growing number of women are continuing in biology. But that won’t guarantee more evenhanded interpretations. Scientific training involves a rigorous socialization process that doesn’t allow for different perspectives, she says. It’s hard to say that women biologists are any less guilty of these things than men.  Even if biologists do move away from the passive-egg myth, other images are waiting in the wings. These days, says Martin, researchers seem ready to confer a spider woman aspect on the egg. Men have always turned to spider imagery when they are confronted with women who acquire power, she charges. Indeed, her file of magazine clippings contains several images in support of her claim. One striking example: the cartoonish silhouette employed as the emblem of the once-popular Charlie’s Angels television series, which depicts the three starring female characters, guns and all, unmistakably merged into the eight-limbed shape of a spider.  Though Martin is the first to insist that much of the fertilization imagery is good for a laugh, she doesn’t mean to let scientists dismiss it all as a big joke. People say, ‘Oh, what difference does it make?’ as if this stuff doesn’t affect anyone, she says. But our culture is affected by these powerful visual images. We all put so much faith in science, and so much of the negative load lands on women.  She notes, as another example, that it’s been known since the 1960s that women exposed to toxic chemicals bear children who run a higher risk of serious medical problems. Those findings reinforced the cultural notion that women should be sheltered, and some companies have rules to prevent women of reproductive age from working at jobs that might involve exposure to these chemicals. But only in the past few years have comparable studies shown that men exposed to high levels of lead, vinyl chloride, and about a dozen other chemicals also have children who are at higher risk. It’s the notion of invulnerable sperm, she claims, that made it take so long for scientists and the public to accept the male role in birth defects and infertility.  Martin has recently shifted her focus to metaphors used in other areas of medical research. For example, she says, when AIDS was seen as affecting only the ‘dregs’ of society, scientists described it as a monkey virus. Now that well-to-do white women are getting it, all of a sudden researchers are talking about AIDS being an autoimmune disease. There are, of course, other reasons that researchers’ language might change, including a growing knowledge of how the AIDS virus in fact wreaks havoc on the host’s immune system. Martin is still studying the literature and observing researchers in immunology labs. For now, she concedes, all you can do is raise a question. It’s often impossible to prove causality.  Although she is no longer studying fertilization imagery, Martin still lectures on the topic because, she contends, the work shows that science can have social effects. When we anthropomorphize the egg and sperm, when we turn them into a miniature bride and groom complete with personalities, what effect does this have on abortion legislation? These effects aren’t intended by scientists, but they happen. They blend moral and scientific issues together in a way that makes me want to stand up and say something.  There’s further irony in the traditional metaphors. The notion of fiercely battling, competitive sperm suggests that they’re battling each other in a race to the egg. In fact, says Cone, they have a hard time making their way through the mucus glop, and like a team of bicyclists they take turns up front parting strands of mucus. So in a sense sperm are cooperative. The egg, on the other hand, is the real competitive loner. Only one matures each month, and the one out in front suppresses the maturation of all the others. The macho image of sperm not only obscures this reality; it actually reverses what’s been observed.  Can biased metaphors be eliminated from science? Martin doesn’t think so. Even if they could be, she doesn’t think that antiseptically neutral language would be desirable. Metaphor is, after all, a powerful vehicle for creative thinking. The goal shouldn’t be to clean the imagery out, she says, but to be aware that it’s there. It also helps, she adds, to be able to take a joke. Humor takes away the sting, she says, along with the potential for inculcating harmful ideas.

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