How Women Got Their Curves and Other Just-So Stories

Evolutionary Enigmas

David P Barash, Judith Eve Lipton

• Editorial: Columbia University Press
• Año: 2009
• ISBN:
  9780231518390
• Categoría: Sciences biologiques
• Categoría: Biologie

The authors of Gender Gap: The Biology of Male-Female Differences take readers on "a joyride of intellectual discovery... full of provocative ideas" (Pepper Schwartz, author of Prime ). So how did women get their curves? Why do they have breasts, while other mammals only develop breast tissue while lactating, and why do women menstruate, when virtually no other beings do so? What are the reasons for female orgasm? Why are human females kept in the dark about their own time of ovulation and maximum fertility, and why are they the only animals to experience menopause? David P. Barash and Judith Eve Lipton, coauthors of acclaimed books on human sexuality and gender, discuss the theories scientists have advanced to explain these evolutionary enigmas (sometimes called "Just-So stories" by their detractors) and present hypotheses of their own. Some scientific theories are based on legitimate empirical data, while others are pure speculation. Barash and Lipton distinguish between what is solid and what remains uncertain, skillfully incorporating their expert knowledge of biology, psychology, animal behavior, anthropology, and human sexuality into their entertaining critiques. Inviting readers to examine the evidence and draw their own conclusions, Barash and Lipton tell an evolutionary suspense story that captures the excitement and thrill of true scientific detection. "A delightful, thought-provoking volume on perennial questions about female biology... Along the way, they present a large amount of accessible information about biology, psychology, physiology and anatomy. Even more important, they demonstrate how scientists work to create and assess hypotheses while having a great deal of fun."— Publishers Weekly

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On Scientific
Mysteries
and
Just-So Stories

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“Ariddle wrapped in a mystery inside an enigma”—this is how Winston Churchill described Russia in 1939. The same can be said today of fully one-half the human race: women. Particularly enigmatic, it turns out, are their bodies.

And so please join us in exploring an array of unsolved evolutionary mysteries, such as: Why do women menstruate? Why do they have breasts when not lactating? Why do they conceal their ovulation, experience orgasm, undergo menopause? These detective stories aren’t “who-done-its” but rather “why-is-its,” and as it happens, most of them are sexual puzzles as well. Let’s be clear: these riddles and enigmas aren’t perplexing simply because they involve women, who—as everyone supposedly knows—are somehow mysterious, if only because they aren’t men. (“Why can’t a woman be more like a man?” wonders clueless Henry Higgins in My Fair Lady.) Rather, the traits in question are notable because they are typically found in women and only in women—that is, by and large they are biological novelties, not characteristic of other species. They are almost certainly fundamental to being human, stubborn stigmata of the unique evolutionary heritage of Homo sapiens, yet neither understood by scientists nor even acknowledged, for the most part, by the public as the puzzles that they are.

Moreover, most people are unaware that the traits in question are biological unknowns simply because nearly everyone takes the most intimate aspects of his or her life for granted, so deeply woven into our substantive human being that they are rarely identified as the perplexities they are. If you were to interview a hypothetical intelligent fish and inquire as to the nature of its environment, you would probably not hear “It is very wet down here.” The evolutionary enigmas of womankind are the ocean in which we swim—and by “we,” we do mean everyone, whether male or female.

To be sure, men aren’t altogether understood, either. Why, for example, do they develop facial hair (or, alternatively, why don’t women)? What is the evolutionary reason for male-pattern baldness? Or for that well-known reluctance to ask directions? Why are erections so predictably unpredictable: often appearing unbidden and unwanted among the young, then disappearing when wanted among the elderly? And does size matter? (If not, why does it seem to be such a big deal, at least psychologically, even if only to men themselves?) These “male mysteries” and many others will have to await another treatment and perhaps the identification of more questions worth asking as well as the unearthing of new leads worth pursuing.

For now, there is little doubt that certain characteristics of women pose enough unanswered biological questions to justify the asking. It is also clear that scientists have come up with enough evidence to reward the process and along the way to tickle the imagination.

Moreover, since each of the enigmas we are about to encounter has more than one possible explanation, but no single one is clearly correct, we’ll investigate many possible explanations in every case. Some of these explanations—or hypotheses, as scientists call them—may seem absurd.¹ Others are more reasonable. Some may even turn out to be true.

Most qualify as “Just-So Stories,” named after a delightful book of children’s tales by Rudyard Kipling, the famous winner of the 1907 Nobel Prize in Literature who was also a militarist, a supporter of British imperialism, and by most accounts a racist, although he did end his best-known poem with “You’re a better man than I am, Gungha Din!” The first of Kipling’s Just-So Stories, “How the Whale Got His Throat,” begins: “In the sea, once upon a time, O my Best Beloved, there was a Whale, and he ate fishes. He ate the starfish and the garfish, and the crab and the dab, and the plaice and the dace, and the skate and his mate, and the mackereel and the pickereel, and the really truly twirly-whirly eel. All the fishes he could find in all the sea he ate with his mouth—so!”² The book then proceeds to give fanciful accounts of “how the camel got his hump,” “how the rhinoceros got his skin,” “how the leopard got his spots,” and so forth. Testimony to Kipling’s effectiveness as a writer, a Just-So Story came to mean a delightful but empty fairy tale.

Ever since ethologists, geneticists, and ecologists joined together to create sociobiology, sometimes called “evolutionary psychology” when applied to human beings, they have had to contend with the accusation that their work consists of modern-day Just-So Stories, or imaginative accounts of how the biological world came to its current estate, how the various creatures are connected to one another, and—more controversially, at least for some—how the human species fits into this picture. Efforts to understand the intimate details of our own species have especially evoked the skeptical rejoinder “That’s merely a Just-So Story” when the hypothesized details are just that: conjectures lacking in supportive data and empirical validation. Among evolutionary biologists, this criticism can be scathing: to call something a Just-So Story is to dismiss it as unscientific poppycock.

We think it is time to stop running from Just-So Story as an epithet and to embrace its merits: not that science ends up being a Just-So Story, but that it generally begins as one, emerging from curiosity, questioning, and uncertainty. In the best cases, it then progresses to reasoned conjecture, to asking “What if?” and “Could it be?” and then, if the imagined story seems worth pursuing and is in fact pursuable, to validation—or, as philosopher Karl Popper and his devotees would have it, to in validation if not true—and, if productive, to further refinement.³ The enterprise is steeped in wonder—a description that includes, not coincidentally, both meanings of this term: an experience of amazement and appreciation (“the wonder of it all”) as well as the act of imaginative inquiry (“I wonder if the continents moved” or “I wonder if matter is actually composed of tiny, irreducible particles”). Between wonder (in either sense) and scientific “fact,” there are Just-So Stories.

For some, a Just-So Story is an unverifiable and unfalsifiable narrative. As such, it may be great fun, but it is also inherently unscientific. For others—including ourselves—a Just-So Story is simply a story: a tentative, proposed, speculative answer to a question and therefore a clarification of one’s thinking, ideally a goad to further thought and, not incidentally, a necessary preliminary to obtaining the kind of additional information that helps answer such questions (in the best cases, leading to yet more questions). When this happens—when the narrative is testable and leads to fact-based research—then, in a sense, it is no longer a Just-So Story, but science, pure but rarely simple and more often complicated.

Explanations labeled Just-So Stories are sometimes in fact legitimate empirical questions, which is to say they are falsifiable—if not based on currently available information, then at least potentially so in the future. It bears emphasizing that not all explanations are equally valid and that science arrives at conclusions based on evidence, as opposed to a postmodernist approach in which every “reality” is imagined to be equally valid. However, it sometimes takes a while to determine whether pure speculation, as seductive and appealing as it may be, actually connects to reality. String theory in physics, for example, does not currently have empirical support, and thus, strictly speaking, it may or may not be scientifically valid. But string theory has been immensely productive of additional research even if, according to some of its critics, it may have a downside as well. Such downsides, if and when they occur, are likely associated with “stories” that are scientific dead ends. Phlogiston was just such a dead end, as was “caloric,” “ether,” and the pre-Copernican, geocentric universe. But the only way to know for certain that a particular path is a dead end is to walk down it a bit and see what happens.

What is the alternative to proposing a Just-So Story, a speculation as to how things came to be the way they are? One possibility, of course, is to say that God did it. Another is to say, like Topsy, that the wings of birds and the echo-location of bats and the eyesight of eagles and the breasts of women “just growed” for no particular reason at all.⁴ In this case, we would be stuck with supposed “explanations” that didn’t explain anything; perhaps, therefore, we should talk about “Just-Growed” Stories.⁵ We prefer the Just-So variety, especially when strongly tinged with a whiff of adaptive significance—that is, when the speculation is based on a plausible relationship between the trait in question and how its possessors might have been “positively selected,” or how they are likely to have evolved because they enjoyed somewhat more success in projecting their genes into the future. If the speculation is testable, then so much the better: Just-So becomes Just-Right.

Hypotheses based on evolution include predictions about the trait in question: when it is likely to occur, to what degree, the kind of individuals likely to manifest it, and so on. Accordingly, purists (many of them defenders of exactly this approach) may argue that most of the hypotheses considered in the pages ahead aren’t really Just-So Stories at all, but rather science. We think they “doth protest too much,” that the boundary between Just-So Stories in the Kiplingesque sense and the positing of testable hypotheses in the scientific sense is often indistinct and that Just-So Stories not only often lead to reputable science, but are typically a prerequisite for it.

In this book, we hope to rescue the baby—the thoughtful, imaginative search for explanations—from being seen as contaminated by the supposedly dirty bath water of “unscientific” yarn spinning. We prefer science to “mere guessing,” but we’ll take the latter any time over the more rigid alternative: keeping silent unless and until the guesses or stories or hypotheses can be fully evaluated and subjected to rigorous statistical testing. Just So you know.

The stories we tell here involve mostly women. Of course, there is nothing new in wondering about them. It has long been claimed that women are mysterious. Freud’s description of female psychology as a “dark continent” appears today not only quaint, but patriarchal and patronizing, even though strictly speaking he was correct: women are indeed puzzling when it comes to the workings of their minds. But so are men. At the same time, most people have no idea how many secrets are hidden within women, all of whom pose biological conundrums that are genuinely unique to them not only as individuals, but also as women.

In 1999, science journalist Natalie Angier wrote Woman: An Intimate Geography.⁶ Her excellent book surveys the female body, with different chapters devoted to various anatomic “continents,” such as the ovaries, uterus, clitoris, and so forth. Instead of focusing, as Angier does, on what is known about the anatomy of women, we look at what is not known, all the while suggesting possible answers. If Angier’s Woman is a “geography,” examining the corporeal female map, our book explores those regions that are currently off the charts. Referring to such places, ancient cartographers used to write, Hic Sunt Dracones (Here There Be Dragons). We say: “Here there be mysteries … and here are some possible explanations for them.” We thus offer a different kind of map, created by biologists and focused not on female body parts (with one exception), but on dynamic traits such as concealed ovulation, orgasm, menopause, and so on, all united in the personal trajectory of every woman. Our explanations are intended for anyone—male or female—interested in navigating the complexities of human life. We describe the female body as the biological enigma that it is, pointing out the unknown terrain, suggesting where other explorers have gone astray, and proposing new directions.

It has become fashionable—at least in some quarters—to speak of “the death of science,” that we have already finished with the big stuff, so all we have left to do is just some “mopping up.” We proclaim the opposite: science isn’t dead. It isn’t even sick, and its mission assuredly is not accomplished. There is a huge amount that we do not know; to a significant extent, in fact, we don’t even know what we don’t know!

Science courses and even science writing for the lay person often regrettably give the opposite impression because they nearly always present what is known. This approach seems logical, if only because nature does not give up its secrets readily, and scientists are understandably proud of what has been discovered; like our colleagues, we are eager to share the bounty. And yet this approach—so widely expected and dutifully followed—is also misleading because in fact there is much more that we don’t know. In a perhaps overused simile, science is like a flashlight or a lantern that ideally helps searchers to find their way. But even though the light of current scientific research may be bright, it thus far illuminates only a tiny proportion of the total. We are still largely in the dark.

We mean this neither as a reverential, philosophic statement of epistemic mystery, reflecting the impossibility that science will ever come to grips with the ineffable, nor as a genuflection toward fashionable postmodernist puffery according to which the natural world can be grasped only as a narrow, culture-bound “narrative” because everything—even the basic principles and empirical findings of physics, chemistry, and biology—is “socially constructed.” We believe in science and in its capacity to provide yet more illumination—and so do you, if you fly in airplanes, use a computer, or take antibiotics when prescribed. But we also believe that science is most exciting as a process rather than as a recitation of what has already been discovered.

We also believe that it is possible—indeed, essential—for science to operate from a stance of maximum possible objectivity. To understand quanta, molecules, genomes, ecosystems, or galaxies, it is necessary to step outside (metaphorically at least) and treat these subjects as objects. Ditto for the human kidney, brain, and immune system, as well as for the topics to be covered in this book: menstruation, concealed ovulation, breasts, orgasm, and menopause. Accordingly, we wish to plead guilty, right at the start, of objectifying women—or, rather, of objectifying those aspects of women that we are hoping to illuminate and understand—in order to give them and their mysteries the objective, scientific attention they deserve but have only rarely received.

This book is also unusual in that we try to stand in the light while gesturing toward the surrounding dark, making guesses, spinning yarns, telling stories of varying degrees of likely validity. We take this approach not because we think it will always remain dark or because we favor a hushed acceptance or even an embrace of science’s limitations. Quite the opposite: we hope to inspire our readers to think about what might be out there just beyond the present circle of science’s bright light, possibly even to explore some of the shadows, and (not least) to get some intellectual exercise and have fun in the process.

In our case, that process is biology—evolutionary biology, in particular. Here, too, the nonspecialist reader will encounter something a bit out of the ordinary. Not only will we be examining things that evolutionary science does not know, but we’ll be concerned largely with a kind of knowing that may itself be unfamiliar. Thus, when biologists traditionally inquire into the causes of something, they generally mean, “What makes it happen?” For example, many North American birds migrate twice each year: south in winter and north in summer. Trying to understand what makes birds migrate, biologists might investigate changes in food availability, in temperature, and in day length (which, incidentally, is key for most species). Or they might study how the relevant environmental cue influences a bird’s behavior: Which senses are involved, which brain regions, which hormones? All these approaches are perfectly reasonable, important, and worthwhile.

But they are also somewhat limited. In particular, they share a focus on immediate causation, involving proximate mechanisms—so named because they all deal with nearby, directly causative factors. They tend to neglect another realm of causation, a somewhat more distant but no less valid approach, involving distal or ultimate mechanisms. Thus, whatever environmental cue hastens bird migration and whatever its hormonal or neural activation pattern, migration would not take place unless there were some underlying advantage—in other words, some evolutionary reason—for doing it. Red-winged blackbirds migrate, black-capped chickadees don’t. Yet for both species the days shorten and then lengthen identically; both species have eyes to perceive changes in daily illumination; both have brain regions that can respond to them; both have the same available palette of hormones. The proximate mechanisms that eventuate in migration by red-winged blackbirds clearly do not operate in black-capped chickadees. Why not? What makes it happen in one case and not in another?

Those seeking to answer these questions find themselves in the realm of distal or ultimate mechanisms. In this case, why has evolution equipped red-winged blackbirds with proximate mechanisms that produce migration, but not black-capped chickadees? The difference presumably has something to do with migration being adaptive for the former, but not for the latter. In other words, the trait in question—in our example, migration—somehow helps blackbird genes get themselves projected into the future, but would have a very different effect on chickadee genes. Understanding that adaptive “something” is evolutionary biologists’ goal, in pursuit of which they would likely study the costs and benefits of migration for the two species. What are the pros and cons of migrating or of staying put if you are a blackbird or a chickadee?

In the pages to come, we are especially concerned with distal or ultimate mechanisms, with what evolutionary...