When I was a girl, I had a terror of cockroaches that bordered on pathological. This was a particularly inconvenient phobia for a person who lived in a proto-slummy apartment in the Bronx, where roaches had perfected the art of arrogant accomodation among humans who would as soon squash them as see them. My father would squash them with his bare hands. My mother would wield a paper towel or a shoe. My younger brother would stomp them out with whatever tool or appendage was closest to the oily cruds. Not I. No matter how many hundreds of roaches I saw, no matter how repeatedly I reminded myself that they lacked stinging or biting parts and really could not hurt me, I jumped and screeched every time one skittered into view. I could not be in a room with a visible roach and feel at peace, nor could I bear getting close enough to one to kill it. So if I opened a cupboard looking for a glass and instead found a roach, I'd go thirsty. Every evening, before venturing into the dark bathroom and switching on the light—an act that would be to roaches as reveille is to sleeping soldiers—I called my brother and begged him to minesweep the room ahead of time. Judging by the enthusiastic sound of slapping and hooting and stomping coming from within, my brother's task was substantial yet not unwelcome. "O.K," he'd say, emerging from the room and rubbing his hands together smartly, "I think I got them all."

To let you know how profound my terror was, I once woke up in the middle of the night and saw what I was sure was a big roach on the edge of my pillow, heading toward me. This was unheard of: as bustling as the roach population was, it had never bustled into bed with me. I yelped and leaped to my feet, but what was I going to do now? I couldn't very well wake my brother; my parents had little patience for my squeamishness; and above all, I could not kill the cockroach on my own.

I decided to cede my space to the enemy. I curled up at the foot of my bed, lying width-wise rather than lengthwise, knees to my chest, head flat on mattress. Uncomfortable and still scared, I nonetheless managed to fall back asleep. The next morning, I saw that the roach was nothing more than a piece of crayon, which had rolled back and forth on the pillow's indentation and so given me the midnight sense of something small, dark and alive.

I tell you all this now to let you know, in part, why I have named my book "The Beauty of the Beastly. I hated roaches then, and I still don't like sharing living quarters with them. But in this book, I give them their moment in the sun (whether the photophobic creatures appreciate it or not). I've learned details about cockroach biology that make me practically want to salute them. Their behavior, the variety of species in the family, the adaptations they have evolved to live with humans or, in most cases, without them—all are part of the great cockroach saga. It is the story of persistence, and resistance, of sensitivity and ceaseless change. Change is indeed the roach's trademark. In the essay called "There is Nothing Like a Roach," I mention the miraculous effectiveness of the pesticide Combat in keeping the urban roach population at bay. Combat still works better than an old-fashioned spritz from a can, but as of this writing, late 1994, the cockroaches in my Washington, D.C. apartment are starting to get the better of the little black disks. My kitchen is polka-dotted with two dozen Combat parlors, but still some roaches survive. Either the insects have at last evolved a mechanism for detoxifying the poison or—my belief—they have learned to avoid eating it in the first place. After all, I have known house mice clever enough to shun glue traps, leaping like Olympic hurdlers over a series of them in order to reach a bag of ramen noodles sitting on the other side. Clearly these mice had learned something by watching the fate of brethren who'd stepped on the traps. If mice can improve themselves through observation, rather than just mutation, why not roaches? And if that sort of elasticity, robustness and lust for life isn't beautiful, then not much good can be said for evolution, the mother of all invention, the one who stands by the side of the passing bio-marathon and cries, "Looking good! Keep it up! Stay alive! Stay alive."

The beauty of the natural world lies in the details, and most of those details are not the stuff of calendar art. I have made it a kind of hobby, almost a mission, to write about organisms that many people find repugnant: spiders, scorpions, parasites, worms, rattlesnakes, dung beetles, hyenas. I have done so both out of a perverse preference for subjects that other writers generally have ignored, and because I hope to inspire in readers an appreciation for diversity, for imagination, for the twisted, webbed, infinite possibility of the natural world. Every single story that nature tells is gorgeous. She is the original Shahrazade, always with one more surprise to shake down from her sleeve. Of course, I can record only a tiny fraction of those stories, but what I offer represents a larger plea, for all the stories that can be told, for the preservation of nature on her own terms, complete with the golums and creeps and ogres of the world, the roaches, the snakes, the bloodsuckers, the lowlifes and the brutes.

Beyond writing about the beauty of many stereotypical beasts, I also offer abundant evidence of the beastliness behind our conventional icons of beauty. Beloved dolphins can behave like sailors at Tailhook; orchids advertise faux merchandise; the legendary workers of the field—the birds, the bees, the beavers—in truth spend more time at leisure than the average European; and every creature cheats on its mate, or tries to. But even here, the less than exemplary behavior is beautiful in its subtlety. There is always more to be seen behind the first pass, behind the obvious traits that show up during early observations and that initially are used to pigeonhole a species or a social system or a gender. I love learning of new findings that overturn or at least complicate abiding verities, even when I may have written about those verities in the past. For example, I include in this book a story about female choice, a field of research that has exploded over the past decade or so. The idea here is that the female of many species is the choosy one when it comes to picking a mate, and that her pickiness serves a central role in the evolution of many of the more exaggerated properties observed in the male, like bright feathers or booming voices. That assumption is predicated on the comparatively high cost of reproduction to the female. She's the one who invests the most energy bearing and rearing young, so she is the one with the greatest incentive to select her mate carefully. The disparate cost of reproduction was thought to extend even down to the sex cells. A female's egg is big and filled with protein, fats, nutrients, molecular signals to start the embryo growing; a male's sperm is small and efficiently packaged, nothing more than a serving of genes wrapped in a slippery protein bullet. As the old scientific truism has it, eggs are expensive, sperm is cheap. Small wonder males so often seem willing to blow their pocket change at any opportunity.

Yet that simple split between the sexes turns out to be a bit too neat. Sperm is not so cheap after all; making it, in fact, substantially decreases the lifespan of experimental animals like flies and worms, and we can only wonder if it doesn't do the same to a few of our favorite higher organisms.

This recent insight by no means negates the importance of female choice to the evolution of male appearance and behavior. Females give a lot more of themselves to their young than eggs, after all. Mammalian mothers carry their babies around and offer up the breast; they have much incentive to be finicky about who fathers their children. Yet just knowing that sperm output exacts a substantial toll on its masculine maker puts the dynamics of sexual behavior in a new and more refined light. You see things you may have slighted before. You see the female make her choice, and then you see the male make his—embracing her as his newly beloved, or walking away, as though thinking to himself, this really isn't worth shaving a few minutes off my life.

In fact, if there is any lesson I have learned in my years of following science, it is that nothing is as it seems. Instead, things are as they seem plus the details you are just beginning to notice. New truths rarely overturn old ones; they simply add nuanced brushstrokes to the portrait. Dolphins may be mean-spirited at times, slashing at each other's flesh so brutally that they leave behind gouges, but they also engage in playful and tender behavior, jointly reaching decisions about when to travel, when to fish, when to rest. Hyenas sit at the top of the carnivore's pyramid, with all the ferocity that implies. Unlike lions, they consume every last body part of their prey—meat, fur, skull, bones. The moment two sibling hyenas emerge from the womb, they start mauling each other, usually to the death of one. Yet when a hyena is in a good mood—and if it knows and trusts you—it'll plop all 200 pounds of itself down on your lap like a pet and begged to be scratched behind the ears.

The sins of the anointed saints, the Jekylls beneath the hides—for these reasons I find it so much fun to think of the beasts I write about as protagonists, imperfect heroes all, playing out the drama of their circumstances and opportunities. And I anthropomorphize shamelessly. I assume that non-human species have personalities, intentions, emotions, awareness, even dreams and wishes. I do so for the sake of story-telling, and because the continuity of life on a genetic and morphological scale suggest a significant degree of fraternity among the creatures of the earth. Recently I saw an exhibit in a natural history museum displaying the skeletons of many different species: horses, alligators, monkeys, dogs, mice, birds, dolphins, humans. The exhibit made plain how often nature recycles her best inventions, how the limb bones articulate with the shoulders and hips in the same way whether the animal is a quadruped or biped, hoofer or flyer; how the ribs arc out from the spinal column in parallel parabolas; how the thigh is built of one thick bone, the calf of two slender bones; how we all have finger bones, even though the fingers may end up subsumed by flippers. We really are the same under the skin.

Seeing the similarity of skeletal engineering, I felt the usual mixture of contradictary emotions, of ego deflation and goofy communalism. Here I was, just another of nature's pre-fab animal kits, the standard-issue parts glued and stapled as though according to a numbered diagram, with scant innovation in arrangement beyond a slight widening of the pelvic bone.

At the same time, here I was, blessed with a design that had passed the test of a dozen geological epochs, evidence that life has really gotten the hang of it, of building a mobile body that is strong yet light, supple and enduring, a body that can spin, soar, leap, dig, climb, flee, swing—that can embody life. And I felt the beauty of how every beast, myself included, is born to move, to solve problems, to make the best of earth and gravity. And I thought that bodies built of such analogous components must surely house natures built of similar sensations and inclinations: fear, joy, curiousity, boredom, friendliness, antipathy.

This is not to say that all animals react the same to the same events (Obviously not. I may run away from roaches, but my cats will run fearlessly, even gleefully, toward them). But I take it for granted that other species are very much aware of themselves and their surroundings—that they have their particular version of consciousness. A spider consciousness. A cardinal grosbeak consciousness. This seems to me a mere act of courtesy, and also an admission of ignorance. We don't know what's in another creature's mind, so why assume it's a blank? Why assume the animal is a programmed robot, or a dumb brute, when to look at it, it seems to be acting with all the neurotic uncertainty you'd expect of any individual that's been thrown willy-nilly into the thick of life? Thus it was with real delight that I learned there is a vigorous debate among naturalists on the propriety of anthropomorphism (Chapter 27). The traditionalists insist it is sloppy science and that researchers should work tirelessly to keep their emotional objectivity, while the iconoclasts argue that you you can never understand another being unless you're willing to empathize with it. I come down roundly on the side of the anthropomorphists, although, not being a scientist and thus not required to back up my wooly notions with data, I'll go further than most, to the point where I'll anthropomorphize plants. We are learning too much about the complexities of plant defense and communication systems to dismiss the possibility that plants, too, have a grasp of themselves and their surroundings.

I also anthropomorphize molecules. Yes, proteins, nucleic acids, steroid hormones, they too are characters in little plays. They move, they spin, they embrace, they succeed or fail. I call the section about the molecular underpinnings of life "Dancing," because that's how I see in my mind what cannot be seen. But there are other ways of imagining the realms of the submicroscopic. Years ago I asked a protein crystallographer, who uses high-energy X-ray beams to map out the atomic structure of proteins, what proteins would look like if blown up to ordinary dimensions. He thought for a moment and then said, "Distorted nerf balls." "Fantastic!" I cried, and his image has stayed with me. The laborers of our body cells, the tens of thousands of proteins that perform core tasks regardless of whether we're aware or indifferent, are nothing more than colorful, squishable toys.

In delving into the science of molecular biology, I'll do anything to come up with spirited similes or metaphors. I do it for myself, to make the abstract concrete, and I do it in writing to keep the plot going. There's no denying that molecular science can be beastly in its difficulty, which is why people so often ignore it. But revolutions should not be ignored, and molecular biology is truly undergoing a revolution right now. As a science writer, I have sought to understand both the very large—the evolutionary processes that give us life as we see it today—and the very small, the micro-city that is the cell. Here is where science is making the most phenomenal progress, for the simple reason that progress is possible in molecular biology. The tools exist, and, unlike most evolutionary questions, the questions can be broken down into parts that can be analyzed in some meaningful, reproducible fashion. Scientists generally go after problems that can be solved, rather than any problem that strikes their fancy. So while we might wish that scientists were less reductionist, more holistic in their approach to understanding the nature of life, we must be sympathetic to what they are trying to do, which is to parse nature into knowabililty. Nothing lends itself to parsing more gracefully than the components of the cell.

In the section on molecular biology, beyond conveying specific stories about specific molecules, I try to give an impressionistic feel for what the issues are, the overarching concepts. With the Human Genome Project having been a public spectacle for some years now, DNA and genes have dominated both scientific and popular conceptions of how things work, how life comes to look as it does, why we think and feel and behave as we do. If only we could figure out the entire genetic code of a human being, the argument goes, we would have "it," the great it of selfhood, the recipe for a human being. We would have a chemical understanding of why one person retreats shyly from company while another cannot stand a moment alone; why one can play the violin so well while another has all the musicianship of a leaf blower; or why one person is gay, a second straight, a third a fetishizer of women's footwear. Alternatively, somebody will cry, "Don't forget the environment! Don't forget the nurture half of the nature-nurture equation." As though the proclamation of a dialectic gets us much further toward solving the enormous conundrum of how life assumes its form and patina. As though it means anything to say, 60 percent of intelligence is hereditary, 40 percent environmentally determined (or vice-versa; you choose the breakdown, for many numbers have been plugged into the two slots over the years). What, after all, counts as hereditary, and what environmental? People conventionally think of the term "environmental influences" as meaning the way your parents treat you as an infant, or the sorts of television shows you watch as an impressionable pre-schooler. But at this point, scientists consider the environment to encompass even things that happen to you before you're born, in the environment of your mother's uterus. Thus, if a pregnant woman is under enough stress that her hormonal balance changes, and if that change were demonstrated to have an impact on her baby, the effect would be called environmental. Similarly, should prenatal viral infection be shown to cause schizophrenia—a possibility now under investigation—that, too, would rank as an environmental, rather than an inherited, cause of the disease.

However, what if events in the womb end up influencing the fetal genes themselves? What if hormonal fluxes or some other chemical change in the uterus were to affect the expression of genes at crucial junctures of development, impelling some genes to turn on, others to turn off? Would the outcome of these alterations be considered the handiwork of the environment, or of genetics? We are entering a gray zone of biology here, where nature and nurture are so intermeshed that if you were to try decoupling them, you'd end up with nothing of any meaning. After all, development does not proceed in a void. The chemical sequences that we call genes, the strings of hundreds of A's, T's, G's and C's, cannot reach their potential and make us who we are without being within who we are; they find their purpose in a particular context, and, importantly, they are changed by that context. The double helix is a springy, ever-shifting molecule, the lava in the lamp. And as its form changes, so, too, may its function. A region of the helix doubles over, and a gene that once faced forward now tucks inward, where nothing can reach it to shake it awake. An errant hormone attaches itself to the genome like a piece of gum stuck to a movie seat, and that sequence is silenced for minutes, days, months. These are just a couple of examples of how the environment might have its say, and end up speaking in the language of genes.

I am interested in DNA as a being that moves in space and time, an organism in its own right. Therefore, most of the stories I tell of molecular biology are stories with a tactile, motile spin. I believe the importance of the structure of DNA has been grossly underestimated, and so I attempt in a small way to rectify that neglect. I write of DNA bending, the double helix as double pipecleaners, being folded and pleated and looped so that the genes arrayed along their span may be coaxed into speech; the histones, chunky Mickey Mouse-shaped protein groups that cling to the genetic material, condense it down to invisibility within the nucleus, and lord over all congress between the DNA and the rest of the cell; and the telomeres, redundant slats of genetic bases found at the tips of chromosomes that tell the cell how old it is, and how close it is to dying. These are features of the cell that are celebrated far less often than are the supposedly indomitable genes, yet they are among the elements that give sense and life to genes. They also serve as a bridge between the text of the speech as it is written in the nucleic acid subunits of the genes, and the sound, fury, busting-loose beauty of the body and brain as it is built. Where DNA exists in the round, that is where nature and nurture commingle.

Beyond describing specific characters—macroscopic or microscopic—I also explore themes that tie those characters together. In the section on adapting and elsewhere, I look at behaviors that humans and nonhumans alike often indulge in, but that in our current system of world marketeering earn scant attention and even less admiration: the fundamental need for play, for joy, for prolonged relaxation. I return repeatedly to stories of sexuality, of courtship rituals and mating strategies among a broad diversity of creatures. Part of my interest in animal sex is simple prurient curiosity: I like the details of how female meets male, how they circle one another warily, haughtily, venally, the style of their coming together, staying together, drifting apart. Sex stories are inherently interesting, and sometimes that's enough to justify the telling. Yet I often can't help but find a message in a given relationship, an insight into what is, and what could be—what the options are, the solutions to the abiding and imperious problem of perpetuity. An animal in its sexual prime is both universal life, behaving as life has from its inception, devoted above all to thrusting more life into the void of the future; and it is the particular, the individual lover, its heat making it new, immediate, its own hunger surely stronger than any hunger before it. A sexual animal is the inviolate individual, the most arrogant of creatures, believing itself for the moment one of the immortals; and the details of its story, of how male meets female, are everything, the only things. They are the creature rousing itself to its fullest potential, and they are the creature at its most complex, its most exposed, its most revealing. They are the animal crying, "Look at me! Watch me perform! I'm alive and I plan to stay alive by strutting my hour across the stage as it has never been strutted before. I am the most gorgeous, the most engaging, the most irresistible specimen you've ever seen. Look at me, I'm here!" So, o.k., I admit, I look.

Lest you think I'm a cheap voyeur, however, I include in the category of sexual behavior parental behavior as well. I believe that the two are strongly linked: how animals tend to their offspring is often a variation on the theme of their mating rituals, governed by similar hormones, as simple or as intricate as the affair that gave rise to the infants in the first place. This may, of course, be a reflection of my femaleness, for females in general cannot help but think of sex and motherhood as a package deal; and many of the evolutionary biologists who have argued that parental behavior should be considered a sexually selected trait, along with, say, the size of a male's plumage, have been women. Yet the truth is that most of the animals I've found interesting enough to write for reasons having nothing to do with their family life turn out to display noteworthy parental behavior. They offer up their bodies as breast equivalents, they eat feces just to get the nitrogen to protect their young, they strip apart rodents and turn them into predigested stew for the kiddies. Even some insects, alienist machines though they often appear to us, devote years to tending their young. Sometimes, the mating rituals that animals engage in hint at their capacity as caring parents, as, for example, when a courting male cichlid fish violently abuses a female to see if she'll fight back—and thus be a warrior when it comes to protecting her babies.

The theme of commonalities, of what we share with the other inhabitants of the planet, extends to our health and well-being. In the section on healing, I focus on medical and health issues, but from an evolutionary and cross-species perspective. As we descend into a state of national obesity, for example, we might benefit from considering how other mammals manage, metabolize and store their body fat. Why does fat fasten onto certain parts of the body so well and others hardly at all, and why is upper body fat so much more hazardous to our health than fat on the rump and thighs? Why does obesity make a person prone to heart disease and high blood pressure, while a woodchuck can become almost obscenely fat each fall without harming its arteries a single fat droplet? These are some of the piquant issues that arise when you take an evolutionary slant on a familiar topic, our fatness. The same can be said for menstruation. In Chapter XX, I present an revolutionary view of the purpose of periods that only an evolutionary biologist could have dreamed up.

One section, though, is devoted almost exclusively to human beings, that designated Creating. The creative impulse may not be confined to us—think of the bower-bird, or even the dung beetle and its flawless brood ball—but we have taken it far and away to the most extravagant heights; the n of possibility here approaches infinity. That idea struck me recently while thumbing through a magazine and coming across an advertisement—probably for a tourist agency pitching the wonders of Rome—that showed a few postage-sized details of paintings, by Raphael, Leonardo and Michelangelo. Small though they were, the pictures leaped off the page with their magnificence, leaped out of the magazine and its stubborn two-dimensional dailiness; they were not of the same stuff or species as the graphics or text that surrounded them. The same can be said for a line of Shakespeare, or Rilke, or Whitman; the roundness of the words, their intonation and texture, the swelling of one phrase, the stillness of the next, none of it sounds or tastes like ordinary language. With their genius, the artists strode far beyond humanness, or animalness, or beginnings, middles and ends—they disengaged themselves from the laws of nature or limits. And so I devote two chapters to the subject of art and genius, one exploring what science can reveal about the neurobiology of greatness, the other considering how the possession of a mortal body and its mortal ailments impinges on an artist's work. Not to limit the subject of creativity to the arts, I include stories about three exceptionally creative scientists, who not only are exploring the world as it is, but inventing it anew through the force of a synthesizing intelligence and imagination.

In the final section I return to a subject that knows no species boundaries, the cloak with room to cover us all—death. Here I take a molecular approach, an evolutionary approach and finally a personal approach to the topic. Emotionally, I hate and dread the thought of death; but intellectually, and from a biological point of view, it has a rightness to it, a force and simplicity. Life can be prolonged, but it can never be disengaged from death. Indeed, if you look at the genes that orchestrate the death of a cell—and cell death is the petit morte of which our grand bodily morte is made—they are the same genes that can be subtly altered into agents of immortality. But here's the catch: an immortal cell is a cancer cell. There is no escape, and if any beastliness has a sublime sort of beauty, it is the inviolate facelessness of death.

One last point. All the pieces that follow originally appeared in the New York Times, but they have been subtantially revised and personalized for this collection. That doesn't mean I've turned the book into stories about me—The Dung Beetle and I—or that I rely overmuch on personal pronouns, unless I'm there hands-on with the beast and want you to know exactly what it feels like to stare an angry three-foot rattlesnake in the eye while stroking its vibrating tail. Nor do I personally condone or believe in all the theories I present, a couple of them being, by the most generous description, highly speculative; but the ideas do reflect my sensibilities and ways of thinking about nature. If you only consider them long enough to snort in derision, at least I've kept you amused.