I summed up, saying, “Harmful mutations could be the reason that most asexuals go extinct. At the moment, we can’t measure mutation rates directly, so we can’t yet settle the argument. If it turns out that mutation rates among asexuals are generally low, then mutations are not the reason after all. But if it turns out that mutation rates are generally quite high, then it follows that the improbable persistence of the bdelloid rotifers must be due to their having evolved some way to reduce the mutation rate that has eluded other asexuals. Perhaps—”
Suddenly, a mournful voice cut in, “Ah, but Miss Philodina, what about infectious diseases?” The screen on the wall had lit up again, and a face appeared. Grotesque, with huge scything mandibles, it looked like an escapee from one of my nightmares. The creature continued: “I am a nameless worker ant of the species Atta colombica. I hail from a thriving colony near the Panama Canal; we number more than two million. Long ago, long before humans were a twinkle in Mother Nature’s eye, my ancestors invented agriculture, and we have been proudly farming ever since. Although ants of other species farm livestock such as aphids, we farm fungus. Why? For the same reason humans farm wheat or rice. We farm it to eat it—and we cannot live without it. So we cut leaves and flowers from all sorts of different plants to make compost for the fungus to grow on; we manure the fungus with our excretions; we weed the garden where the fungus grows; we prune the fungus to make it more productive; and we try to protect the fungus from pests. We live in constant fear, however, of an event that would jeopardize the entire colony: an outbreak of Escovopsis.”
The ant shuddered down to the tips of her antennae. She continued: “Escovopsis is a virulent disease of the fungus, and if it breaks out, it will destroy the whole garden. This brings me to my question. Our fungus is also an ancient asexual. Not quite as ancient as you, Miss Philodina, but it is still thought to be a good twenty-three million years old. We propagate the fungus clonally, and when a new queen leaves her natal nest to start her own colony, she takes some cultivars of fungus with her, packed in special pockets in her throat. This means our fungus gardens are like modern human crops: they are monocultures, whole fields that are genetically identical. We think this is why they are particularly vulnerable to disease. We’ve heard that susceptibility to disease has a genetic component, so a disease that starts in a monoculture will, pardon the pun, have a field day, destroying everything. One reason sex may be an advantage is because the shuffling of genes gives an edge in the perennial battle against disease. So, Miss Philodina, how do you cope with this problem?”
Well, the ant had made an excellent point and brought us right to the third theory of why we need sex, the Red Queen.
As the ant said, susceptibility to infectious disease—or more generally, to parasites, whether viruses, bacteria, fungi, or other nasties—typically has a genetic component. Since asexuals keep the same genes (give or take a mutation or two) from one generation to the next, parasites can easily evolve to infiltrate their defenses, annihilating clones. In contrast, sex, by mixing up genes, prevents parasites from becoming too well adapted to their hosts. Sex is an advantage because it breaks up gene combinations: it creates the genetic version of a moving target. With each act of sex, the parasites have to start again from square one. The name of the theory, the Red Queen, comes from Through the Looking-Glass. Remember? The Red Queen says to Alice, “Now, here, you see, it takes all the running you can do, to keep in the same place.” In other words, you have to change to stay where you are.
Before Miss Philodina could marshal her arguments, the supercilious armadillo rose to his feet. The lights glinting off the back of his shiny carapace, he said: “If I might speak.” He waved a front leg dismissively. “I am a nine-banded armadillo, and I believe I am in an unusual position. Armadillos are rare, yes—I might even be so bold as to say unique—among mammals: we routinely engage in both sexual and asexual reproduction. When boy armadillo meets girl armadillo”—he sniggered—“I’ll spare you the details, but as I’m sure you know, armadillos are unusual in the length of their equipment. It has to be reinforced with special fibers, so you can just call me Mr. Big. Anyway, egg fuses with sperm, and that cell then splits and splits again to give four genetically identical embryos. Thus, I am genetically different from my parents, yes, but a clone of my brothers.
“But I digress. The real point of the Red Queen is this: sex is an advantage because it makes you rare. Monocultures are vulnerable to disease because all the individuals are the same clone. A field full of different clones would not be vulnerable, yes? The disease would not be able to sweep through and infect everybody.
“Ironically, successful clones are the cause of their own demise. As a clone increases in frequency, it becomes more vulnerable to disease, yes, for two reasons: first, a disease can spread easily between members of the same clone; and second, as it becomes more common, the disease has more chances to evolve to infiltrate the target.”
Everyone started whispering. The armadillo stamped his feet for attention. As the audience calmed down, he went on: “How do you avoid being common if you’re a clone? Easy. You go somewhere else. You see, when a clone arrives in a new area, yes, she will have all the benefits of being unique. Assuming she doesn’t carry her parasites with her and assuming the diseases she’s left behind are worse than the diseases in the new place, she should be able to go on without sex for as long as she can keep on the move.”
“Oh, of course! Our fungus travels!” said the ant.
“Yes, and in conditions that reduce the chances that Escovopsis goes with it,” said the armadillo. “I don’t know, but I’d guess that the cultivar of fungus the queen takes with her is chosen carefully, yes, and perhaps even disinfected.”
“Oh, Escovopsis never travels with the queen. We know that,” said the ant.
“So then the question to Miss Philodina is, do you travel? Is this how you outwit the Red Queen?” said the armadillo grandly.
I began to feel superfluous. But I guess this is a subject where everyone wants to put in their two cents. As for Miss Philodina, well, she looked livid. And she sounded it, too, replying snappishly, “The answer’s in my forthcoming book, The Seven Habits of Highly Successful Asexuals, which is, I’ll have you know, under embargo. But since you’ve as good as told the secret, I might as well spill the beans.
“I believe that travel is indeed the secret of our success. We bdelloids travel in both space and time. Of course, we can’t travel backward in time: nobody can do that. But we can go forward. We have a trick called anhydrobiosis. It’s a state of suspended animation. Essentially, we dry up and blow away.”
Someone in the audience sneered that the old crone was already dried up.
Miss Philodina pretended not to hear. “It’s risky. Anhydrobiosis is difficult,” she said. “Many bdelloids never recover. But if you do survive, you come back to life in a new place and time, healthier and happier than before.”
I made my last stab at taking back my show. Drying up and blowing away may not—by itself—be enough to make a successful career of asexuality, I pointed out. After all, other organisms have anhydrobiosis, and they are not ancient asexuals. I imagine, though, that this strange ability to travel in space and time is an important factor in the bdelloids’ success. Long-term success as an asexual is difficult—and almost certainly requires several quirks of fate.
By this point, I was exhausted. But the show had made a crucial point: although we don’t have a definitive answer, it looks like we need sex to stay healthy. Shuffling genes can help us evade parasites and reduces the impact of harmful mutations. In short, sex enables us to survive.
I concluded the show with a double warning: girls in most species would still be unwise to get rid of males altogether (this was greeted by boos from the radical feminists), and males—especially mammals—should avoid becoming complacent: “You male mammals may be busy congratulating yourselves. Of all the animals, mammals are the only ones where the asexual reproduc
tion of adults is unknown. Mammalian males have evolved to be indispensable—genetically at least. The cloning of adult mammals is not possible without heavy and, for the moment, unreliable technological hocus-pocus.
“So, men, you’re safe for now. But if you don’t want to be abolished, let me give you some advice. Asexuality is particularly attractive to girls in species where males are lazy and never give a hand with the child care. The benefits of asexuality are greatly reduced if males help out.”
Whew. I’d made it through without a riot’s breaking out or the plug’s being pulled. I thanked everyone for their questions and finished by calling for a big hand for Miss Philodina roseola: “Long live the bdelloid rotifers!” The audience burst into applause as I recited my tag line, “Predators, please remember that it is forbidden to eat guests as they leave. And all of you, join me again next week when we’ll put another deviant Under the Microscope!”
AGONY AND ECSTASY: A NOTE FROM DR. TATIANA
In my business I get asked a lot of questions. Many of them concern matters beyond the wildest human imaginings. But the most common question is mundane enough: Why did I become a sex expert? Quite simply, I decided to dedicate myself to sex when I realized that nothing in life is more important, more interesting—or more troublesome.
If not for sex, much of what is flamboyant and beautiful in nature would not exist. Plants would not bloom. Birds would not sing. Deer would not sprout antlers. Hearts would not beat so fast. But ask an assortment of creatures, what is sex? and they will give you different answers. Humans and many other species will say copulation. Frogs and most fish will say the squirting of eggs and sperm in joint shudders of spawning. Scorpions, millipedes, and salamanders will tell you that sex is packets of sperm deposited on the ground for the female to sit on so they’ll explode into her reproductive tract. A sea urchin will say sex is releasing eggs and sperm into the sea in the hope that they will, somehow, find each other in the waves. For flowering plants, sex is trusting the wind or an insect to carry pollen to a receptive female flower.
To succeed, each of these methods requires a suite of different features. A male flower who wishes to be a Lothario and have his pollen strewn to as many mates as possible must seduce not female flowers but bees. Other creatures must wear gaudy costumes, be they fancy feathers or frivolous fins; they must sing and dance for hours and hours; they must perform prodigious feats, building and rebuilding nests and bowers. In short, they must expend enormous energy shouting, “Choose me, choose me.” And all for—what?
In truth, these various practices are just the means to an end. The ultimate sex act—the act that all these antics have evolved to accomplish—is the mixing of genes, the creation of an individual with a new genetic makeup. To a miserable organism sitting alone in a singles bar, genetic mixing might not seem worth the bother. Yet it is fundamental to the grand scheme of things. To see why, let’s take a step back and think about how evolution works.
For most of us, caught up in the hurly-burly of our daily struggles, the purpose of life may seem elusive. But from an evolutionary point of view, the purposes of life are clear: survival and reproduction. If you fail at either, your genes go with you to the grave. If you succeed at both, you pass your genes on to your children. Inevitably—such is life—some organisms do better than others at surviving and reproducing. If everyone had identical genes, then differences in survival and reproduction would be due to luck, not genes. But usually individuals have different genes. And insofar as a particular gene confers an advantage in terms of survival or reproduction, that gene will spread.
This simple process, discovered by Charles Darwin and Alfred Russel Wallace in the nineteenth century, is the principal mechanism of evolution. It is known as natural selection. Sometimes the process is fast and easy to see. Suppose a poison—an antibiotic, say, or an insecticide—appears in the environment. And suppose that surviving the poison depends on having a particular gene. Those who do not have the gene will die, their genes “deselected” from the population. In the extreme case, no one has the resistance gene, everyone dies, and the population becomes extinct. More often than not, however, some individuals are fortunate and have a gene to resist the poison. Since these individuals are the only ones to survive and reproduce, the genetic makeup of the population will shift to one where everybody is resistant.
Thus, genetic variation is crucial: no genetic variation, no evolution. But where does genetic variation come from? There are two main sources: mutation—and sex. Mutation, or random changes to information contained in genes, is the more primitive of the two. Mutations arise from errors made by the cell’s genetic copying machinery. Since no scribe is perfect, some errors are inevitable—which is just as well. Whereas sex produces new combinations of genes that already exist, mutation creates altogether new genes—and thus generates the raw material of evolution. Without mutation, evolution would grind to a halt.
Yet mutation by itself is not enough. From time to time organisms evolve to give up sex, reproducing asexually instead. When this happens, any genetic differences between a parent and child are, by definition, due to mutation only. At first, asexual organisms often flourish. But their glory is fleeting. For reasons that remain mysterious, the loss of sex is almost always followed by swift extinction. Apparently, without sex you are doomed.
Which is not to say that sex makes life easy No matter how good your survival skills are—you can be the champion at evading predators, or have the best nose for finding food, or be immune to every disease—it will all be for naught if you cannot find, impress, and seduce a mate. Worse, success at seduction is often at odds with survival. If you’re a bird, flaunting an enormous tail may make you quite the cock among hens—but it may also make you lunch for a cat. Worse still, the competition for mates is often exceedingly stiff:
The upshot of all this is that the need to find and seduce a mate is among the most powerful forces in evolution. Perhaps nothing in life generates a more ecstatic diversity of tactics and stratagems, a more surprising array of forms and behaviors. In comparison, tricks to avoid predators seem predictable and limited. They typically include one or more of the following features: going about in groups, moving fast, blending in with your surroundings, looking scary, sporting a shell or sharp bits, or tasting revolting. But tricks to seduce a partner—ah, here the variety is endless. Which is why everyone asks so many questions.
And which is why I have dedicated my life to answering them. In the pages that follow, I have chosen samples of my correspondence over the years. I have deliberately selected questions that seem to me to address the concerns of all creatures, such as promiscuity, infidelity, and homosexuality. I have grouped questions on related topics into chapters, each of which has the briefest of introductions and concludes with a summary of my advice.
The chapters, in turn, fall into three related parts. In the first part, “Let Slip the Whores of War!” I reveal the reasons that males and females so often want different things from each other, and from life, and I explore some of the consequences. The second part, “The Evolution of Depravity,” discusses situations where the collision is at its most intense—sometimes generating horrific outcomes, including rape and cannibalism. This part finishes with a brief chapter on the rarest, most aberrant evolutionary phenomenon: monogamy.
The last section goes further still, to ask “Are Men Necessary?” Here, I consider various matters to do with the evolution of gender and of sex. In an attempt to find out why sex is so essential for long-term evolutionary success, the final chapter is a discussion with the only organism so far known to have succeeded in living for millions and millions of years without it.
What of my methods? To respond to my readers, I have sifted through the scientific literature, reading hundreds of books and papers; I have interviewed specialists on subjects from dwarf males to giant sperm. When the answer is not known to science, as often it is not, I have given my best guess based on the knowledge available and m
y understanding of natural selection. Sometimes, as a result of my research, I have come to conclusions that are different from the prevailing wisdom; thus, I hope that in a small way this book makes a contribution to ongoing debates. In that spirit of open scientific inquiry I have provided, at the end of the book, all my sources.
I have found from experience that most organisms prefer to be called by their common names rather than by their technical Latin names—after all, few humans talk of themselves as Homo sapiens—so I use Latin names only when necessary for clarity or when the organism I am discussing is too obscure (or too snobbish) to have a common name. In observance of scientific custom, I have given measurements in metric units. However, in those instances where I felt it would be helpful to my readers in North America, I have provided conversions. Finally, I would like to thank my correspondents for agreeing to let me make public problems of a most intimate nature. This book would not have been possible without them.
Praise for Dr. Tatiana’s Sex Advice to All Creation
“Witty, racy, informed, entertaining, and instructive … Judson is a gifted writer, and her book helps further understanding.”
—Science
“Judson’s witty, well-researched vignettes are a guilty pleasure, natural history that goes down as sweet as a trashy tell-all.”
—Outside magazine
“Captivating … An evolutionary biologist with interesting and amusing things to tell us.”
Dr. Tatiana's Sex Advice to All Creation Page 21