Stunkard was only a little coy about how this rule of parasites could apply to humans. “It may be applied to any group of organisms, and is not intended to refer merely to political entities, although certain implications may be in order.” With its complete surrender of its liberty, the parasite had entered the “welfare state,” as Stunkard put it—with hardly a tissue of metaphor dividing the tapeworm and the New Deal. Once parasites gave up their freedom, they rarely managed to regain it; instead, they channeled their energies into making new generations of parasites. Their only innovations were weird kinds of reproduction. Flukes alternated their forms between generations, reproducing sexually in humans and asexually in snails. Tapeworms could produced a million eggs a day. How could Stunkard have had anything but fast-breeding welfare families in mind? “Such a welfare state exists only for those lucky individuals, the favored few, who are able to cajole or compel others to provide the welfare,” he wrote. “The well-worn attempt to obtain comfort without effort, to get something for nothing, persists as one of the illusions that in all ages has intrigued and misled the unwary.”
Writing in 1955, Stunkard represented a dying gasp of the old take on evolution. As he was attacking food-stamp parasites, his fellow biologists were unceremoniously dumping the whole foundation of his scientific view. They discovered that every living thing on Earth carries genetic information in its cells in the form of DNA, a molecule in the shape of a double helix. Genes (particular stretches of DNA) carried the instructions for making proteins, and these proteins could build eyes, digest food, regulate the creation of other proteins, and do thousands of other things. Each generation passed its DNA to the next, and along the way the genes got shuffled into new combinations. Sometimes mutations to the genes turned up, creating new codes altogether. Evolution, these biologists realized, was built on these genes and the way they rose and fell as time passed—not on some mysterious inner force. The genes offered up rich variety, and natural selection preserved certain kinds. From these genetic ebbs and flows new species could be created, new body plans. And since evolution was grounded on the short-term effects of natural selection, biologists no longer had any need for an inner drive for evolution, no longer saw life as a plastic Christmas tree.
Parasites should have benefited from this change of scientific heart. They were no longer the backward pariahs of biology. Yet, well into the twentieth century, parasites still couldn’t escape Lankester’s stigma. The contempt survived both in science and beyond it. Hitler’s racial myths have collapsed, and the only people who still believe in eradicating social parasites are at the fringes, among the Aryan skinheads and the minor dictators. Yet, the word parasite still carries the same insulting charge. Likewise, for much of the twentieth century, biologists thought of parasites as minor degenerates, mildly amusing but insignificant to the pageant of life. When ecologists looked at how the sun’s energy streamed through plants and into animals, parasites were nothing more than grotesque footnotes. What little evolution parasites experienced was the result of being dragged along by their hosts.
Even in 1989, Konrad Lorenz, the great pioneer in animal behavior, was writing about the “retrograde evolution” of parasites. He didn’t want to call it degeneration—that word was perhaps too loaded by Nazi rhetoric—and so he replaced it with “sacculinasation,” after Sacculina, Lankester’s backsliding barnacle. “When we use the terms ‘higher and lower’ in reference to living creatures and to cultures alike,” he wrote, “our evaluation refers directly to the amount of information, of knowledge, conscious or unconscious, inherent in these living systems.” And according to this scale, Lorenz despised parasites: “If one judges the adapted forms of the parasites according to the amounts of retrogressed information, one finds a loss of information that coincides with and completely confirms the low estimation we have of them and how we feel about them. The mature Sacculina carcini has no information about any of the particularities and singularities of its habitat; the only thing it knows anything about is its host.” Much like Lankester 110 years earlier, Lorenz saw the only virtue of parasites as a warning to humans. “A retrogression of specific human characteristics and capacities conjures up the terrifying specter of the less than human, even of the inhuman.”
From Lankester to Lorenz, scientists have gotten it wrong. Parasites are complex, highly adapted creatures that are at the heart of the story of life. If there hadn’t been such high walls dividing scientists who study life—the zoologists, the immunologists, the mathematical biologists, the ecologists—parasites might have been recognized sooner as not disgusting, or at least not merely disgusting. If parasites were so feeble, so lazy, how was it that they could manage to live inside every free-living species and infect billions of people? How could they change with time so that medicines that could once treat them became useless? How could parasites defy vaccines, which could corral brutal killers like smallpox and polio?
The problem comes down to the fact that scientists at the beginning of this century thought they had everything figured out. They knew how diseases were caused and how to treat some of them; they knew how life evolved. They didn’t respect the depth of their ignorance. They should have borne in mind the words of Steenstrup, the biologist who had first shown that parasites were unlike anything else on Earth. Steenstrup had it right in 1845 when he wrote, “I believe that I have given only the first rough outlines of a province of a great terra incognita which lies unexplored before us and the exploration of which promises a return such as we can at present scarcely appreciate.”
2
Terra Incognita
May I never lose you, oh, my generous host, oh, my universe. Just as the air you breathe, and the light you enjoy are for you, so you are for me.
Raquel Welch would have fared pretty poorly without her submarine. Suppose she had been shrunk down to the size of a pinhead and then had to get into the bloodstream of the dying diplomat on her own. Even if she could have clawed her way through the tough layers of skin and wiggled into a blood vessel, she would then have been sent flailing through his circulatory system by the pulsing push of his heart. Let’s say, for the sake of argument, that she could wear a scuba-like mask that could pull the oxygen out of the blood so she could breathe. She’d still suffocate if she ended up in some part of the body where there’s hardly any oxygen at all, like the liver. And as she tumbled through the darkness she’d be utterly lost, with no idea whether she was in the vena cava or the carotid artery.
The inside of a body is a tough place to survive. With our air-breathing lungs, our ears finely tuned to the vibrations of the air, we are adapted to life on land. A shark is made for the sea, ramming water through its gills and smelling for prey miles away. Parasites live in a different habitat altogether, one for which they are precisely adapted in ways that scientists only barely understand. Parasites can navigate through their murky labyrinth; they can glide through skin and gristle; they can pass unscathed through the cauldron of the stomach. They can turn just about every organ in the body—the eustachian tube, the gill, the brain, the bladder, the Achilles tendon—into their home. They can rebuild parts of the host’s body to suit their own comfort. They can feed on almost anything: blood, gut lining, liver, snot. They can make their host’s body bring them food.