To Lankester, Darwin’s theory had brought a unity to biology as impressive as that in any other science. He had no patience for doddering dons who looked at his science as a quaint hobby. “We are no longer content to see biology scoffed at as inexact or gently dropped as natural history or praised for her relation to medicine. On the contrary, biology is the science whose development belongs to the day,” he declared. And its understanding would help free future generations from stupid orthodoxies of all sorts: “the jack-in-office, the pompous official, the petulant commander, the ignorant pedagogue.” It would help carry human civilization upward, as life itself had been striving for millions of years. He laid out this view of the biological and political order of things in an essay he wrote in 1879, titled “Degeneration: A Chapter in Darwinism.”
The tree of life you find described in that essay isn’t the wild bush of Darwin. It’s shaped like a plastic Christmas tree, with branches sticking out to the side from a main shaft, which rises to higher and higher glories until it reaches humans at the top. At each stage in the rise of life, some species abandoned the struggle, comfortable with the level of complexity they had achieved—a mere amoeba, sponge, or worm—while others kept striving upward.
But there were some drooping branches on Lankester’s tree. Some species not only stopped rising but actually surrendered some of their accomplishments. They degenerated, their bodies simplifying as they accommodated themselves to an easier life. For biologists of Lankester’s day, parasites were the sine qua non of degenerates, whether they were animals or single-celled protozoa that had given up a free life. To Lankester, the quintessential parasite was a miserable barnacle named Sacculina carcini. When it first hatched from its egg, it had a head, a mouth, a tail, a body divided into segments, and legs, which is exactly what you’d expect from a barnacle or any other crustacean. But rather than growing into an animal that searched and struggled for its own food, Sacculina instead found itself a crab and wiggled into its shell. Once inside, Sacculina quickly degenerated, losing its segments, its legs, its tail, even its mouth. Instead, it grew a set of rootlike tendrils, which spread throughout the crab’s body. It then used these roots to absorb food from the crab’s body, having degenerated to the state of a mere plant. “Let the parasitic life once be secured,” Lankester warned, “and away go legs, jaws, eyes, and ears; the active, highly gifted crab may become a mere sac, absorbing nourishment and laying eggs.”
Since there was no divide between the ascent of life and the history of civilization, Lankester saw in parasites a grave warning for humans. Parasites degenerated “just as an active healthy man sometimes degenerates when he becomes suddenly possessed of a fortune; or as Rome degenerated when possessed of the riches of the ancient world. The habit of parasitism clearly acts upon animal organization in this way.” To Lankester, the Maya, living in the shadows of the abandoned temples of their ancestors, were degenerates, just as Victorian Europeans were pale imitations of the glorious ancient Greeks. “Possibly we are all drifting,” he fretted, “tending to the condition of intellectual Barnacles.”
An uninterrupted flow from nature to civilization meant that biology and morality were interchangeable. People of Lankester’s day took to condemning nature and then using nature in turn as an authority to condemn other people. His essay inspired a writer named Henry Drummond to publish a best-selling screed, Natural Law in the Spiritual World, in 1883. Drummond declared that parasitism “is one of the gravest crimes in nature. It is a breach of the law of Evolution. Thou shalt evolve, thou shalt develop all thy faculties to the full, thou shalt attain to the highest conceivable perfection of thy race—and so perfect thy race—this is the first and greatest commandment of Nature. But the parasite has no thought for its race, or for its perfection in any shape or form. It wants two things—food and shelter. How it gets them is of no moment. Each member lives exclusively on its own account, an isolated, indolent, selfish, and backsliding life.” People were no different: “All those individuals who have secured a hasty wealth by the chances of speculation; all children of fortune; all victims of inheritance; all social sponges; all satellites of the court; all beggards of the market-place—all these are living and unlying witness to the unalterable retributions of the law of parasitism.”
People had been referred to as parasites before the late 1800s, but Lankester and other scientists gave the metaphor a precision, a transparency, that it never had before. And it’s a short walk from Drummond’s rhetoric to genocide. Listen to how closely his line about the highest conceivable perfection of a race meshes with these words: “In the struggle for daily bread all those who are weak and sickly or less determined succumb, while the struggle of the males for the females grants the right or opportunity to propagate only to the healthiest. And struggle is always a means for improving a species’ health and power of resistance and therefore, a cause of its higher development.” The author of these words wasn’t an evolutionary biologist but a petty Austrian politician who would go on to exterminate six million Jews.
Adolf Hitler relied on a confused, third-rate version of evolution. He imagined that Jews and other “degenerate” races were parasites, and he took the metaphor even further, seeing them as a threat to the health of their host, the Aryan race. It was the function of a nation to preserve the evolutionary health of its race, and so it had to rid the parasite from its host. Hitler probed every hidden turn of the parasite metaphor. He charted the course of the Jewish “infestation,” as it spread to labor unions, the stock exchange, the economy, and cultural life. The Jew, he claimed, was “only and always a parasite in the body of other peoples. That he sometimes left his previous living space has nothing to do with his own purpose, but results from the fact that from time to time he was thrown out by the host nations he had misused. His spreading is a typical phenomenon for all parasites; he always seeks a new feeding ground for his race.”
Nazis weren’t the only ones to burn the brand of parasite on their enemies. To Marx and Lenin, the bourgeoisie and the bureaucrats were parasites that society had to get rid of. An exquisitely biological take on socialism appeared in 1898, when a pamphleteer named John Brown wrote a book called Parasitic Wealth or Money Reform: A Manifesto to the People of the United States and to the Workers of the World. He complained of how three-quarters of the country’s money was concentrated in the hands of 3 percent of the population, that the rich sucked the wealth of the nation away, that their protected industries flourished at the people’s expense. And, like Drummond or Hitler, he saw his enemies precisely reflected in nature, in the way parasitic wasps live in caterpillars. “With the refinement of innate cruelty,” he wrote, “these parasites eat their way into the living substance of their unwilling but helpless host, avoiding all the vital parts to prolong the agony of a lingering death.”
Parasitologists themselves sometimes helped consecrate the human parasite. As late as 1955, a leading American parasitologist, Horace Stunkard, was carrying on Lankester’s conceit in an essay published in the journal Science, titled “Freedom, bondage, and the welfare state.” “Since zoology is concerned with the facts and principles of animal life, information obtained from the study of other animals is applicable to the human species,” he wrote. All animals were driven by the need for food, shelter, and the chance to reproduce. In many cases, fear drove them to give up their freedom for some measure of security, only to be trapped in permanent dependency. Conspicuous among security-seeking animals were creatures such as clams, corals, and sea squirts, which anchored themselves to the ocean floor in order to filter the passing sea water for food. But none could compare with the parasites. Time after time in the history of life, free-living organisms had surrendered their liberty to become parasites in exchange for an escape from the dangers of life. Evolution then took them down a degenerate path. “When other food sources were insufficient, what would be easier than to feed upon the tissues of the host? The dependent animal is proverbially looking for the easy way.”