Expert Cites Germs, Not Genes, in Disease
AMHERST, Mass. — Paul W. Ewald’s best thinking started with an attack of diarrhea on a field trip to Kansas.
A zoologist, he was studying the social habits of sparrows. But during that ordeal 24 years ago, he had time to ponder other things: Was his personal predicament simply the havoc of a germ bent on spreading itself around? Or was his body trying to flush away the germ? Was this the evolutionary adaptation of an invader or the evolved human defense against it?
Healthy again, he checked the medical literature. “I realized that virtually all considerations of evolutionary processes in the medical literature were incorrect,” he says.
So he set out to fix that. Although not a physician, Ewald has applied the insights of 19th century evolutionary thinker Charles Darwin to help pioneer a perspective on disease now known as Darwinian, or evolutionary, medicine. Ewald has concluded that mainstream medicine, fixated on genes and lifestyle, is overlooking the chief cause of the most enduring, widespread and harmful illnesses of humankind.
Heart disease? He suspects germs. Cancer? Probably infection by germs. Mental illness? Also germs.
With a few colleagues, he has promoted a modest research renaissance in the germ theory of disease, which has been largely overshadowed by other ideas since polio, smallpox, tuberculosis and other perennial scourges were unmasked as infectious many decades ago. The scientific proof is mounting that Ewald could be right--at least in saying that germs have been underestimated--about a second wave of diseases.
For example, peptic ulcers, long tied to stress and overachieving personalities, are now widely blamed on the Helicobacter pylori bacterium and often treated with antibiotics. Cervical cancer has been traced to the human papilloma virus, which also causes genital warts.
Ewald didn’t make these discoveries, but he has pounced on them as evidence that genetics and environment have been overstated as contributors to disease and that the best germ research lies ahead.
“Infectious medicine has always been underestimated,” says Ewald. “The problem is that infectious diseases are extremely diverse.”
Confronting such a vast array, his thinking has transcended the boundaries of his formal training and specialized confines of most scientific thought. His latest book, “Plague Time: How Stealth Infections Cause Cancers, Heart Disease, and Other Deadly Ailments,” published in October, spans the history of medicine from the bubonic plague to the Human Genome Project. Ewald, a 47-year-old Amherst College biology professor, wrote the book for the lay public with plain language and a flair for storytelling rare in science.
Many scientists, including some evolutionary medicine advocates, wonder if Ewald goes too far in the sweep of his germ theory. “I’m made uncomfortable by global generalizations,” says University of Michigan psychiatrist Randolph Nesse. “They make some scientists think that Darwinian medicine is something different from regular medicine in terms of its standards.”
But Ewald says his ideas are “supposed to jar people out of the complacency they feel about modern medicine.”
Ewald portrays disease as primitive warfare. Viruses, bacteria and other microscopic creatures penetrate the body’s defenses. Once inside, they feast on humans, multiply and then go looking for new bodies to overrun.
Over time, humans evolve new defenses or invent protections like antibiotics and vaccines. However, germs, which can breed new generations every half hour or less, evolve rapidly to defeat the latest defenses. Ewald argues that new antibiotics are bound to lose ground to fast-evolving germs.
However, he says humans can favor benign germs by making life tougher on harmful forms. Better sanitation blockades the worst strains of cholera, which ride the water supply to find new human hosts. When there’s no easy route, evolution gives the advantage to more friendly cholera germs--those that survive longer inside a human without being lethal. Ewald says vaccines should be designed to disarm only the harmful parts of germs, encouraging the evolution of gentler forms.
In one of his central insights, he says genetic diseases cannot evolve and wage battle like germs, because human genetic mutations are too rare. If a genetic disease is both harmful and common, it should kill off the humans who carry it and fail to replenish itself quickly enough through mutations to persist over many successive human generations. Therefore, Ewald reasons, widespread ailments like heart disease, cancer and many mental illnesses should stem mainly from evolving germs, not bad genes.
He also thinks the role of chemical pollutants in causing sickness is overstated. The human body, he says, is adapted to handle low levels of chemicals, and few are pervasive enough in high enough amounts to explain many major illnesses outright.
Mainstream researchers view many diseases as a delicate interplay of all these factors: genes, environmental agents such as cigarette smoke or asbestos, and--yes--germs.
Ewald generally agrees, but he says the establishment is so hypnotized by the watchworks of human genetics that it often overlooks the ever-changing target of germs. He says a Germ Genome Project would do more to explain major illnesses than the lavishly praised human one.
“Not everything is going to be caused by infection,” Ewald says, “but essentially all the big, important ones are going to be caused by infection.”
He has some respected companions in the ranks of germ theorists. They include George Williams, a retired zoologist, former editor of the Quarterly Review of Biology and coauthor of the influential 1995 book, “Why We Get Sick: The New Science of Darwinian Medicine.”
Williams agrees that germs will ultimately help explain the still unknown sources of many major diseases.
“Whether that’s true to the extent Paul is saying, I’m not sure,” he adds. “But it certainly needs to be looked into.”
Right now, no one can be sure, and even some scientists intrigued by Ewald’s theories are wary of his broad claims.
For example, John Hays, a molecular geneticist at Oregon State University, says overwhelming evidence shows a close connection between cancer and mutations of genes that control cell growth. “I don’t see any way to get to the vast majority of cancers without these mutations,” he says.
And cardiologist Paul Ridker, at Brigham and Women’s Hospital in Boston, has searched in vain for germs that could cause cardiovascular disease.
“The critical components of who has a heart attack are acquired: obesity and smoking,” he says. “You don’t necessarily have to invoke exposure to an organism.”
