"Plague Time" has been the subject of much media attention, including an article in Newsweek which reffered to Ewald as a "a bold-minded evolutionist … who has created a whole new framework for thinking about infectious disease."
"The major uncertainty," Ewald writes, "is just how many infectious plagues are smoldering along, consuming the oblivious-those people who think that their bodies are just falling apart from the wear and tear of life."
"It is a very controversial idea, and not yet widely accepted," said Professor of Biology Patrick Williamson. "But it is important to remember that this idea is a general proposition that can be applied to many diseases but cannot be proved all at once. It can only be accepted or rejected for one disease at a time, and for each individual disease it is a controversial proposition that will be attacked and supported."
"All those arguments will take time, so that it is not an idea that will be either accepted or rejected all at once, and it is also unlikely to be accepted or rejected soon," Williamson added.
Genes
"Plague Time" employs evolutionary arguments to explain why germs, and not genetics or lifestyle factors, are primarily responsible for certain diseases.
Though it might seem obvious that diseases which affect people when they are young or of child-bearing age have a negative impact on their ability to reproduce, that does not mean that the same should hold for older people. If a sixty-year-old who stopped having children were to develop Alzheimer's disease, it is not clear if his condition would affect his offspring's ability to survive and reproduce, even if the disease was genetic.
Scientists have used similar arguments, focusing on the fact that certain diseases affect only older people, to justify a genetic theory of Alzheimer's disease. "I think this has continually confused medical people," Ewald said. "The confusion arises because the people who make this claim do not realize that harmful characteristics of people in their older age will not be winnowed out by natural selection."
Older people serve important evolutionary functions by guiding, teaching and caring for youth, according to Ewald. "The functions would also include helping their adult offspring," Ewald said. "This could be very important at times when these adult offspring are incapacitated, for example, when caring for or taking over the role of parents if the parent were knocked out of commission [for example,] by a broken leg or by illness."
It is possible, Ewald said, that menopause might be the body's way of telling women that the reproductive part of their lives had concluded, and a phase focusing on caring for and educating the young has begun.
Germs
Ewald believes that the medical community, for the most part, has been searching for the origins of disease in the wrong places. Instead of searching for infectious causes, Ewald said, many scientists have used genetics and lifestyle factors as a "rug to sweep [various diseases] under." Ewald believes Alzheimer's disease is just one of many that falls into this category.
Though Plague Time ascribes primary responsibility for certain chronic diseases to infection, it accepts that both genetics and lifestyle factors can aid an infection. It has been relatively easy to link disease to the wrong sources, Ewald said, because infections work differently than genes.
Germs can last for incredibly long periods of time inside of the body's cells without causing major damage.
Ewald is careful to explain, however, that finding a causal link between infection and disease is no easy task. "Although modern medicine can recognize some of these enemies, it has only a few clues about most of the others," he writes.
The easiest way to identify an infectious disease is to analyze its transmission patterns. Diseases like chicken pox, which are clearly transmitted by human contact, are obvious candidates for infectious diseases.
Modern medicine, Ewald said, has identified the most obvious of the infectious diseases, but it has not been able to do the same for more subtle diseases. This is because all but the most basic transmission patterns are incredibly hard to map.
If chicken pox germs were acquired at age ten but did not manifest themselves until age sixty, scientists might need fifty years before they could to prove that chicken pox had infectious causes. "If one were to rigorously apply Koch's postulates [which describe how to identify an infectious disease], at least 50 years would be necessary," Ewald said, "unless the researchers felt confident in using an animal model in which a similar disease manifested itself in a shorter time."
Ewald points to peptic ulcers and cervical cancer as examples of infectious diseases that were mistakenly attributed to genes and lifestyle factors.
In the 1980s scientists believed that peptic ulcers were genetic or caused by smoking, spicy foods and stress. Since it was discovered that bacteria were responsible, ulcers have been treated with antibiotics. Though it was also known for years that a correlation existed between cervical cancer and number of sexual partners, only recently has it been shown that human papilloma viruses are the causal agent. They have been found in over 90 percent of cervical tumors.
Evidence also exists that suggests genes are not primarily responsible for breast cancer. If the disease was genetic, a high percentage of identical twins, who share the same genetic makeup, would both be expected to get it. Studies show, however, that in 80 to 90 percent of female identical twins over the age of 30, one gets the disease while the other does not.
Prevention
To combat germs, Ewald writes, antibiotics will not prove as useful as they might appear. Because germs mutate so quickly, they are able to develop antibiotic resistance in relatively short time periods.
Ewald's solution for preventing the most dangerous germs from getting into the body focuses on various strategies, including cleaning up water supplies and using mosquito nets to prevent diseases like cholera and malaria. "The argument doesn't rely on the overall prevention of entrance of germs; rather, it relies on the selective prevention of the harmful variants of the germ," he said. "If one cleans up the water supply, the remaining routes of transmission rely on host mobility."
Cleaning up the water supply would kill the most harmful germs, and evolutionary factors would force those that had already infected people into a no-win situation.
This is because the most harmful variants tend to render people immobile, often preventing them from contact with other people. The germs are then faced with a decision: kill the host (and themselves die) or evolve to a more gentle variant. "The result is that the mild strain will win the competition and the population of germs as a whole will evolve toward reduced virulence," Ewald said.
Though medicine has made great strides since it was discovered that water could harbor disease, Ewald argues that there is still much to be done. Scientists must accept that infection is responsible for many more diseases than they had previously thought. They should understand the evolutionary implications of infectious diseases and employ strategies for curtailing infections. Ewald believes that if these steps are taken, "humanity may achieve health benefits as remarkable as anything that has been obtained throughout the history of medicine."
"Modern medicine is not nearly as far advanced as the textbooks and most physicians would have us believe," Ewald writes. "It is now more important than ever to identify the weaknesses and mistakes of our medical establishment, not for the purpose of attacking hard-working doctors, but rather to suggest ways to better understand the predicament we are in and the range of options that we have at our disposal for overcoming the very present danger we face."