Altruism, Infectious Disease, and the Future

This essay should be of great interest during the coronavirus pandemic. But I wrote it before the pandemic began, based on reading a book written in 1965.

I first discovered the scientific principles of the evolution of disease by reading the René Dubos classic Man Adapting. Even though I was a professor, I still had never heard of balanced pathogenicity. And it was even later that I began to read some of the many wonderful books about altruism. But it was only recently that I noticed the connection between the two.

Altruism has evolved by at least three mechanisms: kin selection, and direct and indirect reciprocity. Kin selection (Blood is thicker than water) is widespread in animal societies, and direct reciprocity (Let’s help each other) is common among intelligent animals. Indirect reciprocity (A good reputation is worth more than money in the bank) is nearly absent outside of human society.

In human tribal societies, altruism was extremely important. The best way, perhaps the only way, for a person to rise to the top was with help from friends and supporters (direct reciprocity), and with a good reputation (indirect reciprocity). Trustworthiness was rewarded, and cheaters were hated. At least one scientist, Robin Dunbar, speculated that human language evolved largely as a facilitation of reciprocity.

Balanced pathogenicity is where a virulent disease, so long as it is transmitted by direct contact, usually evolves into a milder form over time. This is because even in prehistoric times everyone around the victim knew that the victim was sick—whether from demons or bad air—and stayed away from him or her. A successful germ was one that had mild effects on the victim, who could then get up out of bed and go around spreading the germs. In this way, an acute disease can evolve into a chronic disease or even all the way to commensalism: Dubos speculated that some diseases evolved themselves out of recognized existence. This has been my experience. Like many people who grew up in Tulare County, California, I had tularemia. I did not know it, however, until a skin test revealed it. The doctor told me I had just felt bad one day, and that was it. In earlier decades, it was often a serious ailment.

The first parallel between altruism and the transmission of infectious disease is this. Just as everyone knows who it is that has an acute disease, everyone knows whom you can trust and whom you cannot, in traditional society.

Today, however, massive corporations conduct much of their business in a way that their practices are shielded from public scrutiny. Even corporations that had infamous practices, as many did during the 2008 recession, remain in business and are profitable, since most customers nationwide do not remember what they did. Reciprocity and reputation have not eliminated them or even, in some cases, reformed them. In modern corporations, oppressive decisions are made in boardrooms, decisions that a CEO might not normally make if he actually looked the customer in the eye.

The second parallel between altruism and infectious disease is this. There are many diseases in which balanced reciprocity does not evolve. Cholera is an example. Potential victims cannot know where the cholera germs in the water came from. Did they come from an acutely sick, or a mildly sick, person? Virulent and mild germs spread equally well. This is how Paul Ewald succeeded in getting cholera to evolve into milder form in some locations: if cholera could not spread through water, it had to spread through direct contact, and by doing so it evolved into a milder form.

In the mass of online information about corporations, a customer is unlikely to be able to determine which banks, for example, have a good reputation and which ones have a bad one. They choose banks the way people drink contaminated water. I certainly did, and regret it.

It can get worse. Some diseases spread more effectively if their victim is very ill. This is often the case with diseases that spread by insect vectors. Mosquitoes prefer to bite victims who are too sick to move around or to swat them. Such diseases can evolve to become worse.

In a similar fashion, some corporations actually benefit from social disruption that they and other corporations create. Consumers who are suffering from inadequate sleep, debt, and job insecurity seek pleasures and entertainment that many corporations are only too happy to provide to them.

In traditional societies, anti-altruistic people were ineffective for the same reason that virulent diseases were. But in modern societies, anti-altruistic corporations can equal the profitability of altruistic ones, the same way cholera spreads, or even exceed the profitability of altruists, the same way that insect-transmitted diseases spread.

If I am right about this, altruism faces significant challenges in the immediate future, even after the current pandemic abates.

This may be no more than an analogy. If so, it is a useful concept for teaching the principles of evolution—principles that show up in such seemingly unrelated fields as epidemiology and altruism. As a result, students may be forced to realize that they cannot consign evolution into an easily-ignored little box in the warehouse of knowledge.

Thinking Back on René Dubos: Ecological and Evolutionary Medicine

For many years, I have been teaching a subject in general biology classes that I call the Ecology and Evolution of Disease. It includes the subject that is now called Evolutionary Medicine (it now even has its own journal). I continue to be amazed that no general biology textbooks seem to mention it.

I grew up thinking what most people still think about health and contagious disease. As Ogden Nash wrote, “A mighty creature is the germ, though smaller than the pachyderm...” It was all very simple. Germs caused contagious diseases. The solution was to kill the germs. Problem solved.

But it is not so simple, and the book that opened my eyes to the real complexity of health and disease was Man Adapting, a 1965 book by René Dubos. It was an old book when I first read it in the late 1980s. It was ahead of its time, and maybe still is.

Dubos’s main point was that health is a creative response. It is delimited by biology and evolution but it is highly personal. That is, a disease can take a different course in different individuals. Dubos said that, when we ask what man is, we should not be satisfied with the answer that he was an ape. Instead, we should think of ourselves as ecosystems in which health is the result of the proper balance of all of our physiological processes, as well as all the microbial species that call our bodies home.

Dubos wrote about how the human body is an integrated whole, and conditions of the body can alter the course of disease. For example, stress can affect the immune system, with the result that bacteria that are already present but unnoticed can flare up into disease. This is now well known. The stress of viral disease can make a person susceptible to bacterial infections such as sinusitis and pneumonia, caused by “germs” that were already present. The stress of allergies caused me recently to have severe sinusitis. We have all seen examples of people who, from stress and its related habits such as smoking, seem to always be sick. Also, Dubos may have been one of the first scientists to write extensively about how an upset to biological rhythms can result in disease, including infections.

And the effects of stress can pass on from one generation to another. A mother animal who experiences stress can have behaviorally abnormal offspring, and it might result in part from the effects of stress on the prenatal environment of the fetus.

Dubos also included a lot of information about how Old World diseases killed up to 90 percent of many Native American and Polynesian populations, because they had never evolved resistance to these germs. Why didn’t the Europeans die of New World diseases? Because there weren’t very many. America was populated by immigrants from Siberia, and Polynesia by people sailing long distances in boats. Only healthy people could have made those journeys. This opened my eyes to a whole new understanding of some parts of human history. After Dubos, many historians have written about this.

An important, and still often ignored, aspect of our body ecosystem is its microbial inhabitants. Gnotobiotic animals (born, raised, and maintained in totally sterile conditions) are abnormal. Their organs develop abnormally, and so do their immune systems. They heal more slowly from injuries.

Many parts of our bodies, especially the skin and digestive tract, harbor trillions of bacteria, most of which are harmless, and some of which are beneficial. Some of the beneficial ones produce molecules which, to them, are wastes, but to us are vitamins, especially B vitamins. In our intestines, the lactobacilli and bacteroides are beneficial, while bacteria such as the famous E. coli are usually harmless. E. coli just seem to be along for the ride. In rodent colonies with normal intestinal bacteria, kept in total isolation from the outside environment and other rodents, the E. coli gradually disappear, leaving the lactobacilli and bacteroides to dominate. But even the merely non-harmful bacteria can do us some favors by crowding out the pathogenic bacteria.

This is the ecology of disease within a human body. (There is also the ecology whereby bacteria spread from one host to another.) But evolution also plays a role. This was the book where I first read about how many disease organisms have evolved to become less virulent. For example, many diseases, such as smallpox, leprosy, and (a disease Dubos and his wife studied) tuberculosis became less and less deadly over the course of many decades even before the introduction of antibiotics and antiviral therapy. Some infectious diseases have pretty much evolved themselves out of existence. One example is the English sweating sickness, which was a severe plague from 1485 to 1551. Its main symptom was profuse sweating. Then it vanished. Perhaps, Dubos speculated, it evolved into such a mild form that nobody noticed it after 1551.

I knew he was right as soon as I read his book, because I could think of my own stories. I had read many gruesome stories about smallpox. But my own grandmother had smallpox. For her, it was a severe but not deadly disease, and did not leave pock marks when she recovered. She had become infected with a relatively mild strain of smallpox. Before the WHO began its campaign of worldwide vaccination to eradicate it, smallpox was already on its way out. I also knew this from direct experience. I grew up in Tulare County, California, after which the disease tularemia is named. It is endemic to the area, and probably everyone who lived there had gotten it. Only, for us in the twentieth century, it was a mild disease that we mistook for the flu. I did not know I had had it until I tested positive for tularemia antibodies when I was a teenager.

How can a disease evolve to become milder? The simplest explanation is that a horrible germ that quickly kills its host cannot easily spread to a new host after it kills the first host. The first host is too sick to get up and spread germs around, and everybody stays away from him if he tries. Also, some people are naturally immune to the disease, and they are the ones who survive the most often. But the main reason is that the mild germs are the ones that are successful at spreading to new hosts.

This is the evolutionary process of balanced pathogenicity. It was scientifically demonstrated by a study on a rabbit virus, myxomatosis, in Australia in the 1960s. The rabbit populations evolved resistance to the virus, and the virus populations evolved into a milder form.

I got the impression from reading Man Adapting that balanced pathogenicity was true of all infectious diseases. Of course, it is not. Cholera has not evolved into milder form, because you get it from drinking contaminated water—water that has been contaminated by very sick, or by mildly sick, people. You cannot avoid the bad germs of the very sick people, mixed in as they are with the mild germs of the mildly sick people. Also, malaria may evolve to become worse, because mosquitoes like to bite sick people who cannot shoo them away, rather than alert people who are busy. (However, Dubos pointed out, a person who is very sick from malaria will die sooner, such that the mosquitoes might bite the mildly sick people more often simply because there are more of them.)

It was this book, Man Adapting, that changed many of my views of science, making them less linear and more holistic.

Balanced Pathogenicity in Shangri-La

When I first learned about balanced pathogenicity back in the 1980s, it made me feel good about the world. This is the process in which germs evolve into milder forms over time. Natural selection favors the milder strains of germs because they can spread more readily. Any germ that kills its host is at a disadvantage. There are many examples in which diseases used to be very virulent, but today they are milder even without vaccination or medication. Examples include smallpox, which in Europe and North America evolved into a mild disease; leprosy, which today is a slow skin disease but used to kill people quickly. There are even diseases such as the “sweating sickness” that had major outbreaks in Europe in past centuries but appears to have evolved itself out of existence (it persists only in very mild forms): there are no diseases today that have exactly those symptoms. Balanced pathogenicity was part of the balance of nature in a blessed world.

Or so I thought. That’s what I wanted to believe.

Then I started learning about the exceptions. Waterborne diseases such as cholera do not evolve into milder forms. Insect-borne diseases may evolve into even worse forms. So I had to change what I taught and wrote: balanced pathogenicity applies to diseases that spread to a new host by close proximity to the victim. My main example was ebola, which, I thought, will evolve into a milder form since the worst forms of it keep healthy people from coming in close proximity to the victims.

But it turns out that even ebola can evolve into a worse form, as explained in this article by Carl Zimmer. I suppose that this evolution of worse forms of ebola is a temporary reversal of the overall trend of balanced pathogenicity. But I am now having to make so many “exceptions to the rule” that I am beginning to wonder how much of a pattern balanced pathogenicity really is.

My original feeling about balanced pathogenicity came about because I wanted to believe that there was a fundamental goodness to the world. Bad things happen, but within them is the seed of a better world. This was partly because I got my optimism from the same source that I got my original information: Rene Dubos. I learned about balanced pathogenicity by reading his Man Adapting and Celebrations of Life. He was a scientist and informal philosopher in the same mold as Lewis Thomas. A great thinker. But his “gospel” was that evolution ultimately produces a better world. I wanted very badly to believe that evolution was a good process that God incorporated into a good world. But the world in which evolution works for the Greater Good is more of a Shangri-La than a real world.

Balanced pathogenicity happens, except when it doesn’t. Evolution makes the world better, except when it doesn’t. Creationists look for scientific reasons to believe God is good. Theistic evolutionists look for scientific reasons to believe that evolution produces goodness that God intended. In this particular sense, I am not sure that theistic evolution is much of an improvement over creationism.