Are we psychologically prepared to fight epidemics? Has evolution prepared us for such events? Yes and no. Evolutionary psychologist Douglas Kenrick — about the causes of death of Homo Sapiens, wild tribes, the behavioral immune system and internal contradictions.
Mankind as a species has existed for many centuries, and many misfortunes have fallen to its lot, including epidemics. Is our psyche adapted to such diseases and the fight against them? The answer to this question is offered by Professor Douglas Kenrick, an expert in the field of evolutionary psychology, the author of many books on the social and evolutionary psychology of people.
Why did our ancestors die?
If we compare us with previous generations, then in a relatively short time, radical changes have occurred in the causes of death. Over the past 150 years, the chances of people dying from an infectious disease have dropped dramatically. This applies mainly to the population of richer countries, but in general it applies to almost the whole world.
The New England Journal of Medicine published an article comparing causes of death in 1900 and 2010. The leading cause in 1900 was “pneumonia or influenza” — more people died from it than from heart disease in 2010. Tuberculosis killed more people in the early XNUMXth century than cancer does today.
If you add gastrointestinal infections and diphtheria to pneumonia and influenza, these infectious diseases killed as many people in 1900 as they did in 2010—all diseases that rank in the top ten causes of death. This includes coronary heart disease, stroke, chronic obstructive pulmonary disease, lower respiratory infections, Alzheimer’s disease, cancer, diabetes, car accidents and others.
In fact, Kenrick explains, in 2010 only one category of infectious diseases made it into the top ten—pneumonia or influenza—but the overall mortality for that category was 12 times less than in 1900. From the point of view of science, 1900 is not an evolutionary past, because it was only 3-4 generations ago.
What did our more distant hunter-gatherer ancestors die from? Agriculture, the scientist specifies, appeared only 10 thousand years ago. The remaining 90% of its history, mankind was engaged in just hunting and gathering. Based on archaeological and genetic data, researchers suggest that Homo Sapiens in its more or less modern form has existed for about 200 thousand years. And in fact, we can very conditionally say that agriculture began to develop about 10 thousand years ago. Most of our ancestors started doing it only about 5 thousand years ago. Therefore, speaking about the evolutionary past of mankind, we have in mind mainly the tribes of hunters and gatherers.
The biggest difference between the statistics of modern people and our distant ancestors is in the level of infant and child mortality.
Obviously, Professor Kenrick ironically, that in those days, no CDC collected statistics on the causes of death. However, archaeologists, anthropologists and demographers have come up with clever ways to solve this problem. One of the methods involves the excavation and study of ancient burials, followed by analysis of the bones. This allows you to determine the age of people at the time of death.
Another method involves the analysis of information about the tribes of hunters and gatherers who lived on our planet in the past and the century before last, and the search for analogies in the causes of their death with groups that lived in similar conditions millennia ago — for example, in the Australian deserts, on the African plains or in South American jungle. These groups, in turn, were compared with those that led a horticultural lifestyle — a stage halfway from hunting and gathering to agriculture; and also with groups that have only recently come into contact with Western civilization.
University of Arizona anthropologist Kim Hill and a group of other eminent scientists have even compared the mortality rates of modern hunter-gatherers and wild and captive chimpanzees. The same group of scientists conducted a study of 722 deaths among the Guajibo Indians of Venezuela, who continued to lead a life of hunter-gatherers until the end of the XNUMXth century.
Based on extensive interviews with representatives of this people, Hill and his colleagues divided the deaths into those that occurred before and after contact with Westerners. It turned out that in the past, guajibos had predominantly died from slaughter as a result of conflicts related to competition for women and revenge, as well as from accidents caused by the life of hunter-gatherers.
Scholar Barry Hewlett published a report on mortality rates among African nomadic Aka Pygmies. The homicide rate is lower there, but the death rate from lifestyle-related accidents is just as high. For example, people fell from trees trying to get honey or palm nuts, were trampled by elephants, or died from the horns of rushing antelopes. Similar accidents Kenrick compares with modern mortality in car accidents.
The biggest difference between the statistics of modern people and our distant ancestors is in the level of infant and child mortality. Obviously it is much lower now. Another big difference is that very few hunter-gatherers died of heart disease or cancer. According to the scientist, the lack of cardiovascular disease is likely due to the fact that hunter-gatherers did not suffer from obesity, thanks to a certain diet and an active lifestyle. The second may be due to the much lower exposure to chemical toxins, which are carcinogens.
As for life expectancy, it cannot be said that it was low for all our ancestors. Researchers Michael Gurwen and Hillard Kaplan combined data from a number of studies and found that a significant percentage of people who survived adolescence could live into their 50s and beyond. And those guajibos and akas who reached old age died of infectious diseases, not heart disease.
So has our genetic makeup prepared us to fight the modern pandemic? Researcher Mark Schaller and his former students Damien Murray and Justin Park have written extensively about what they called the «behavioral immune system.»
The essence, according to Kenrick’s explanation, is as follows. The skin and mucous membranes keep out some of the hungry parasites that try to enter our bodies, but not all. As soon as a pathogen enters the human body, other mechanisms come into play to prevent it from becoming fixed — in particular, our white blood cells, leukocytes. But we can’t put up a total resistance to every new bacterium, so the best defense is infection-prevention behavior.
Schaller, his colleagues and other scientists have found evidence that people who are usually worried about the possibility of infection tend to avoid contact with strangers. And residents of places where there are a lot of pathogenic microorganisms are much less open to social contacts with strangers.
Many of the diseases that caused the death of our ancestors were introduced into their bodies from the soil, with water, or through the animals they hunted. And even in today’s world, diseases such as the flu, although they often occur in distant exotic places, are usually transmitted to us not from strangers, but from someone in our close circle of contacts.
Do not take a plane to a distant exotic place? Easily! Sit in your room and not go to visit relatives? Difficult!
Even avoiding strangers, our ancestors could not avoid communicating with those who were nearby, because they lived in small villages with a high population density, sharing food, tools and living quarters.
Moreover, hunter-gatherers have gained tremendous survival advantages by sticking together, taking care of each other «in sickness and in health.» This was documented by Kim Hill and his colleagues. Therefore, it should not be surprising that even when we are concerned about the possibility of infection, we do not have special skills to maintain social distance from members of our own groups.
“Don’t get on a plane to a far exotic place? Easily! Sitting in your room and not going to visit relatives and close friends? Difficult!» writes Professor Kenrick.
This does not mean that social distancing cannot be a good strategy during the current epidemic. It just means that keeping social distance for us is like “not eating chocolate” or “reading in a foreign language.” It doesn’t come naturally, and we need self-discipline to implement such a strategy.
Professor Douglas Kenrick shared his opinion with some of the scientists mentioned in it, who gave their comments.
Kim Hill, an anthropologist at the University of Arizona: “Respiratory infections have been the leading cause of death in almost every human tribal community for which we have demographic data, even if it was small. Zoonotic diseases were extremely common in our past — every day, hunters came into contact with the blood of wild animals. But the infections were mostly local, and then quickly faded due to the isolation of individual residential units, groups.”
“By the way, zoonotic diseases are diseases that originated in other species, like the coronavirus that humanity is currently dealing with,” adds Kenrick.
Mark Schaller, professor of psychology at the University of British Columbia and author of articles on the behavioral immune system: “There is another problem in which simple physical distancing recommendations do not work as well as more stringent measures.
The point is the discrepancy between the epidemiological reasons for the need for physical distancing and the more intuitive justifications for it. The epidemiological argument for why I need to distance myself from others is not only that it will help me not get infected myself, but that it may prevent me from infecting someone else!
This is very important because, as we know, a person can be contagious without knowing it. But intuitively the mind does not accept this. Perhaps we could develop a behavioral immune system based on an intuitive desire to protect ourselves. But I don’t think we’re going to have an intuitive psychology based on an inner drive to keep people away from us who we might infect.»
A lot of self-control and responsibility is required of us to comply with such security measures.
According to scientists, for many millennia, mankind has encountered pathogenic bacteria and viruses that pose a serious threat to life. But the peculiarities of living in closed communities and the desire to distance themselves from strangers often kept the spread of the disease within individual settlements.
Today, when we are actively moving around countries and continents, it turned out to be too easy to bring a disease from an exotic country and spread it around the world. And our instincts and natural habit of close contact with family and friends, as well as the general population density in cities, in this case contributed to the development of the pandemic.
It is likely that in order to stop the virus, humanity needs a «behavioral immune system», including temporary physical distancing from people in close circle of communication. And because it conflicts with intuitive human behavior, a lot of self-control and responsibility is required of us to comply with such security measures.
About the Author: Douglas Kenrick is an evolutionary psychologist and author of Instincts and the Meaning of Life. Why are there so many animals in us” (Peter, 2017) and other books and publications on the evolution of human behavior.