As a tyke I was a walking ad for a detergent commercial. Like many little boys I was a magnet for grime, mud, muck, dust —- you name it. My mother, young, inexperienced and perhaps a touch anxious, would become alarmed when I plowed into unsterile environments only to be reproached by her mother to leave me alone because I needed “to eat 2 pounds of dirt in order to be healthy.” As it turns out Grandma, God rest her soul, may have been onto something.
Today, I smile when I think of this bit of nostalgic lore but I also wonder at the magisterial complexity of life on this planet. That might seem quite a leap, but it’s really only a small step in considering how our species, sometimes in unsearchable ways, has interacted with organisms both visible and invisible that surround and shape what we have become and who we are today.
Indeed, speculation is rife with how our early ancestors became implicated with their environment. Human biology and the ecosystems of nature are knotted together with such labyrinthine complexity that even today the relationships are not fully understood. Some conclusions seem self-evident: The virtual hairlessness of modern Homo Sapiens compared to their even more hirsute ancestors, much less other mammals, unmistakably indicates that early humans were compelled to gravitate to warmer as opposed to arctic temperatures. Conversely, tropical rain forests, factories for the most protean and diverse forms of life, were left unsubdued by our race, at least until very recently, because deadly micro-parasites that cannot survive sub-freezing temperatures or low humidity thrived in that sultry habitat.
So human beings migrated to more congenial climes both in Africa and later Asia. Parasitism existed there also, but not in the same quantities or toxicity. Micro-parasites are slow to advance and as a countervailing measure a highly evolved natural balance materialized between these parasites and rival parasites. This development gave our species a fighting chance to survive disease and extinction. As a result, our human and proto-human ancestors, while by no means living to the Bible’s allotted “Three score and ten” nonetheless lived tolerably healthy lives for reasons not least of which was that their immunological resistance was fortified by being immersed in the mud, the grime, the dirt and the muck of their surroundings.
In time, that 3-pound mass between our ears asserted itself and technology intruded upon human affairs, changing life on earth in ways that are almost incalculable. Humans soon became capable of fashioning weapons that could kill large bodied herbivores that heavily populated both the African and Asian savannas. Bereft of the massive musculature body, sharp teeth and claws of the apes, the genus homus had to rely on the superiority of their cognitive and communications skills to overcome the impediments of nature (hunting, for example, provided clothing as a unique cultural adaptation for protection against the harsher elements of existence) as well as a means to enlarge their food supply.
This adaptability proved especially useful with the ebbing of the last Ice Age, some 12,000 years ago, where in virtually every part of the world Homo Sapiens showed astonishing versatility in coping with cataclysmic climatic and geographical upheavals that traumatized our planet. Even more crucial was that the hunting and gathering economy which sustained human life since time immemorial was being replaced by a developing agriculture that was slowly but inexorably sweeping over the environs of North Africa, Asia and Europe. A narrative on how the farming revolution exactly materialized remains beyond our historical understanding except in the most generalized terms. Still, the Ice Age, in creating new river valleys, coastal inlets and fertile crescents of land, became such a game changer that the entire material fabric of what would become modern civilization began to congeal.
The essentials of this new epoch were the growing of crops and the practice of animal husbandry. Populations not only became larger and lived in smaller areas, but for the first time settlements, some of which would turn into cities, became robust as a result of the unprecedented surplus of food. Social organization became more defined and vital, only because the idea of social order, law and custom became all the more relevant and necessary. But the felicific calculus that resulted from the farming revolution was not a zero sum game. While there was a greater solidity in terms of settlement, populations became more sessile as mass peregrinations became less prevalent. Settlements became not only more exposed to human waste but also to animals and animal waste. Meanwhile, these communities had to rely on the same water source for all their needs, making the prospect of contamination greater. These living environments provided an ideal vehicle for intestinal parasites to move from one host to another thus threatening these populations in a way they never did their hunting and migratory predecessors. Animal diseases would become human diseases: Measles derived from canine distemper, as did rabies; smallpox from cowpox; influenza from hogs; yellow fever from monkeys; bubonic plague from rodents. The grazing of large numbers of cattle and sheep resulted in various bacterial and viral infections that could easily become endemic. Even the modern plague of AIDS most likely had its provenance in the animal kingdom.
The perplexing thing is why a particular organism becomes a pervasive killer while others are either engulfed by white corpuscles, a first line of defense, or are killed off by other mechanisms such as an organism’s antibodies, which are manufactured when being attacked. So human ingenuity and adaptability has its downside; yet because of the advancement of culture and the pooling of experience the collective benefits of social organization, despite parasitic infiltration, human population density in these settlements became 10-20 times greater than hunting densities. Human ingenuity triumphed as did human biology, which again developed a resistance to many of these viral infections by being exposed to them by virtue of living in the muck, mud and grime of daily existence.
This is not to say that viral infections have not decimated populations and even great civilizations. They have. A 2nd-century outbreak of smallpox had a devastating impact on the Roman Empire and was probably the first in a series of blows that led to its downfall. Cortez had but 600 men in Mexico, yet they conquered millions of Aztecs and their extraordinary civilization. Pizarro, in the same fashion, conquered millions in the Inca civilization in South America. The historian William H. McNeill persuasively argued that it was disease that the Amerindians had no resistance to, convincing them that the God of the Conquistadores was far more powerful despite their extraordinary numerical advantage. The Black Death of the 14th century did much to undermine institutional Roman Catholicism slowly paving the way to Luther’s Reformation. In modern times the outbreak of the Great Influenza of 1918, the last year of WWI, killed at least five times as many as the war did. The one-two punch leveled society in the succeeding decades and may well have served as a contributing factor to the rise of Fascism and Totalitarianism.
Yet, infections that had once threatened the lives of our ancestors —- tuberculosis, cholera, malaria, smallpox —- are no longer to be dreaded, but in a fascinating new book “An Epidemic of Absence, Moises Velasquez states that diseases such as typhoid, mumps, rubella, yellow fever etc. no longer trouble us because of the science of immunization. But before we unlock the liquor cabinet and uncork a bottle of champagne, there is now a list of modern illnesses that our ancestors hardly knew: asthma, eczema, hay fever, diabetes, multiple sclerosis, rheumatoid arthritis. According to Valasquez and others, while modern hygiene prevents infection, it also promotes allergy and autoimmunity. Infection with parasites, says Valasquez, prevents or ameliorates many diseases (like those just previously listed) or inflammation. Studies show that Finns isolated in an impoverished Soviet province had more parasites and fewer allergies than Finns in Finland. Swedes in immaculate Stockholm had three times as much asthma as Estonians in smoky Estonia. Ethiopians got allergies when they lost their intestinal worms, and counter-intuitively, living on a farm greatly reduces the possibility of developing allergies. Valasquez cured his own hay fever by infecting himself with hookworms before deciding the payoff of diarrhea was too great.
Ever wonder about the increase in cases of autism that some scientists believe is the product of overdiagnosis? Valasquez convincingly argues that this disorder parallels asthma in its recent rise among affluent, urban, mostly male, disproportionately firstborn people. Valasquez says that the brains of people with autism are often inflamed and infection with worms and viruses can powerfully modify autistic symptoms. Valasquez theorizes that our immune system evolved to expect parasites. In a world with no parasites the immune system becomes unbalanced. Valasquez speculates that even heart disease, diabetes, obesity, depression are related to an unbalanced immune system caused by an impoverished microbial ecosystem —- meaning we’re not playing in enough dirt. Science writer Matt Ridley reflecting on these facts states that “dirtier lives may be just the medicine we need.” Yes, Grandma would agree, you need to eat 2 pounds of dirt in order to be healthy.