Let Them Eat Dirt. B. Brett Finlay

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СКАЧАТЬ trained as a scientist, he was one at heart and he soon began to put the oddest things under his rudimentary microscopes: water from a creek, blood, meat, coffee beans, sperm, etc. He methodically wrote everything down and sent his findings to the Royal Society of London, which began publishing his curiosities-filled letters.

      One day in 1683, he decided to scrape the white residue between his teeth and place it under his lens, writing in his notes:

      An unbelievably great company of living animalcules, a-swimming more nimbly than any I had ever seen up to this time. The biggest sort (whereof there were a great plenty) bent their body into curves in going forwards . . . Moreover, the other animalcules were in such enormous numbers, that all the water . . . seemed to be alive . . . All the people living in our United Netherlands are not as many as the living animals that I carry in my mouth this very day.

      Naturally, Leeuwenhoek’s observations of a never-before described world filled with microscopic “animalcules” were met with great skepticism and ridicule. It wasn’t until other British scientists saw it with their own eyes that they began to acknowledge that Leeuwenhoek was not hallucinating. Leeuwenhoek had written many letters to the Society, but discovering microscopic life is what sealed his long-lasting fame. As a result of his many discoveries, Leeuwenhoek is considered the “Father of Microbiology.”

      Still, these findings remained nothing more than curiosities of the natural world, with no real connection to human biology until scientists discovered that those “animalcules” caused diseases. This revelation took place almost two hundred years later, when Robert Koch, Ferdinand Cohn, and Louis Pasteur each separately confirmed that diseases such as rabies and anthrax were caused by microbes. Pasteur’s work also showed that microbes caused the spoilage of milk, and he thus designed the process known as pasteurization, in which microbes are killed with the use of high heat. Milk contamination led Pasteur to the idea that microbes could be prevented from entering the human body, and together with Joseph Lister, they developed the first antiseptic methods. These began to be widely adopted, with one of them still in use today: Listerine.

Avoiding Contagion at Any Cost

      The work of Pasteur, Cohn, Koch, and others led to the widespread knowledge that diseases could be avoided by preventing contact with microbes, and by killing them, and so the quest to eradicate them began in earnest. Health departments opened in London, Paris, New York, and other big cities. Garbage, which had previously been left to pile high on sidewalks, was now collected and disposed of; drinking water was treated; rats and mice were hunted; sewer systems were built; and people with contagious diseases were often placed in isolation. It was through all this that the word “bacteria” gained its bad reputation and inherent connotation of disease, contagion, and plague. Germs were (and still are) entities to be feared, avoided, and fought.

      Fast-forward another two hundred years and an equally astounding discovery is now in progress: in our quest to clean up our world, we have been killing more microbes than necessary and, ironically, this can make us sick. Why? Because our bodies know how to properly develop only in the presence of lots of microbes. This groundbreaking concept significantly expands on what science already knows about the nonharmful bacteria that inhabit our body: that they aid in the digestion of certain foods, and that they fabricate certain essential vitamins. However, only very recently have we begun to comprehend how profoundly necessary microbes are for our normal development and well-being.

Microbes: Partners in Evolution

      The last twenty years of studying microbes has allowed us to understand that microbes aren’t optional forms of life that live within us; they truly constitute part of who we are biologically. To get a better grasp on this, we must first understand that our partnership with microbes is as old as the first species of hominids (our ancestors), and that the evolutionary changes that hominids experienced were accompanied by changes in our microbiota, too. Throughout human history there have been only a few landmark evolutionary bursts (rapid evolutionary changes) that have marked the course of hominids. Interestingly, two of them can be clearly linked to changes in our intestinal physiology and thus with our microbiome.

      As hunters and gatherers (a lifestyle that lasted about 2.5 million years), our ancestors had no permanent homes, living in temporary shelters with few possessions so they could easily move from one place to another. Depending on the geographic region they inhabited, early humans ate different mixtures of meats, roots, tubers, and fruits—whatever was in season. Then an extremely important event occurred that led to one of these evolutionary bursts: our ability to control fire and cook food. We completely take it for granted now, but cooking food made it safer to eat, as heat kills the disease-causing bacteria that thrive in decomposing meat. It also changes the chemistry of the food itself, making it much easier to digest and a lot richer in energy. This sudden increase in energy levels changed everything for humans. No longer did our ancestors have to spend hours chewing raw food in order to extract enough calories to sustain everyday life. Think of what our closest relatives in nature, apes, are almost always doing when see them in the zoo or on TV. If humans hadn’t developed a way to cook food we, too, would have to spend six hours chewing five kilos of raw food every day to get enough energy to survive, just like our primate cousins do.

      The fossil records of humans from this period consist of bones and teeth, making it impossible to determine what type of microbiota lived in the intestines of ancient hunters and gatherers. However, anthropologists have been able to show that the change in lifestyle and diet that resulted from the advent of cooking had anatomical consequences involving the intestines. As energy intake increased, the intestines of our human ancestors shortened and, amazingly, their brains grew, too, increasing in size by about 20 percent. Given what we know today about the link between gut microbes and brain development, it is very likely that intestinal microbiota had a part in this “sudden” brain growth. Brain enlargement improved our capacity to hunt, communicate, and socialize. In other words, cooking made us smarter—it made us human.

      Another evolutionary landmark occurred about eleven thousand years ago. Certain groups of humans realized, probably by chance, that fallen grains from the wild wheat stalks they collected would give rise to more wheat if planted. When humans learned to domesticate plants for food, they tossed away their nomadic ways for a settled lifestyle. Having crops nearby meant that previously small tribes of a few dozen humans could grow to a few hundred, which in turn gave rise to basic traits of civilization, such as trade, written language, and math. If it weren’t for farming, we would all still be picking berry after berry from bushes and walking miles every day. The emergence of agriculture coincides with the appearance of the first cities; inadvertently, agriculture built our modern social structures. This lifestyle change was so successful that farmers replaced foragers, and these days only a handful of people maintain a hunter-gatherer way of life.

      As expected, the lifestyle associated with farming came with major dietary changes. Humans no longer ate small bites throughout the day with the occasional feast after a hunt since farmers had a steady and somewhat predictable supply of foods. So how did this affect our microbiota? By domesticating grains and consequently obtaining most of their daily calories from their new crops, the diet of farmers became less diverse. Based on what is currently known about the microbiota’s response to diet, their microbiota likely became less diverse, too. In fact, comparing the intestinal microbiota of the Hazda people of Tanzania, one of the few contemporary tribes that relies on foraging, to a modern farmer is like comparing a rain forest to a desert, in terms of biodiversity. Less diversity in our microbiota is associated with a number of human diseases, many of which we cover in later chapters.

      Although farming has been around for only eleven thousand years (just 0.004 percent of human history!), physiological changes have also been linked to the agricultural diet, and some of these changes involve our resident microbes. The new diet brought with it cavities and other periodontal diseases, mediated by bacteria rarely found in foragers. Our teeth, jaws, and faces have grown smaller, too, probably because chewing was reduced on such a diet. Some evolutionary biologists believe СКАЧАТЬ