We work to serve the microbes
Precis of Dirt is Good (2017) by Jack Gilbert, Rob Knight, and Sandra Blakeslee
This is a repetitive book written for new parents of the upper middle class. It takes fascinating science with a transformative understanding of what it is to be human and answers redundant questions about babies, dogs, diapers, and birth. I read this book to better understand Sandra Blakeslee’s effect on popular understanding of science, because she is possibly the most respected popular science writer in America today. She is really good at making nice sentences that are easy to read and I bet she helped get this project off the ground, which is admirable in itself. Emotionally, this book is much better reading than the relevant wikipedia pages, even if the content is about as rich. I blame the publisher for the awful focus on babies, classist myopia, and the total omission of more interesting topics such as sex and Komodo dragons.
The core idea is amazing. Humans, like all multicellular life forms, are vehicles for microbes who were here before us, helped bring us into existence, live inside us now, and are happy to eat us when we die. The human experience is about as important to them as broiler chicken experience is to us. Focusing on microbes lets us better understand humans.
The human body is full of microbes, with about 30% more microbe cells than human ones, and relies on microbes for many basic life processes. Mice can live without microbes, thouogh they are extremely vulnerable when released from their sterile environment. Aphids and termites actually can’t live without their microbial symbiotes, though they used to be able to! They came to rely on microbes more over the millennia, which sounds awesome and is something I want also.
Life on earth probably began in deep sea vents, where chemotrophs extracted energy from the weird chemicals and heat, or when a microbe landed from space — in a comet carrying water or just slowly falling down from the great beyond. Those are just some facts they mention. Anyway, doesn’t make much difference — single cellular organisms precede multi-cellular life and so have always had uses for it and a role in its existence.
Microbes have been at war with viruses for a very long time, developing countermeasures and tactics to destroy each other. Microbes also compete with each other sometimes, and are the basis for most antibiotics. The immune system, as you can imagine, is hilariously corrupted by microbes and never existed to keep us germ free, just to keep the human part alive while it hosted all the microbial revelers.
This is awesome and, yet, all this is presented in a very short chapter before we delve into somewhat sketchy baby advice.
When I was young, I imagined that, if there are bugs that make you sick, there could be bugs that make you stronger! Where were these bugs? It turns out they were already there, in my body, blocking out more malicious bugs (or, let us call them less enjoyable partners in the game of life), helping me digest food, regulating my emotions, and probably doing a bunch of other stuff we still don’t know about. The science is still quite new on this whole topic!
Now, I’m going to cherry pick from the rest of the book because it presents information very poorly, from my point of view.
The microbes in one area, such as your gut, form an ecosystem, which the authors compare to a rainforest. Some microbes produce things others eat, some eat each other, some like one niche or prefer another. As this ecosystem is inside you, you are its environment and it can have an impact on you. Some gut microbiomes are correlated with obesity, autism, or other disorders. In particular, you can transfer microbes from one gut to another and make a lean mouse obese or obese mouse lean! Fecal matter transplants are not well understood for humans but are promising.
Generally, human microbiomes are fairly stable. One study found that 70% of humans studied had a stable microbiome over one year; 60% were stable over five years. So, we can trust the microbiome to remain stable after punctuated exposures or severe conditions, but we can also expect it to change over the years. I think this is part of the reason that exposure to microbes seems like no big deal to the authors: it’s quite unlikely that the flu virus will shift your microbiome long term. (On the other hand, I wonder if the authors care that, when a human gets the flu, it is really unpleasant for a few days and death is possible. It also sounds to me like, 30% of the time, your microbiome will shift within the year! Which makes it pretty common.)
Buildings can have microbiomes too, and the microbes in farm homes seems to help kids grow up without asthma or major allergies. The evidence for this comes largely from Amish vs Hutterite homes, where the lifestyle is similar but one lives on the farm and other commutes. A related effect seems to exist between Finnish homes and Russian homes across the border, but the key difference is poverty not animals. Less hygiene, less control, and less isolation all helped the Russian kids get less serious ailments. The microbes in the Russian kids were more diverse, which helped. There are probably many more good discoveries to make about the microbiomes of buildings.
Dirt is Good
The titular claim comes down to a very weak anecdote, that eating a slurry of dirt from your homeland and water may help with traveler’s diarrhea. Generally, the microbes in dirt wouldn’t survive in your body, so they largely pass through but may have positive (safe for human) interactions with your microbiome first.
It turns out that subways and bathrooms have piles of dead bacteria that fell off human skin, but very little of danger. The older studies that said subways had anthrax in them used a method for trying to sample for known genomes that is unreliable: one author used this technique on tomatos at the store and found evidence of platypus DNA. Also, airplanes, in particular, have relatively sterile air because the air gets pumped through filters six times per minute (amazingly).
Even when bathrooms do literally have poop all over them, touching or eating poop is generally considered a minimal risk by poison control, with possible illness happening within the first 8 hours after contact. The exception to this is the ill shit, which likely carries infections from the ill. This makes shit seem about as scary as saliva, which is surprising!
Is dirt really good? For kids, yes. But for adults, there is little evidence. Does the microbiome help? Mostly it helps us because there are microbes everywhere else and some are less enjoyable to host. But the sterile mice, while they lived in captivity without any microbes, did just fine and were less anxious and more bold than regular mice! Gut bacteria does have some role in endocrine regulation, which is nice to think about. Microbes are powerful, and only sometimes actually good.
This is a bit weird, but swallowing microbes in yogurt can change the balance of your microbiome. It’s like importing animals to island countries, sometimes you get an invasive species and sometimes you get a good contributor and sometimes the new dudes just die. Seems to conflict with the “your microbiome is stable” claim, but the idea is that probiotics can restore stability during periods of weirdness.
Anyway, this book recommends yogurt for everything and really insists that it tastes good. (I don’t like yogurt so found their claim that it tastes good annoying. Are all your claims so personality-driven and cute? Here I worried about Blakeslee’s culpability.) They also point out that honey has many antibiotics in it, but don’t really do the math on whether this helps anyone or is just a fun fact.
Kids and Stuff
Sadly, dirt is mostly just good for kids. Children who suck their thumb (even as teenagers) have stronger immune systems and less allergies because they are eating small amounts of random microbes all the time. Children who grow up with dogs and farm animals get similar results, for similar reasons.
There is a tiny moment of speculation that a civilization with dogs will have an advantage over one without, because it’s been exposed to the dog microbes. But they don’t go far with this and it’s really tantamount to the usual cosmopolitan advantage with germs and imperial adventure.
The vast bulk of the book is an infinite lecture on how you might raise your child if you believed this nascent science has all the answers. I hope the mistake here is obvious: there are a lot of factors in questions of health, diet, behavior, and the rest! The microbiome can add to our understanding, but don’t just ignore all the rest because the science is less fun or sexy!
There are even comments about diets for adults and how to hire good help, assuming you’re rich. I’m including a photo of some of this wasteland here so you can decide I am wrong and this kind of content is worth reading.
Conclusion: Read Other Sources
I’m left with a better understanding of the role of a (top notch) popular science writer: translate this new body of scientific research into a book one rich person can buy for another so they both feel that their decisions are based on objective thought and the greatest their civilization has to offer. I’m sure Blakeslee is capable of more, but I certainly respect how a book like this has a shot at readership and even mass sales if the right marketing events were to happen with it. Realistically, though, I probably would have learned more about microbes by reading wikipedia for an equal period of time. For instance, Wikipedia is much stronger on the Hygiene Hypothesis, microbiota of buildings, and generally more holistic consideration of health topics.
How much of a type of microbe does it take to cause an infection? What are the costs of vaccination or a “strong immune system” in terms of microbiomes and their externalities to the body? What are some known or speculative mechanisms by which microbes contribute to cancer or other major killers? What models of ecosystem and environment can be applied with what value to the behaviors of microbiota? I guess I can thank this book for my enthusiasm for new questions it fails to answer.