Summary of I Contain Multitudes by Ed Yong

BookSummaryClub Blog Summary of I Contain Multitudes by Ed Yong

When most people think about bacteria and microbes they’re not the most positive thoughts. They are those tiny, pesky things that make everyone sick and turn us into germophobes. But what about those microbes that are a part of us? There are more microbes in the human body than cells. They’re not the bad guys. In fact, our bodies would not be able to function correctly without them.

So, maybe we should learn to understand just how intertwined the lives of humans and microbes really are. They have been a part of our evolution and have greatly contributed to the well-being of not only humans but other organisms as well.

In this book summary readers will discover:

  • The story of microbes
  • Humans and animals need microbes
  • Symbiosis and Alliances with microbes
  • The power of the microbiome

Key lesson one: The story of microbes

Microbes have been around much longer than humans. In fact, if we had to scale down the Earth’s existence into a single year, microbes would have come up around March whilst humans would have been born in the last 30 minutes of the last day in December! This means that microbes had established themselves on Earth quite well before humans showed up. In fact, they were around so much longer than us that they actually shaped the planet into what we know today.

Microbes refer to a variety of single-celled organisms including bacteria and fungi. They are so small that it is possible to find approximately one million of these organisms on a pinhead! It’s hard to imagine how something so small could have such a great impact on our lives but microbes are constantly at work. They break down molecules in the air, soil and water playing an important role in nutrient and carbon cycles in our environment. Microbes were also involved in the creation of the Earth’s atmosphere. Before plants came about, microbes were the first ones to use photosynthesis to survive. They used sunlight to convert carbon dioxide and water into sugar which they then consumed. During this process, oxygen was released and the atmosphere was formed.

Microbes have been able to concur every environment on the planet. Whether it be ice-cold conditions in Antarctica or fiery hot volcanoes, microbes have adapted to live in these extreme conditions. Their ability to multiply rapidly means that they can also evolve at rapid rates which are integral to these adaptations. Microbes form a physical link to nearby cells which enables them to pass DNA along to be added to the genome. Therefore, adaptations can spread quickly making the whole process much faster than natural selection.

Key lesson two: Humans and animals need microbes

The human genome contains about 20 000 genes. If microbial genes had to be added to this, the human genome would be approximately 500 times bigger! The unique microbial community we carry is called a microbiome. Microbiomes are unique to each individual, no matter the species. Each body part has a different community of microbes although their functions are the same. It’s almost as if our body has its own ecosystem. 

Each community of microbes has its designated function which ensures that processes run smoothly in the body. So, in a way, microbes enable the health and development of all humans and animals. This means we depend on them. Humans depend on bacteria from the moment they are born. They strengthen our immune system right from the start. Breast milk is rich in nutrients including something called human milk oligosaccharides or HMOs. Babies cannot digest HMOs but the microbes in their gut can. These microbes digest the HMOs and release proteins that babies can digest. An anti-inflammatory protein is also release which coats the baby’s gut and begins to calibrate their developing immune system. 

Another example of the importance of microbes comes from mice. In the guts of mice, a microbe called Bacteroides thetaiotaomicron activates specific genes during development. These genes ensure that the correct blood vessels are formed and that the gut contains the right community of microbes to break down toxins and obtain nutrients.  

Key lesson three: Symbiosis and Alliances with microbes

Microbes have an important part in all life on earth but sometimes these relationships are a bit more special. Take for example the tentiform leafminer. It forms a cocoon on a leaf in order to mature. Its survival is therefore dependent on the leaf remaining on the tree and not falling down. The leafminer has a microbe that produces hormones that ensures that the leaf remains green and does not fall off prematurely. This is why during autumn in the Northern Hemisphere some leaves remain green even when the others have turned yellow, red and orange. 

This is not limited to land. Even little cephalopods in the ocean have also formed a relationship with microbes to aid in their survival. The bobtail squid has a community of microbes that makes its outer layer more hospitable to a specific microbe. When these microbes arrive on the squids surface, they are supplied with nutrients that keep them closely bonded to the squid. These microbes then begin working as the squid’s defence mechanism. They give off a glow that confuses predators from below by mimicking the glow of the moon. 

In addition, since microbes can adapt to just about any living conditions, they can also help other organisms survive. They help animals digest foods that would normally be indigestible for them on their own, provide vitamins to insects so that they can build proteins and are a nutrient-rich source of food for some offspring. A termite’s weight, for example, is 50 per cent microbes which help it digest cellulose. 

As much as these relationships occur naturally, sometimes alliances are formed with microbes because of the reactions that will occur. You see, microbes in their natural habitats are harmless, they carry on doing what they are supposed to. Once they are taken out of this natural habitat and placed somewhere else, there could be repercussions. The bacteria in our gut for example is completely harmless as it helps us digest food. However, if these bacteria were to get onto our skin somehow, they could infect any wounds we may have and cause a whole slew of problems. 

This knowledge is used by farmers who use Bacillus thuringiensis as a pesticide. When this microbe comes into contact with a caterpillar, it makes holes in the insect’s stomach. This causes bacteria to leak into its bloodstream leading to the insect’s death. Insects try to prevent this by keeping their microbes in cells called bacteriocytes. The bacteriocytes provide the microbes with nutrients whilst also protecting them from attack from their own immune system. 

In humans, however, it is a bit more complex given the number of different organs and microbes present in our bodies. There are still some mechanisms though, that ensures that the right microbes stay in the right place. Our gut has a lot of acid present which only allows bacteria that can survive this acidic environment. Mucus, present in most vertebrates, contains bacteriophages that feed on harmful microbes. The biggest mechanism though is our immune system. It produces white blood cells that eliminate any microbes which are in places they are not meant to be. 

Key lesson four: The power of the microbiome

In order for our bodies to function well and maintain a healthy microbiome, certain conditions must be met. Our immune system must be working like a well-oiled machine. Thus, it must be properly calibrated. If our immune system only works on large threats and ignores the smaller ones, there is a possibility that it might neglect a potentially infectious disease. In contrast, if our immune systems attack everything they come into contact with, there is a risk of developing allergic disease. Being exposed to microbes can help to calibrate our immune systems to the optimal setting. Our modern lifestyles, however, actually prevent this from happening. 

The optimal time for this exposure to occur is when we are young. As children, if we are exposed to microbes, our immune system has enough time to calibrate and prevent infectious diseases later on in life. Children are naturally exposed to dirt, dust and mud. Or at least, they used to be. Nowadays, growing up in an urban environment means that children do not get exposed to these things. When you live in a city, your water is sanitized, you have less contact with animals and even foods tend to be overly processed. As much as health trends encourage getting out more, not everyone does and their immune systems pay the price.

There needs to be some competition happening in your microbiome otherwise it will never be ready for a fight when it is needed. It will be so easy fr a bad microbe to set up residence if there is space for it. We, therefore, have to work at building our microbiome and thus immunity. Maintaining a healthy and diverse diet can help the microbes in our gut. There are also prebiotics and probiotics which are found in multiple formulations. The results from probiotics vary as the microbes introduced are not natural to your gut so they don’t really make a lasting impact. Some work is being done on introducing full microbiomes into individuals. This could make treatments more targeted and effective but research still has to be conducted in order to manipulate microbes for specific purposes. 

The key takeaway from I Contain Multitudes is:

Microbes often have a bad reputation but we should not forget the role they have and have had in our lives. They have been around a lot longer than humans have and have literally made the planet what it is today. They are crucial to the carbon and nutrient cycles and have evolved to live in some of the most extreme environments on Earth. The most important thing we should remember however, is that without microbes, our bodies would not function as efficiently as they do. They are vital to our health in so many ways that we should really start paying more attention to them.

How can I implement the lessons learned in I contain Multitudes:

Ensure that you maintain a healthy and diverse diet that includes a lot of fruit and vegetables. This will help maintain a healthy microbiome by introducing and enabling the helpful bacteria in your gut. Also, allow your kids to play outside more in order to build their immunity. Our modern lifestyles inhibit this so we should compensate by making a little more effort to get them to play in the dirt! It really does help.

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