I Contain Multitudes

Yong emphasizes frequently that symbiosis is neutral, even though it may seem that the relationship between host and microbe can be net positive. This neutrality comes from the fact that microbes are also living creatures that have their own interests in mind; they, too, need food and shelter and will put those directives above their hosts. Sometimes the need of the host and the microbe align, or the host may make room for the microbe, but the host still must keep the microbes in line.

Chapters 4 and 5 both cover the ways in which microbes impact us negatively. It’s also important to understand the neutrality of symbiosis in the same way that random mutation in evolution is neutral. A mutation can be net positive, negative, or zero, but it will still impact the fitness of the individual. The same goes for the microbes that we host, or the ones that sneak in and cause havoc. We would not have evolved without bacteria, but that doesn’t mean their presence was always a good thing.

This text is filled with examples of how microbes have interacted with animals in various contexts, and they vary in their levels of helpfulness. As we learn how to manipulate our microbiome, the outcome of that manipulation will be just as neutral as the initial relationship. It’s hard to gauge whether a change we cause to our biome will benefit our microbes and how that will impact both parties in the long run.

As science begins to tease apart the way our microbiome impacts our health, it becomes important to be critical in the studies that come out on those impacts. As Yong mentions, particularly in Chapter 5, one type of bacteria is most likely not the cause of a disease. We must consider the entire microbiome, the ecosystem, our immune system, and the other organ systems in our body. Bacteria are likely one part of the equation, but eliminating or adding a single type of bacteria likely won’t cure the disease.

Even in the case of C. diff, while that one type of bacteria has been narrowed down as the cause of illness, the solution is the replacement of an entire ecosystem. The disruption of the microbial ecosystem allowed C. diff  to move in.

Finding connections between bacteria and health gives us information on the role our microbes play in health conditions, but one study that suggests microbes cause obesity in mice is not definitive; studies on animals do not translate over into humans, and until clinical trials are conducted, we can’t know for sure what connection our microbes play in our health. Some people oversell the role our microbes play, and that can be dangerous, as these studies can generate headlines that misinform the public. Both citizens and scientists must maintain a critical eye as we watch this new field of study unfold.