Ecosystems come in all shapes and sizes, often without distinct boundaries. And what happens in one ecosystem affects other ecosystems.
We can even consider the human body as an ecosystem, or perhaps more correctly as a number of interrelated ecosystems. According to a recent article in the scientific journal Nature, "The human body is one of the most important ecological study sites of the coming decade."
The article's author, David A. Relman, chief of infectious diseases at Veterans Affairs Palo Alto Health Care System in California, writes: "Humans depend on the microbial communities that colonize them for a surprising suite of benefits. These include: extracting energy from food, educating the immune system and protection from pathogens. Yet, despite the recent attention to this indigenous microbiota, we are relatively ignorant of what our 'extended self' comprises or how it works."
If we didn't have microbes, which are mainly bacteria, living in and on us, we wouldn't be able to digest our food or breathe properly, and we'd be more vulnerable to numerous types of disease and infection. Scientists estimate that our bodies contain 10 times as many bacteria as human cells, numbering around 100 trillion, and that the human gut alone contains 500 to 1,000 species of bacteria.
The microbes that help our body function properly are referred to as "normal flora" or "microbiota". But, like all ecosystems, our body's ecosystems can be disrupted. If we pollute our bodies, either intentionally or unintentionally, the normal flora can become overwhelmed to the point that they don't function as well as they should. Sometimes this may result simply in a case of upset stomach or indigestion, but often, especially if the pollution is ongoing, it can result in serious disease and death.
What we expose our bodies and the microbes within them to can also have unintended consequences. Although antibiotics have offered a lot of benefits to human health, we're now seeing that decades of their use, often as "growth promoters" in feed for chickens, hogs, and cows, is leading to new illnesses and infections as sometimes-harmful bacteria evolve to be resistant to antibiotics and to our own microbial defences.
The more we learn about the microbial communities in our own bodies, the more we see that a balance must be maintained, for our own sake and for the sake of our human communities. According to New York microbiology professor Martin J. Blaser, "evolution has selected for those microbial populations that maintain and increase the fitness of both individual hosts and the group as a whole."
If we want our own bodies to be healthy, we must ensure that we have access to wholesome food, clean water, and good air. And we should avoid exposing ourselves to anything that would negatively affect the health of our own cells or the microbes that keep those cells healthy.
This is really no different than what happens in all ecosystems. If we put too much garbage and pollution in to the air, water, or ground, we upset the balance created by all the organisms and natural cycles in the environment. Our planet itself has a lot of similarities to the human body. Water circulates around and through the Earth in a complex hydrological cycle, regulating temperature and keeping plants and animals alive, just as blood circulates through our bodies. The natural organisms of the Earth's ecosystems, like the microbes in our bodies, also offer numerous services that we rely on to survive and be healthy.
And for both the human body and the Earth, carbon is an essential element. Carbon is the second most abundant element in the human body, after oxygen, and it also cycles through the Earth, its inhabitants, and its atmosphere. Normally, carbon is absorbed from the atmosphere though photosynthesis and is put back through respiration and decay. But when we upset the balance by cutting down too many of the plants or trees that absorb the carbon and by burning fuels that put too much carbon back into the atmosphere, we put the Earth's health, and thus the health of all of us, at risk.
We must learn to treat the Earth as we would treat ourselves. After all, we are part of nature, and if we don't look after its health, we aren't looking after our own health.