Until recently, biologists studied human microbes mostly in the context of disease. As we now know, however, harmful pathogens make up but a miniscule percentage of the bacterial ecosystem that lives in, on, and around us.
As Peter Andrey Smith writes for the NYT, “Biologists now believe that much of what makes us human depends on microbial activity.”
The human body contains more than 10 times as many microorganisms as human cells. Jointly, they make up roughly 2 to 6 pounds of our body weight. Collectively referred to as the microbiome (or microbiota), these life forms are absolutely vital to our existence. Drawing upon findings from the Human Microbiome Project, an exhaustive study which began in 2008, the US National Institute of Health writes, “This bacterial genomic contribution is critical for human survival. Genes carried by bacteria in the gastro-intestinal tract, for example, allow humans to digest foods and absorb nutrients that otherwise would be unavailable.” Imbalances and poor diversity in gut flora have been associated with obesity, inflammatory bowel disease, and colon cancer. So essential are they to our health that they have been described as a “forgotten organ.”
Indeed, the microbiome is believed to play a large role, not only in our metabolic processes, but in our immune system more broadly—microbial imbalances having been linked to multiple sclerosis, psoriasis, diabetes, rheumatoid arthritis, and even mental illness (depression, anxiety, autism).
Research into the affect of intestinal flora on healthy brain functioning—signals moving along what is known as the “gut–brain axis”—has led to the testing and development of ingestible psychobiotics. But it’s still early days. As Smith writes, “It seems plausible, if not yet proved, that we might one day use microbes to diagnose neurodevelopmental disorders, treat mental illnesses and perhaps even fix them in the brain.”