Ninety Percent of Human Being Not Human

Scientists at the National Institutes of Health recently published an analysis of 178 genomes from microbes that live in or on the human body, and have plans to expand their reference collection to nearly a thousand genomes.

Dubbed the human microbiome, this set of fungi, bacteria, and viruses are known to outnumber human cells 10 to 1 and play a critical role in health and disease. According to Human Microbiome Project leader Francis S. Collins, M.D., Ph.D. "We are only at the very beginning of a fascinating voyage that will transform how we diagnose, treat and ultimately, prevent many health conditions."

Published in the May 21 issue of the journal Science, "this initial work lays the foundation for this ambitious project and is critical for understanding the role that the microbiome plays in human health and disease," says Collins.

This initial stage of the HMP focused on gut bacteria and follows on the heels of a 2006 study published by The Institute for Genomic Research documenting microbial genes that code for enzymes that humans need to digest food. This study demonstrated that certain gut bacteria synthesize vitamins which are essential to bodily function, and break down plant sugars which humans could not otherwise digest.

Scientists have also linked imbalances in gut flora to obesity, gastroesophageal reflux, ulcers, and certain cancers. In 2009, University of Michigan scientists published findings in Infection and Immunity demonstrating that certain antibiotics can cause disruptions in the microbiome that can be difficult to reverse. According to lead author Vincent B. Young, M.D., Ph.D., “antibiotic treatments caused significant changes in the gut microbial community. . . we may be doing long-term damage to our close friends.”

The findings extend a quickly growing body of research highlighting the biodiversity of life constituting the totality of a human being. Last year, National Human Genome Research Institute researchers documented that our skin is also home to a much wider array of bacteria than previously thought.

The microbiome is not limited just to bacteria. A recent study published in Nature by University of Texas at Arlington biology professor Cédric Feschotte, suggests that eight percent of what was thought to be human DNA actually comes from viruses.

Perhaps even more surprising is that certain strains called endogenous retroviruses (ERVs) play a critical role in healthy pregnancy. ERVs are similar in function to HIV and are thought to protect a human fetus from being targeted for destruction by the immune system.

It is a Brave New World for biology as new discoveries continue to pummel our foundational beliefs about what it means to be a healthy human being. As these new ideas become integrated into clinical practice we can expect a revolution in medicine that will result in our current methods of treatment one day being viewed as crude as the bloodletting of the 19th century.