As soon as we are born, bacteria move in. They stake claims in our digestive and respiratory tracts, our teeth, our skin. They establish increasingly complex communities, like a forest that gradually takes over a clearing. By the time we’re a few years old, these communities have matured, and we carry them with us, more or less, for our entire lives. Our bodies harbor 100 trillion bacterial cells, outnumbering our human cells 10 to one. It’s easy to ignore this astonishing fact. Bacteria are tiny in comparison to human cells; they contribute just a few pounds to our weight and remain invisible to us.
It’s also been easy for science to overlook their role in our bodies and our health. Researchers have largely concerned themselves with bacteria’s negative role as pathogens: The devastating effects of a handful of infectious organisms have always seemed more urgent than what has been considered a benign and relatively unimportant relationship with “good” bacteria. In the intestine, the bacterial hub of the body that teems with trillions of microbes, they have traditionally been called “commensal” organisms — literally, eating at the same table. The moniker suggests that while we’ve known for decades that gut bacteria help digestion and prevent infections, they are little more than ever-present dinner guests.
But there’s a growing consensus among scientists that the relationship between us and our microbes is much more of a two-way street. With new technologies that allow scientists to better identify and study the organisms that live in and on us, we’ve become aware that bacteria, though tiny, are powerful chemical factories that fundamentally affect how the human body functions. They are not simply random squatters, but organized communities that evolve with us and are passed down from generation to generation. Through research that has blurred the boundary between medical and environmental microbiology, we’re beginning to understand that because the human body constitutes their environment, these microbial communities have been forced to adapt to changes in our diets, health, and lifestyle choices. Yet they, in turn, are also part of our environments, and our bodies have adapted to them. Our dinner guests, it seems, have shaped the very path of human evolution.
In October, researchers in several countries launched the International Human Microbiome Consortium, an effort to characterize the role of microbes in the human body. Just over a year ago, the National Institutes of Health also launched its own Human Microbiome Project. These new efforts represent a formal recognition of bacteria’s far-reaching influence, including their contributions to human health and certain illnesses. “This could be the basis of a whole new way of looking at disease,” said microbiologist Margaret McFall-Ngai at the 108th General Meeting of the American Society for Microbiology in Boston last June. But the emerging science of human-microbe symbiosis has an even greater implication. “Human beings are not really individuals; they’re communities of organisms,” says McFall-Ngai. It’s not just that our bodies serve as a habitat for other organisms; it’s also that we function with them as a collective. As the profound interrelationship between humans and microbes becomes more apparent, the distinction between host and hosted has become both less clear and less important — together we operate as a constantly evolving man-microbe kibbutz. Which raises a startling implication: If being Homo sapiens through and through implied a certain authority over our corporeal selves, we are now forced to relinquish some of that control to our inner-dwelling microbes. Ironically, the human ingenuity that drives us to understand more about ourselves is revealing that we’re much less “human” than we once thought. (continue a ler aqui).