The latest research into the genetics of the human microbiome is taking to a whole new level the old (and not always fruitful) argument about whether nature or nurture is a more important influence in our lives.
In the past few days, Science Express published a paper that demonstrated that friendly (or commensal) bacteria don't just passively crowd out the disease-causing ones. They actively fight back after an infection by taking advantage of selective pressure to force the disease-causing germs to become less fit and eventually die off. (Of course, the bacteria don't "know" what they're doing in any sense of the word. It's just that the ones who are successful at doing it survive.)
Similarly, Nature recently published an article that detailed how the microbial community living inside residents of the U.S. was not as diverse as that inside families living in Malawi or the Venezuelan Amazon. (Whether that difference has any deleterious health effects and why is another story.) (Scientific American is part of Nature Publishing Group.)
The point is that the microbes that live inside, on and around us all ultimately come from the environment. And these commensal bacteria shape our lives every bit as much as our genetic inheritance does. In fact, in many cases, the genes found in these microbes allow us to do something—like digest the fiber in oranges—that our own genes cannot.
The old dichotomy of nature vs. nurture is meaningless when what we think of as our nature—namely the genes that make us who we are—can come from our parents or our microbes.