RICH MELTING POT. “Gene transfer is common in the gut. A broad assessment of lateral gene transfer events between bacteria from a multitude of environments showed that human-associated bacteria are 25 times more likely to exchange genetic material than bacteria from other environments, and that closely related human-associated bacteria exhibit horizontal gene transfer (HGT) in 20% to 40% of all pairwise bacterial comparisons.”
http://www.jci.org/articles/view/72333