It has been shown that specific genes in plants promote the incorporation of bacteria into the plant to promote a healthy symbiosis. In this case the bacteria helps the plant by converting nitrogen into a form useful to the plant. (Getting the useful form/s of nitrogen to plants is the main purpose of fertilizer.)
BYU researchers uncover mechanism plants use to promote symbiosis with bacteria
Based on this hard evidence, it is easy to suppose that our own genes may guide the bacterial symbiosis occuring on our sking and in our digestive tract.
