Only 1/10th of the cells in a human are human; the rest are microbes. There are 1,000 species in our mouths, another 1,000 in our guts, another 500 on our skins, and those with vaginas have yet another 500 species.
Analysis has shown that a tenth of the chemicals used in our body come to us via our gut microbes. “We are what we feed our bacteria and what they give us.”
(via Long Views, the blog of the Long Now Foundation)