Intro to human microbiome Humans (and all other animals) have evolved to depend on their microbiome, which helps develop and maintain our immune, mental, cognitive, and physical health. The microbiome consists mostly of bacteria, but also includes viruses, bacteriophages, fungi (yeasts, molds...), and parasites. There are ~40 trillion microbial cells in a human body (equal to the number of our cells), represented by ~1150 species in the gut and ~450 species in saliva. Vaginal, skin, and other microbiomes have far fewer species and cells, but they also play an important role in our health. The vast majority of the species in the human microbiome support our health. One of the main reasons for the chronic disease epidemic in the developed countries is that we have been systematically destroying our microbiome (antibiotics, food preservatives, sterile life, sterile food, no playing in nature...). Being "dirty" used to be the norm for 1000s of years, but has become bad in the las...