Where does it come from?
Colonization of the human gut starts when the baby is born, specifically, when infants pass through the birth canal. This results in infants being exposed to complex community of microbes and initiates the establishment of intestinal microbiota. At the first year of age, this community of microbes is very simple and widely varies between different individuals. However, after the first year, this microbiota starts to evolve and stabilize and becomes more similar to that of young adults. The final composition of this microbiota in adulthood is thought to be as a result of the initial colonization process at birth.