 In 2007, the ATG16L1 gene has been implicated in Crohn's disease, which may induce autophagy and hinder the body's ability to attack invasive bacteria.Another study has theorized that the human immune system traditionally evolved with the presence of parasites inside the body and that the lack thereof due to modern hygiene standards has weakened the immune system.Test subjects were reintroduced to harmless parasites, with positive response.