Newborns get a lot from their mother. They have very little stomach acid, so whatever they are getting goes straight through to their gut.
It's not just food as many commenters are pointing out. It could be from what people are drinking, even water, if oral delivery is not sanitized.
So if the choice is between unsanitary water or sterile and containing chlorine, etc., which has the effect of strengthening the microbiota so that the resulting population increases perceived wellness in the host organism’s sociopolitical fitness, its simple enough, we all stop eating and drinking for ultimate safety and maximum paperclips.
Heh, if so, I wonder if there is a correlation between social anxiety and babies who relied on formula instead of breastfeeding.
The entry point to the gut is from the mouth so because of that, I think food is where most of the gut bacteria comes from.
Sure, as long as you hold your mouth and nose closed when not eating.
You have a back door as well for the gut that tends to open at least once a day. We know fecal matter is in the air in most bathrooms. It wouldn't surprise me if you got an infusion of community fecal biome right into your anus every time you used a restroom that isn't your own.
Yes but usually when the back door opens things are exiting the gut rather then going in. So I don’t think that counts.
There are cases where things do enter the back door but I think that’s just humans getting creative and it wasn’t designed for entry.
Its not like there is positive air flow keeping any microbes in the air out and away. If something lands on there it can probably colonize then spread to the inside slipping through the sphincter.