First of all, I'm a complete layman in Biology. Recently I read "The evidence for evolution" by Richard Dawkins. Pondering about this matter, I wondered about the origin of human gut bacteria (could be more generalized to mammal gut bacteria).
Generally, I see two possibilities:
These bacteria are
- acquired later on through the environment (probably after birth) or
- they are produced by the organism itself
The former option seems to me a little bit too vulnerable to be true (different food, different bacteria due to geographical location, etc.)
The latter option seems baffling to me. Bacteria are, as far as I know, independent lifeforms. Is it possible, that our DNA contains the information for other lifeforms as well?