A rule has now been found that says that Humans are Living, see the other answers for discussion of that.
This answer specifically addresses the contention that the following rule says that humans are living:
Any living creature has at least 1 point of Constitution. A creature with no Constitution has no body or no metabolism. It is immune to any effect that requires a Fortitude save unless the effect works on objects or is harmless. The creature is also immune to ability damage, ability drain, and energy drain, and automatically fails Constitution checks. A creature with no Constitution cannot tire and thus can run indefinitely without tiring (unless the creature’s description says it cannot run).
While at first glance this rule does seem to cover it there is a rather large hole in the logic. The rule says that all living creatures have a point of constitution.
That means that if humans had no constitution score we would know they are not living. However humans do have a constitution score. Does that mean we know they are living?
Unfortunate it does not.
To give an example lets say you had your friends blindfold you and then everyone puts their mobile phones on the table. A friend tells you "All the iPhones are black". He hands you a phone and says "this phone is black". Can you tell if it is an iPhone?
You can't. If he told you it was an iPhone you would be able to tell him the colour, but from the colour on its own you have no idea because there is also a black Samsung, and a black Sony in amongst the other colours and brands of phone on the table.
This is the exact same situation. The lack of a con score means something is not living but by a strict reading of the rules the presence of a con score does not mean the opposite.
Clearly humans are intended to be living, and in fact the intention seems to be that anything without constitution is not living while anything with a constitution score is living. However that is not what this particular Rule As Written says.