Strangers Stink More Than Friends

Sheesh, did something die in here? No, but we're more likely to think that strangers rather than friends in close proximity smell badly.
Researchers at St. Andrews University asked students to assess sweaty t-shirts, one of which was labeled with St. Andrews University, another which was labeled with a rival school, and one with no label. The participants tended to rate the shirt from their tribal group--that is, their own university--as less stinky. Tom Jacobs explains in the Pacific Standard:

The key result: Participants whose identity as a St. Andrews student was made salient "went to wash their hands more quickly, and used more soap," after smelling a shirt with either their rival's logo or no logo.
They rushed to the hand sanitizing station after smelling the shirt with the rival school's logo, getting there in three and one-half seconds (on average). In contrast, those who smelled a shirt with their own school's logo ambled over; it took about six seconds. It seems they were significantly less bothered by the stink.
These results make sense from an evolutionary perspective in that members of a prehistoric tribe couldn't collaborate very easily if they found one another revolting. "Groups involve not only a gathering of minds, but also of sweaty, smelly, tactile bodies," the researchers note. "It is impossible to work with people if you cannot stand their physical presence."