Circumcision has been known for many, many years now to reduce the chance of AIDS...
Two villages....not all that far from each other.
One had all their males circumcised...the other did not. All due to religious beliefs...
The men of the both villages frequented the same places....
More men of the un-circumcised villager's contracted the HIV virus...than the circumcised villager's....
There was direct correlation....
fwiw-