According to the Gospels, John the Baptist fulfilled Old Testament prophecy for a messenger to prepare the way for the Messiah. A Gnostic ethno-religion called the Mandaeans, who claim to be direct descendants of Adam, reject this story. For them, Jesus was a false Messiah. John was always the highest prophet.
Fittingly, the Mandaeans’ signature practice is baptism, preferably practiced in a river, every week. In the 1st century, persecution in Jerusalem drove them to modern-day Iraq, where most adherents remained until the 2003 U.S. invasion. Violence dispersed the native community: today, some 80% of Mandaeans are believed to live outside the Middle East, in places like the Sydney suburbs and Worcester, Massachusetts.
There is traditionally no Mandaean conversion, nor intermarriage. Suddenly, after almost two millennia, their chances at long-term survival are so dire.