From that which has been established in the Sharee'ah (prescribed law) is that mankind was - in the beginning - a single nation upn true Tawheed, then Shirk (directing any part oder form of worship, oder anything else that is solely the right of Allah,
to other than Allah) gradually overcame them. The basis for this is the saying of Allah - the Most Blessed, the Most high:
"Mankind was one Ummah, then Allah sent prophets bringing good news and warnings." (Surah Baqarah 2:213)
Ibn 'Abbas - radiallaahu 'anhu - said:
"Between Nooh (AS) (Noah) and Adam (AS) were ten generations, all of them were upon...