Religion and seasonality. 7-days as a unit of measurement is written into unamendable documents hold as holy by all Judaist monotheisms (Jewish, Christian and Islamic). The ciclical experience of seasonal-weather and daylight-lenght changes are also too powerful to deny.
AFAIK, Islam traces its roots back to Abraham, who was Judah's great-grandfather. So it would seem more appropriate to call it an Abrahamic religion, no?
