circumcision thing is a strong type of proof. I red in a number of places that the 8th day after birth is not just "normal level" but the HIGHEST of the male's ENTIRE life
I've never heard of this before and cannot find any evidence for this (which don't mean much).
If it is true couldn't it have been thru experience? You can imagine a very experienced circumciser who notices that babies tend to heal better and don't bleed as much if you circumcise on the 8th day and it finds it way into the lore. Nothing inspired there.
Wouldn't most ancient medical treatment have been found thru trial and error? To a degree I suppose it is still the same today.