The New Yorker:
Ancient peoples knew none of this biology, but they were certain of blood’s importance and fascinated by its mystery. For them, blood was something hidden—visible only when flowing from a wound, or during childbirth, miscarriage, and menstruation—so it became a symbol both of life and of death.
To control blood was to master mortality, so it is unsurprising that blood features prominently in many religious traditions, and that, though our understanding of its functions is more sophisticated than ever, we remain in thrall to its primal mystique.
Along with water, blood is the most important liquid in the world. I still remember the first time I realized its power. I banged my head on the ground playing as a kid and it caused a huge cut that bled profusely. It didn’t really hurt much so I walked home, blood streaming down my face. I got in the house and said, “Mommy, I cut myself.” My mom turned around and saw me and immediately freaked the hell out.