In antiquity, the woman’s periodic hemorrhage and her further loss of blood at childbirth early suggested blood as the creator of the child.  Some ancients believed soul resided in blood.  Next, any place where blood was shed became the property of the injured person or group. 
Human secretions, being definitely magical, were highly regarded; blood and urine were thus among the earliest medicines and were soon augmented by roots and various salts.  The practice of paying “blood money” also came into vogue as a substitute for blood vengeance. Moses was the first in abolish this practices. 
The Phrygian ceremonies were imposing but degrading; their bloody festivals indicate how degraded and primitive these Levantine mysteries became. The most holy day was Black Friday, the “day of blood,” commemorating the self-inflicted death of Attis.  Kings and royal blood have long been regarded as supernatural, and some Urantia peoples still regard their rulers as having had a divine origin. 
The barbarous idea of penance by shedding blood represents a religion wholly puerile and primitive.  The Hebrews believed that “without the shedding of blood there could be no remission of sin.  Philo of Alexandria taught deliverance from the doctrine of forgiveness only by the shedding of blood. 
The temple pavement stained with the blood of the sacrificial animals, the gory hands of the priests, the moaning of the dying animals, all of that made Jesus sick when he first saw it.  Many still depend upon blood for salvation, but it has at least become figurative, symbolic, and mystic. 
One of the most serviceable and complex episodes in the evolution of the higher types of animals consisted in the development of the ability of the iron in the circulating blood cells to perform in the double role of oxygen carrier and carbon dioxide remover. But other metals can be made to serve the same purpose. The cuttlefish employs copper for this function, and the sea squirt utilizes vanadium.  Blood retains salinity of ancestors’ ocean environment in which life began.