Way I figure it the enemy wants to eliminate all those who still retain a bit of Adam and Noah's original human DNA. But since Noah was the last his wife therefore & their sons were not purely Adam's DNA read the Book of Enoch they were interbreeding us with animals. All animals have positive blood only a small percentage of the world's population has negative blood and the rarest of all blood types is AB- so I think we can assume that was likely Adam, Eve, Noah and Jesus' blood type. This leads me to believe that all those not of the O type blood may be those to whom they hope to track. A person has A or B blood type that means they have an O and A or B otherwise they would be AB. For instance an AB parent with an O parent splits the A and the B giving the option of producing an A, B, or O blood type but not another AB which accounts for the rarity of the AB blood type. Any time a negative Mom conceives a second child by a positive dad the baby was rejected in the womb.