Board Thread:Spoilers/@comment-28118206-20160403030006/@comment-97.105.33.202-20170911194440

When Becca came back to earth she brought the night blood with her. The first people that came out from the tower of what was soon to be "Polis" were the first nightbloods. Titus even mentioned it to Murphy when he tried to explain how Becca fell from the Sky like they did. Not sure if Becca had kids but the most probable thing is that she injected the night blood into those people in Haz Mat suites and as they reproduced then the nightblood became hereditary. Also, I guess the point was for everyone to eventually become nightbloods but somehow these Maya acting people keep getting them killed in conclaves untill one remains to be the commander.