To start with your second question, there are some indications that stone age humans were carrying out human sacrifice, though not entirely conclusive.
In contrast, a lot of evidence of human sacrifice has been found for the neolithic era, at the beginning phase of human settling. This predates larger settlements but is generally found for human groups that had abaondoned their hunter-gathering in favor of agriculture.
What changed when settlements turned into larger, organized societies is that human sacrifice became a way to legitimize (religious) authority and class systems. The study in the link provides an analysis of the connection between the rise of organized religions and human sacrifice in particular.