Human sacrifice and stratified societies
There's a study published on Nature.com which gave a hypothesis that human sacrifice legitimizes political and social structures, as a means to stabilize social stratification.
The hypothesis hasn't been subjected to cross cultural tests yet.
From a diverse sample of traditional Austronesian cultures and application of Bayesian phylogenetic methods, it has been found that human sacrifice stabilizes social stratification once the stratification has existed.
The results of the study had shown a dark link between human sacrifice and hierarchical societies.
It would then seem plausible that egalitarian societies may not have indulged in human sacrifice, in contrast to the stratified societies.