Animal sacrifice is much older; human sacrifice was used when the situation seemed to suggest that an animal sacrifice wouldn’t get it done. Blegen’s discovery of a Linear B archive on the first morning he dug at Pylos happily followed Ventris’ discovery that the text concealed Greek, a possibility brushed off by Linear B’s discoverer, Arthur Evans. On what was apparently the last tablet in the Pylos archive was a scrawl of Linear B recording that two human sacrifices were being made, one man and one woman. The last information on the tablet was that troops were being sent. From the same period there is the Iliad’s account of human sacrifice.
Of course, cannibalism has been practiced for a really long time, though it’s a judgment call whether that was ever considered a religious rite.
Whoops. Meant to refer to Arthur Evans as “the late”. ;’) Evans had the first batch of Knossos tablets laid out on the hillside; there was a rain in the night, and the tablets were destroyed. Oops.