Many (if not most or even all) ancient religions and cultures had some form of human sacrifice, though it seems that few of them engaged in the practice very often. As researchers have looked more closely, they seem to be finding more and more examples of sacrifice in ancient religions. In fact, they are finding examples of human sacrifice that don't appear to fit with the categories they have been using.
So it looks like we still have quite a bit to learn about the sacrifice of humans, but it's unclear whether the archaeological evidence will provide us with that information. The more we learn about human sacrifice, though, the more we'll probably learn about the earliest development of both religion and civilization.
Researchers are finding that although human sacrifice was not frequent in most cultures, it was pervasive, taking place at one time or another in just about every ancient civilization in which someone had the rank and power to decide who died, Verano says. Although human sacrifice was seen as barbaric by classical times, it persisted in Rome, the Americas, and elsewhere until the rise of Judeo-Christian and Islamic religions that condemned it. Across cultures, most cases shared twin motivations: to please the gods, and to vividly assert and display rulers' power.
For early states, whose rulers were consolidating power, ritual sacrifice seems to have been one way to discourage outside attacks and internal revolt by sowing fear. The cross-cultural data are beginning to give researchers an idea of "key patterns in the origins, motivation, and methods of [sacrifice]," says bioarchaeologist Haagen Klaus of Utah Valley University in Orem. ....
The difference between these deaths and other state-sanctioned killings is that sacrifice is ritualistic. Researchers add that they aren't targeting any particular society; indeed, a major finding is that human sacrifice was found in most emerging city-states around the world, particularly under a new ruler or in times of crisis. At the same time, it was relatively rare within populations. "Not everyone gets a sacrifice at their funeral," Scherer says. Klaus agrees: "There's not a lot of trauma in the populations at large. But a special subset of people did die extremely brutal and violent deaths at a variety of sites." ....
Child "sacrifice doesn't mean giving up those you don't like," Klaus says. "It's giving up those that matter the most." And the Inca may not have thought of their children as dying. "In this very sacred mountain environment, they'd be seen as living with the gods," Reinhard says. "They would, in essence, become deified." ....
As more cases of sacrifice emerge, some defy classification. This suggests that researchers have just begun to exhume the myriad ways that humans killed each other in the name of the gods and the state. "Our ability to see sacrifice in the past was somewhat limited. Now we're able to expand that view," Monge says. "I'd say we're just coming to realize in some measure the enormity of the violence of humans against humans."
Source: Science, May 18, 2012
Although it generally disappeared over time, the principle has survived even down through today. Christianity, for example, is based on the belief in a human (who as also a deity) being sacrificed for humanity's sins. The act is celebrated, not mourned or regretted because key to all of the different forms of human sacrifice is that they are, clearly, a sacrifice: a ritualistic giving up of something valued or valuable in order to achieve some larger goal, like appeasing gods which demand blood in exchange for protection or favor.