Why did early human societies practice violent human sacrifice?

Human sacrifice seems horrifying and costly. But there might be a reason so many early human societies practiced it.

Human Sacrifice May Have Helped Create Complex Societies

The Anti-vaccine Right Literally Brought Human Sacrifice to America - The Atlantic

The Highest Altar: Human Sacrifice in Ancient Greece - Femmina Classica

BBC - History - Ancient History in depth: The Practice of Human Sacrifice

Ancient Greek Human Sacrifice at Mountaintop Altar? - Biblical Archaeology Society

Top 10 Bizarre Methods of Human Sacrifice - Listverse

Early Europeans Practiced Human Sacrifice

Human Sacrifice & The Aztecs: How & Why Did They Practice This Ritual?

Human sacrifice - Wikipedia

Eating people is wrong – but it's also widespread and sacred

Why Did the Aztecs Practice Human Sacrifice: Uncovering the Ancient Aztec Rituals - Old World Gods

Human sacrifice - Wikipedia

Are humans more violent than ever?

Ancient Cultures That Practiced Human Sacrifice, by The Mystery Writer

Exclusive: Ancient Mass Child Sacrifice in Peru May Be World's Largest