Why our ancestors drilled holes in each other's skulls

For a large part of human prehistory, people around the world practised trepanation: a crude surgical procedure that involves forming a hole in the skull of a living person by either drilling, cutting or scraping away layers of bone with a sharp implement. To date, thousands of skulls bearing signs of trepanation have been unearthed at archaeological sites across the world. But despite its apparent importance, scientists are still not completely agreed on why our ancestors performed trepanation.
Read more: http://www.bbc.com/earth/story/20160826-why-our-ancestors-drilled-holes-in-each-others-skulls?source=Snapzu