Missionaries and cannibals

This is a classic.

Adlai Waksman: (Mis)quoted from memory from "Thought Starters" by Ted Cook:

A cannibal chieftain asked the visiting missionary, "How do your people eat up the thousands who are killed in your wars?" The missionary recoiled in horror, "We don't eat human flesh!" So the cannibal blandly asked, "So what do you kill them for?"

Three missionaries are travelling in a jungle accompanied by an equal number of cannibals. The company arrives at a river. There is a boat which is needed for crossing the river.

Unfortunately, the boat can only hold two people at a time. Neither shore of the river may have more cannibals than missionaries, because if this happens, the poor evangelists get to the menu of the aboriginees.

How do all six get across the river, and how many boat trips does it take? No swimming, no towing the boat with a rope, or anything of the sort. A cannibal in the boat is counted as a cannibal on the shore for the purposes of attacking missionaires.

Think it over!

Then check the answer here.

Published in Njet Problem! collection 1996-09-06.