The missionary and the black sheep

A young missionary travels to Senegal to teach God's way to a local tribe.

Upon reaching the village, he is not well received by the inhabitants, but he slowly and steadily create contact.
After many years he's finally accepted by the people and goes along well with everyone, until one day the chief's daughter gives birth to a white child.

Infuriated but not ungrateful for what the missionary has done for the village, he gives him one chance to explain himself in private.

The young man, who is innocent, tells him "I have nothing to do with it, it is just a hazard of the genetics. It's the same as with sheeps, most of them are white but sometimes a black one is born for no reason".

The chief steps back a little, gives a frightened look to the missionary, then whispers : "Ok, I won't say a word about my daugther, but don't you tell anyone about the sheep"