"As I saw it, the relationship between a typical African and his dog is one of tangible mutualism. I say tangible because the African sees himself as the dominant creature not to be bothered by the dog, but nevertheless responsible for providing for it."
Why is a comma necessary before but? If you have a comma before a coordinating conjunction, doesn't that mean both sides of the "but" have to be independent clauses? However, in this case, "nevertheless responsible for providing for it" doesn't make sense by itself so it is not an independent clause. If it is wrong to put a semi colon in the place of that comma, surely it should be wrong to put a comma there as well.