Why do people who live on islands tend to develop very different customs from those who live in other parts of the world

1) They're isolated from the other cultures so they don't have cultural contact with theim

2) their situation is special in that they have a lot of access to the sea (sea food) but with not as mush arable land available (they are restricted to the size of the island) - this influences their customs (less harvest related, more fishing related)